Alternative polyadenylation profiles of susceptible and resistant rice (Oryza sativa L.) in response to bacterial leaf blight using RNA-seq.

BACKGROUND: Alternative polyadenylation (APA) is an important pattern of post-transcriptional regulation of genes widely existing in eukaryotes, involving plant physiological and pathological processes. However, there is a dearth of studies investigating the role of APA profile in rice leaf blight. RESULTS: In this study, we compared the APA profile of leaf blight-susceptible varieties (CT 9737-613P-M) and resistant varieties (NSIC RC154) following bacterial blight infection. Through gene enrichment analysis, we found that the genes of two varieties typically exhibited distal poly(A) (PA) sites that play different roles in two kinds of rice, indicating differential APA regulatory mechanisms. In this process, many disease-resistance genes displayed multiple transcripts via APA. Moreover, we also found five polyadenylation factors of similar expression patterns of rice, highlighting the critical roles of these five factors in rice response to leaf blight about PA locus diversity. CONCLUSION: Notably, the present study provides the first dynamic changes of APA in rice in early response to biotic stresses and proposes a possible functional conjecture of APA in plant immune response, which lays the theoretical foundation for in-depth determination of the role of APA events in plant stress response and other life processes.

Photosynthetic Costs and Impact on Epidemiological Parameters Associated with Ht Resistance Genes in Maize Lines Infected with Exserohilum turcicum.

Northern corn leaf blight, caused by Exserohilum turcicum, is mainly controlled by the use of resistant cultivars. Maize lines carrying individual resistance genes B37Ht1, B37Ht2, B37Ht3, and B37Htn1 express different defense symptoms having an impact on the photosynthetic activity, the accumulation of reactive oxygen species, and epidemiological parameters. Plants were inoculated with a race 0 isolate of E. turcicum conferring a compatible interaction with B37 and incompatible interactions with plants carrying resistance genes. Five days postinoculation (dpi), the resistant lines displayed a reduction in leaf CO2 assimilation of 30 to 80% compared with healthy plants. At 14 dpi, inoculated plants of B37Ht1 showed a significant decrease in leaf CO2 assimilation, similar to B37 (up to 94%). The instantaneous carboxylation efficiency was significantly reduced on inoculated plants of the lines B37Ht2, B37Ht3, and B37Htn1 (54 to 81%) at 5 dpi. Curiously, the reduction in carboxylation efficiency for B37 and B37Ht1 (up to 95%) was higher at 14 dpi than at 5 dpi (up to 81%). At 6 dpi, low levels of H2O2 were detected in B37Ht1, in contrast to B37Htn1, where a high H2O2 level and peroxidase activity were observed. The sporulation rate on B37Ht1, B37Ht3, and B37Htn1 decreased by 92% compared with the susceptible control, whereas strong sporulation occurred in lesions on line B37Ht2. The resistance in maize to E. turcicum conferred by Ht resistance genes is associated with photosynthetic costs and may have quite contrasting effects on host physiology and major epidemiological parameters, such as sporulation, which contributes inoculum for secondary infections.

Identification of candidate gene associated with maize northern leaf blight resistance in a multi-parent population.

KEY MESSAGE: QTL mapping combined with genome-wide association studies, revealed a potential candidate gene for  resistance to northern leaf blight in the tropical CATETO-related maize line YML226, providing a basis for marker-assisted selection of maize varieties Northern leaf blight (NLB) is a foliar disease that can cause severe yield losses in maize. Identifying and utilizing NLB-resistant genes is the most effective way to prevent and control this disease. In this study, five important inbred lines of maize were used as parental lines to construct a multi-parent population for the identification of NLB-resistant loci. QTL mapping and GWAS analysis revealed that QTL qtl_YML226_1, which had the largest phenotypic variance explanation (PVE) of 9.28%, and SNP 5-49,193,921 were co-located in the CATETO-related line YML226. This locus was associated with the candidate gene Zm00001d014471, which encodes a pentatricopeptide repeat (PPR) protein. In the coding region of Zm00001d014471, YML226 had more specific SNPs than the other parental lines. qRT-PCR showed that the relative expressions of Zm00001d014471 in inoculated and uninoculated leaves of YML226 were significantly higher, indicating that the expression of the candidate gene was correlated with NLB resistance. The analysis showed that the higher expression level in YML226 might be caused by SNP mutations. This study identified NLB resistance candidate loci and genes in the tropical maize inbred line YML226 derived from the CATETO germplasm, thereby providing a theoretical basis for using modern marker-assisted breeding techniques to select genetic resources resistant to NLB.

First report of leaf blight disease caused by Aspergillus welwitschiae on Persicaria lapathifolia var. salicifolia in China.

Persicaria lapathifolia var. salicifolia (Sibth.) Miyabe, has long been extensively utilized in traditional medicine for its significant medical values (Seimandi et al, 2021). Despite its extensive use, the leaf blight disease of this plant has never been documented in China. However, in September 2023, the symptoms of leaf blight disease were observed on P. lapathifolia var. salicifolia on the campus of Zhejiang Normal University (29°8'3″ N, 119°37'47″ E), Zhejiang province, China. The disease incidence was 40% on the 50 plants surveyed, according to the field survey. The progression of leaf pathogenesis is mainly divided into three stages. Early symptoms manifested as the light yellow spots on the edges or tips of the leaves, which subsequently developed into brown or yellow irregular lesions and eventually led to the curling and wilting leaves. Thus, the leaf tissues (5 × 5 mm) from the border of diseased and healthy areas were surface-sterilized in 1% sodium hypochlorite for 3 min, followed by 75% ethanol for 30 s, and rinsed three times with sterile water. After drying on sterile filter paper, the leaf tissues were put on PDA medium and cultured at 25°C for 3 days. Seven purified fungal isolates were obtained, and one representative strain was selected for further identification. After that, the isolate was identified by the combination of morphological studies and molecular analysis. The fungi exhibited rapid growth on PDA, attaining a diameter of 80 to 85 mm in 5 days. The colonies were black with a yellow margin, and the reverse sides were light yellow and partly colorless. Moreover, the conidia were brown to black, smooth to slightly rough, measuring 3.2 to 3.8 µm (n = 30) in diameter, with radiated conidial heads and expanded ampulliform phialides under the optical microscope. Therefore, the isolate's characteristics were consistent with the descriptions of Aspergillus welwitschiae (Bres.) Henn. (Gherbawy et al, 2021). To further identify the isolate, the internal transcribed spacer (ITS) region (Gardeset al, 1993) and the second largest RNA polymerase subunit (RPB2) (Liu et al, 1999) were employed for phylogenetic analysis. The obtained sequences were despot in GenBank (Acc. Nos. OR797058 for ITS, OR797058 for RPB2, respectively), and exhibited a high degree of sequence homology to A. welwitschiae (MK450815, MK450818, LC179911, and LC000572), with 99% to 100% identity. Besides, multilocus phylogenetic analysis showed that the isolate gathered into one clade with A. welwitschiae. Based on the integrated morphological and molecular results, the isolate was determined to be A. welwitschiae. Six healthy 1-year-old P. lapathifolia var. salicifolia were used to verify Koch's postulates. Three leaves were wounded with sterile pins and inoculated with the conidial suspension (107 conidia/mL) of isolates, while plants inoculated with sterile water were used as controls. After sealing with plastic wrap for 24 hours, the plants were cultivated at 25 °C and 85% relative humidity. Necrotic lesions were observed on leaves 10 days after inoculation, while the control leaves remained asymptomatic. The fungi were re-isolated from the diseased leaves and identified as the original ones through morphological and molecular identification, confirming Koch's postulates. While A. welwitschiae has been reported to cause the rot disease of Sisal Bole in Brazil (Duarte et al, 2018) and maize ear in Serbia (Nikolic et al., 2023), to our knowledge, this study marks the first report of A. welwitschiae causing leaf blight on P. lapathifolia var. salicifolia in China, extending the host range to A. welwitschiae.

First Report of Aspergillus westerdijkiae Causing Leaf Blight on Rehmannia glutinosa in China.

Rehmannia glutinosa (also known as Chinese foxglove) is a perennial dicotyledonous herb, which plays an important role in traditional Chinese medicine. Its active ingredients have a wide range of pharmacological effects on the blood system, endocrine system, immune system, cardiovascular system, and nervous system (Zhang et al. 2008). In May 2022, leaf blight was observed on 45-day-old R. glutinosa in a seedling nursery in Jiaozuo City (35°01'44.20″N, 113°05'30.63″E), Henan Province, China with an approximate disease incidence up to 54% (~1,300 plants). Irregular brown lesion initially appeared on the tips of basal leaves, then progressed to the entire leaf causing leaf drying out (Supple. Fig. 1-A, B, C). The same symptoms appeared successively in the leaves from the base to the top of the plant, which eventually caused the whole plant to die. To identify the pathogen, eight symptomatic leaves were randomly collected from eight individual plants, and cut into small pieces (5 × 5 mm) at the border of lesions. The pieces were surface disinfected in 75% ethanol for 15 s, followed by 1% NaClO for 1 min, rinsed in sterile water three times, and placed on potato dextrose agar (PDA) medium in the dark for 3 days at 25℃. Finally, 12 purified isolates (DHY1-DHY12) were obtained by using single spore method. Leaves of R. glutinosa seedlings were inoculated with conidial suspension (106 conidia/ml), three plants were inoculated per isolate. Controls were treated with sterilized water. All inoculated and control plants were incubated in a greenhouse at 25℃ under 80 ± 10% humidity and a 8-h/16-h dark/light cycle. This experiment was repeated three times. After 5 days, similar symptoms to those of diseased leaves in the seedling nursery appeared on leaves inoculated with DHY4-DHY10, while plants inoculated with DHY1-DHY3, DHY11-DHY12, and the controls remained asymptomatic (Supple. Fig.1-D, E). The same fungi were re-isolated from diseased leaves, fulfilling Koch's postulates. The causal agents DHY4 to DHY10, showed similar morphology, which were morphologically identified as Aspergillus sp. (Visagie et al. 2014). Isolate DHY5 was selected for further study. On PDA plates, the colonies were covered with white velutinous mycelia (Supple. Fig.1-F). Conidia were ochre yellow and outwards concentric circles. Vesicles were globose, and about 20.1-26.6 µm in diameter (Supple. Fig.1-G). Conidiophore stipes were smooth walled and hyaline, with conidial heads radiating. The conidia were light yellow to orange, exudate clear to orange droplets. The conidia were (2.53-3.25) µm × (2.58-3.47) µm in diameter (n=50) (Supple. Fig.1-H). For further molecular identification, the ITS and TUB gene sequences were amplified with primer pairs ITS1/ITS4 and BT2a/BT2b (Glass and Donaldson. 1995), respectively. BLASTn searches of the ITS (PP355445) and TUB (PP382788) sequences showed 100% and 98.42% similarity to those of A. westerdijkiae (OP237108 and OP700424), respectively. Phylogenetic analysis based on the concatenated sequences of ITS and TUB confirmed that the fungus was A. westerdijkiae, (Supple. Fig.2). A. westerdijkiae was mainly reported on its secondary metabolite ochratoxin A contamination of agricultural products, fruits, and various food products, such as coffee beans (Alvindia et al 2016), grapes (Díaz et al. 2009), oranges and fruit juice (Marino et al. 2009), etc. To our knowledge, this is the first report of A. westerdijkiae causing leaf blight on R. glutinosa in China.

First Report of Leaf Blight Caused by Botryosphaeria dothidea on Aucuba japonica in Zhejiang Province, China.

Aucuba japonica var. variegata Dombrain is a common evergreen cultivated ornamental in China (Li et al. 2016). In December 2022, severe leaf blight on A. japonica was observed next to the Meishiyuan of Zhejiang Normal University (29°8'4″N, 119°37'54″E) in Jinhua City, Zhejiang Province, China. There were seven plants in the surveyed area, and over 50% of leaves were affected. The early symptoms were small gray spot parts with brown borders on the tip of the leaves. Then the grey parts gradually expanded and became brownish black. In severe cases, the whole leaves became black and blighted. To identify the pathogen, 5 symptomatic leaves were randomly collected from 5 plants and cut into small pieces (5 mm × 5 mm), surface disinfected in 1% sodium hypochlorite solution for 3 min, followed by 75% alcohol for 30 s, then rinsed in sterile distilled water thrice. Tissues were cultured on potato dextrose agar (PDA) and incubated at 28°C for 7 days. Pure cultures were obtained by the single-spore method. Thirteen strains were isolates from the tissues, and nine of them showed similar morphological characteristics. Colonies were white initially, then became gray. The undersides of the colonies became black gradually. Hyaline, fusiform conidia (n = 30) were 17.1 to 24.76 µm (average 20.39 ± 1.906 µm) in length and 5.4 to 6.61 µm (average 6.19 ± 0.434 µm) in width. The DNA of nine isolates were extracted by Ezup Column Bacteria Genomic DNA Purification Kit, and their sequences were identical, so they were named QM1. The internal transcribed spacer (ITS) region, translation elongation factor 1-α (TEF1), and ß-tubulin (TUB2) genes were amplified with primer pairs ITS1/ITS4, TEF1-728F/TEF1-986R and ßt2a/ßt2b (Slippers et al. 2004), respectively. The BLAST analysis indicated that ITS (OR215464), TEF1 (OR243689), and TUB2 (OR243688) of the isolate QM1 were 99 to 100% identical to those of Botryosphaeria dothidea (GenBank accession nos. MH329646 for ITS sequences; OL891702 for TEF1 sequences; MK511445 for TUB2 sequences). In addition, the phylogenetic tree based on sequences from ITS, TEF1 and TUB2 was constructed with MEGA 11 by use of the maximum likelihood method with 1,000 bootstrapping iterations. Based on the multi-locus phylogeny and morphological features, the isolate QM1 was identified as B. dothidea. To test the Koch's postulates, ten leaves from three healthy two- to three-year-old A. japonica plants were surface disinfested with 75% ethanol for 30 s, rinsed with ddH2O three times. The leaves were wounded with a sterile needle and inoculated with 2ml drop of the isolate QM1 conidial suspension (106 spores/mL), with sterile distilled water as a control. All plants were placed in a greenhouse at 28°C, >70% relative humidity and 12 h light/day. The experiment was repeated three times. After 7 days, leaves of the inoculated group showed symptoms similar to those observed on the naturally infected leaves, while leaves of the control group remained asymptomatic. The pathogen was reisolated from inoculated leaves and was confirmed as B. dothidea based on morphological and molecular analyses. It has been reported B. dothidea cause leaf disease in a wide range of hosts in China, such as Camellia oleifera (Hao et al. 2023), Kadsura coccinea (Su et al. 2021). To our knowledge, this is the first report of Botryosphaeria dothidea causing leaf blight on Aucuba japonica in Zhejiang Province of China. B. dothidea are usually secondary invaders and are known to cause diseases in stressed plants. The results further expand the host-range of B. dothidea, and would help to establish control strategy against the disease.

First Report of Leaf Blight of Osmanthus fragrans Caused by Diaporthe eres in China.

Osmanthus fragrans is an evergreen garden tree species, with high ecological, social, and economic benefits (Lan et al. 2023), which is widely planted in Guizhou Province. From late April to June 2023, a leaf blight disease was observed on O. fragrans in a bauxite mining area in Qingzhen City, with an incidence of ~50%. Symptoms first appeared at the leaf tip or margin, as irregular brown spots, which gradually coalesced into dark brown patches until the leaves withered and fell off. Symptomatic leaves were collected and surface disinfected with 2% NaClO for 30 s, 75% ethanol for 30 s, rinsed 3 times in sterile ddH2O, air-dried and placed on potato dextrose agar (PDA) medium and incubated at 25°C for 7 d. Fungal colonies on PDA of 9 similar obtained isolates were white, with at least one concentric ring. The reverse was light yellow and gradually turned brown. At 12 d, the pycnidia on PDA was gray to black, spherical or conical, with a diameter of 305.15 µm (n=20). The conidial horns oozed out from pycnidia after 25 d of incubation on Pinus massoniana needles. The alpha conidia were unicellular, fusiform, hyaline, had a guttule at each end, and measured 6.24 ± 0.10 µm × 2.48 ± 0.04 µm (n=50). No beta or gamma conidia were observed. The morphological characteristics were likely to Diaporthe spp. (Gomes et al. 2013). DNA of isolates GH02, GH06 and GH08 was extracted. The internal transcribed spacer region (ITS) and partial sequences of translation elongation factor 1-alpha (TEF1-α), calmodulin (CAL), beta-tubulin (TUB2), and histone H3 (HIS) genes were amplified with primers ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R, CAL228F/CAL737R (Carbone and Kohn, 1999), ßt2a/ßt2b and CYLH3F/H3-1b (Crous et al. 2004; Glass and Donaldson, 1995), respectively. The sequences of ITS, TEF-1α, TUB2, CAL and HIS were deposited in GenBank (GH02: PP813499, PP813844, PP813846, PP813848 and PP813850; GH06: PP813500, PP813845, PP813847, PP813849 and PP813851; GH08: PP507168 and PP529956 to PP529959). BLAST results showed the sequences of GH08 were highly identical to sequences of Phomopsis mahothocarpi (NR147522 [ITS], 527/530), P. mahothocarpi (MW700277 [TEF-1α], 367/372), D. eres (OR885862 [TUB], 513/513), D. celeris (ON221721 [CAL], 484/486), and D. eres (OP968956 [HIS], 477/477). A phylogenetic tree constructed with MEGA X using Neighbor-Joining algorithm (Felsenstein, 1985) indicated the isolate GH02, GH06 and GH08 separated from D. eres CBS 297.77 previously reported from O. aquifolium in Netherlands, as well as D. osmanthi and D. fusicola from O. fragrans in China (Gomes et al. 2013; Long et al. 2019; Si et al. 2021). Based on these results, the three isolates were identified as D. eres (Chaisiri et al., 2021). The isolate GH08 was deposited in the Forest Protection Laboratory, Guizhou University. To confirm pathogenicity, spore suspensions (1×105 spores/mL) of GH08 were sprayed on healthy detached leaves (n=10) and leaves of 3-year-old potted O. fragrans seedlings (n=8). An equal volume of sterile water was sprayed for the control. Then they were placed at 20°C and 70-80% RH. Similar leaf blight symptoms appeared after 5 and 15d on the inoculated leaves and seedlings, respectively. The re-isolated fungus, was identical to D. eres based on morphological and molecular analysis, thus fulfilling Koch's postulates. To our knowledge, this is the first report of D. eres causing leaf blight of O. fragrans in China, supporting a basis for developing effective methods to manage this disease.

First Report of Diaporthe hongkongensis Causing Leaf Blight on Macadamia in China.

Macadamia (Macadamia ternifolia Maiden and Betche) belongs to the Proteaceae family (Li et al. 2022). In the hilly areas of Guangxi (southern China), macadamia trees are an important source of revenue. The planting area in Guangxi has increased in recent years, exceeding 53,333 hectares by the end of 2022, but this increase is also associated with emergency of, macadamia diseases. Leaf blight symptoms were observed in 37/241 macadamia trees (15% incidence) in a plantation in Nanning, Guangxi province in China, during June, 2022. Disease severity on infected trees ranged from 5% to 60%. The disease developed from the tips or margins of leaves, causing the leaves to turn brown, and later gradually withered (Fig. 1 A). Ten leaves with lesions were collected from five macadamia trees (two leaves per tree. Thereafter, small segments (3 to 4 mm²) excised from the margins of ten lesions were surface sterilized in 75% ethanol for 30 s and 1% hypochlorite for 90 s and Page 1 of 6 2 rinsed in sterile water, before plating onto potato dextrose agar (PDA) medium. Plates were incubated under lighting during the daytime, and darkness at night-time for 5 days at 25℃. Twenty-two purified colonies were generated by subculturing hyphal tips, of which eight exhibited similar morphology and were further characterized. The colonies on PDA were gray with a white outer ring and flat lawn on the surface (Fig. 1 B). The pycnidia were superficial to semi-immersed on PDA, solitary to aggregated, globose to sub-globose, brown to black and oozed yellow mucilaginous masses (Fig.1 C). The α-conidia were unicellular, hyaline elliptical or fusiform, and measuring 4-8 × 1.9-4 µm (n=30) ， whereas the ß-conidia were hyaline, long, straight or curved, measuring 20-23 × 0.9-2 µm (n=30) (Fig. 1 D-E). The morphological features were similar to Diaporthe hongkongensis (Dissanayake et al. 2015). The eight morphologically similar isolates were identified as D. hongkongensis using the internal transcribed spacer (ITS) region, but only one isolate, JG11, was selected for further molecular identification. Five target genes, including the ITS region, translation elongation factor 1 alpha (EF1-α), beta-tubulin genes (TUB2), calmodulin (CAL), and histone H3 (HIS) were amplified and sequenced using primers ITS1/ITS4, EF1-728F/EF1-986R, Bt2a/Bt2b, CAL-228F/CAL-737R, and CYLH3F/H3-1b, respectively (Carbone and Kohn 1999). The sequences were deposited in GenBank under accession numbers OQ932790 (ITS) and OR147955-58 for EF1-α, TUB, CAL and HIS genes, respectively. BLAST search of GenBank showed that ITS, EF1-α, TUB, CAL, and HIS sequences of JG11 were similar to Page 2 of 6 3 those of D. hongkongensis NR111848 (99.22% identity), KY433566 (99.72%), MW208603 (99.42%), MW221740 (99.80%), and MW221661 (99.79%), respectively. Phylogenetic analysis of concatenated sequences was performed with IQ-TREE software. JG11 was grouped in the same clade as other Diaporthe hongkongensis isolates (Fig. 2). Pathogenicity experiments were carried out on healthy macadamia trees in a greenhouse. Three macadamia trees were used as negative controls where five uninjured leaves per tree were sprayed with sterile distilled water. Uninjured five leaves per tree of three other macadamia trees were sprayed with conidia suspension of the isolate JG11 at a concentration of 1×106. Each treatment was repeated 3 times independently, with 5 leaves per tree (Liu et al. 2023; Havill et al. 2023; Zhang et al. 2022). Plastic bags were placed over all inoculated leaves. The average daily temperature and relative humidity in the greenhouse were 32°C and 65%, respectively. Two days later, browning appeared on the leaves inoculated with the spore suspension and expanded outward. After 5 days, all macadamia leaves inoculated with the fungal spores began to wither, while controls remained asymptomatic (Fig. 1 H-I). D. hongkongensis was consistently re-isolated and purified from inoculated leaves and the identity was confirmed by morphological identification and molecular analysis, completed Koch's postulates. D. hongkongensis has been reported on peach (Zhang et al. 2021), grapevine trunk (Dissanayake et al. 2015) and Cunninghamia lanceolata (Liao et al. 2022). To our knowledge, this is the first report of D. hongkongensis causing leaf blight on macadamia in China. These findings provide a foundation for future research on the epidemiology and control of this newly emerging disease of macadamia.

First Report of Leaf Blight of Camellia japonica Caused by Diaporthe fukushii in Tennessee and the United States.

Japanese camellia (Camellia japonica), is an important ornamental species that has an increasing economic value in China, Japan, Australia and the USA (Vela et al. 2013). Leaf blight symptoms were observed on 20-year-old C. japonica 'April Tryst' leaves collected from a research plot in McMinnville, TN in March 2022. Leaf blight first appeared in the leaf tips and was irregular in shape (2 to 3 cm in diameter). Affected areas displayed gray color discoloration with a deep black margin and gradually expanded in size along the leaf margin, eventually causing leaf death and defoliation. Dark brown globose to subglobose conidiomata (pycnidia) were observed abundantly on the infected leaves (Fig. 1a). Disease severity was 25 to 50% of leaf area and incidence was 10% out of 60 plants. Three leaves were collected from each symptomatic plant and the surface disinfected with 10% NaOCl for 60 s, washed thrice with distilled water, and plated on potato dextrose agar (PDA). Colony growth of the isolates FBG4744 and FBG6184 on PDA, 15 days after incubation at 25°C (light/dark: 12/12h) were white to pale grey with dense and felted mycelium with concentric zonation. Spherical black pycnidia were observed on the concentric rings 2-3 weeks after incubation. Alpha conidia were on average 7.15 × 4.82 µm (4.89 to 9.37 µm × 2.91 to 6.74 µm) in size and were aseptate, hyaline, smooth, and ellipsoidal (n=50). Beta conidia were not observed. Pathogen identity was confirmed by extracting total DNA using the DNeasy PowerLyzer Microbial Kit from 7-day-old cultures. Primer pairs ITS1/ITS4 (White et al. 1990), T1/T222 and EF1/EF2 (Stefanczyk et al. 2016) were used to amplify and sequence the ribosomal internal transcribed spacer (ITS), beta-tubulin (BT), and translation elongation factors 1-α (EF1-α) genetic markers, respectively. The sequences (GenBank accession nos. OR607729, ITS; OR608485, BT; OR608487, EF1-α) were 100% similar to Diaporthe fukushii (=Phomopsis fukushii) in the NCBI nr/nt database (JQ807450: ITS; MG812590: BT, and MG281573: EF1-α). A phylogenetic analysis was performed using concatenated sequences of ITS, BT, and EF1-α of D. fukushii and other closely related taxa retrieved from GenBank (Fig. 2). Pathogenicity tests were performed on 1-year-old 10 healthy potted plants of C. japonica 'April Tryst' per isolate (Mathew et al. 2015; Yang et al. 2019). One leaf per plant was wounded with a sterilized 0.2-mm needle. PDA plugs (5 mm) taken from 7-day old cultures of FBG4744 and FBG6184 isolates were deposited on the wounded leaves and covered with moist cotton (Yang et al. 2019; Zhao et al. 2020). Ten additional plants were used as control and sterile PDA plugs were placed on the wounded leaves. Plants were covered with clear plastic bags and kept inside a greenhouse at 21 to 23°C, 70% RH, 16 h photoperiod. All inoculated leaves exhibited blight symptoms 14 days after inoculation (Fig. 1b) while control plants remained asymptomatic (Fig. 1c). The pathogen was reisolated from all the inoculated leaves and was confirmed as D. fukushii using morphological and molecular tools. Diaporthe species (D. tulliensis, D. passiflorae and D. perseae) have been previously reported to cause leaf spot on Camellia sinensis in Taiwan (Ariyawansa et al. 2021), but to our knowledge, this is the first report of leaf blight of C. japonica caused by Diaporthe fukushii in Tennessee and the United States. Identification of this novel disease is important in developing necessary management approaches.

First report of leaf blight caused by Nigrospora hainanensis on Euonymus japonicus in China.

Euonymus japonicus Thunb., belonging to the family Celastreace and native to East Asia, is a widely cultivated evergreen ornamental woody plant with important ecological and economic values. In May 2023, serious leaf blight of E. japonicus occurred in the campus green space at Guiyang University, Guizhou Province, China (26°55'85"N, 106°78'04"E). Early symptom appeared as small, circular light brown spots on the edges or tips of the leaves. Then, the spot developed visible necrosis, initially light brown to dark brown halos with clear margins. Subsequently, severely infected leaves appear totally wilt, and significantly decrease their ornamental values. In a 0.07-ha field, the disease incidence reached to 40-55%. To identify the pathogen, ten typical symptomatic E. japonicus leaves were collected. They were initially immersed in 75% ethanol for 3 min, and by sodium hypochlorite (4% NaClO) solution for 45 s, and ultimately rinsed with sterile distilled water (dH2O) five times for not less than 1 min each time, then, placed the leaves on potato dextrose agar (PDA) medium and cultured for 5 days at 25°C in constant temperature incubator. Cultures were purified to yield eight isolates. Early colonies are white and regularly rounded, gradually turning dark brown to black with fluffy mycelium. Conidia were single celled, smooth, black, spherical or ellipsoidal. The conidia size of the representative strain, GY-2 and GY-3, was averagely 12.3-17.3 µm × 10.8-17 µm (n = 50). The conidiogenous cells were monoblastic, hyaline, globose or ampulliform. Morphology-based identification revealed the strain as Nigrospora spp. (Wang et al., 2017). For further confirmation, PCR of GY-2 and GY-3 DNA was performed with the primers ITS1/ITS4 (White et al., 1990), Bt2a-F/Bt2b-R (Glass and Don-aldson 1995), and TEF1-728F/TEF1-986R (Carbone and Kohn 1999). Sequences of the ITS region, TUB and TEF1 genes from the strain GY-2 and GY-3 were deposited in GenBank. (GY-2: OR999377, PP112221 and PP150467; GY-3: PP406871, PP421045 and PP421046, respectively). BLAST analysis showed GY-2 100%, 100%, and 98.36%; GY-3 99.43%, 98.21% and 100% (ITS region, TEF1, and TUB) identity to N. hainanensis sequences (accession numbers. NR_153480.1, KY019415.1, and KY019464.1; KX986094.1, OP611475.1, and KY019597.1). Additionally, tandem sequences of ITS, TUB and TEF1 constructed by MEGA 7.0 confimed the homology through the phylogenetic tree. Pathogenicity tests were conducted on healthy plants grown, each 5 mm diameter of active growing mycelium plug of isolate GY-2 was attached to 15 leaves from five healthy 2-year-old E. japonicu plants. The same number of leaves in the control group were treated with non-inoculated plugs only. All the plants were incubated at 25°C and 75% relative humidity with a 16-h/8-h photoperiod. After 10 days, no symptoms appeared on the leaves of the control group. In contrast, symptomatic blight appeared on all leaves inoculated with GY-2. Pathogenicity tests were performed five times. Pure strains were re-isolated from diseased leaves and, confirmed to be N. hainanensis based on the above methods. Recently, Nigrospora oryzae was reported as causal agent of leaf spots on Euonymus japonicus in China (Xu et al., 2023). To our knowledge, this study is the first report of N. hainanensis causing leaf blight on E. japonicu. Identification of the etiological agent may provide assistance for sustainable management in the future.

Unravelling Species Diversity and Pathogenicity of Fusarium spp. Associated with Soybean Leaf and Root in Heilongjiang Province, China.

Soybean (Glycine max L.) holds significant global importance and is extensively cultivated in Heilongjiang Province, China. Soybean can be infected by Fusarium species, causing root rot, seed decay, stem rot, and leaf blight. In 2021 to 2022, a field survey of soybean diseases was carried out in 11 regions of Heilongjiang Province, and 186 soybean leaves with leaf blight symptoms and 123 soybean roots with root rot symptoms were collected. Unexpectedly, a considerable number of Fusarium isolates were obtained not only from root samples but also from leaf samples. A total of 584 Fusarium isolates (416 from leaves and 168 from roots) were obtained and identified as 18 Fusarium species based on morphological features and multilocus phylogenetic analyses with tef1 and rpb2 sequences. Fusarium graminearum and Fusarium sp. 1 in FOSC were the dominant species within soybean leaf and root samples, respectively. Pathogenicity tests were conducted for all Fusarium isolates on both soybean leaves and roots. Results showed that F. graminearum, F. ipomoeae, F. citri, F. compactum, F. flagelliforme, F. acuminatum, and F. sporotrichioides were pathogenic to both soybean leaves and roots. F. solani, F. avenaceum, F. pentaseptatum, F. serpentinum, F. annulatum, and Fusarium sp. 1 in FOSC were pathogenic to soybean roots, not to leaves. To our knowledge, this is the first study to thoroughly investigate soybean-associated Fusarium populations in leaves and roots in Heilongjiang Province.

Characterization of QoI-Fungicide Resistance in Cercospora Isolates Associated with Cercospora Leaf Blight of Soybean from the Southern United States.

Cercospora leaf blight (CLB) of soybean, caused by Cercospora cf. flagellaris, C. kikuchii, and C. cf. sigesbeckiae, is an economically important disease in the southern United States. Cultivar resistance to CLB is inconsistent; therefore, fungicides in the quinone outside inhibitor (QoI) class have been relied on to manage the disease. Approximately 620 isolates from plants exhibiting CLB were collected between 2018 and 2021 from 19 locations in eight southern states. A novel polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay based on two genes, calmodulin and histone h3, was developed to differentiate between the dominant species of Cercospora, C. cf. flagellaris, and C. cf. sigesbeckiae. A multilocus phylogenetic analysis of actin, calmodulin, histone h3, ITS rDNA, and transcription elongation factor 1-α was used to confirm PCR-RFLP results and identify remaining isolates. Approximately 80% of the isolates collected were identified as C. cf. flagellaris, while 15% classified as C. cf. sigesbeckiae, 2% as C. kikuchii, and 3% as previously unreported Cercospora species associated with CLB in the United States. PCR-RFLP of cytochrome b (cytb) identified QoI-resistance conferred by the G143A substitution. Approximately 64 to 83% of isolates were determined to be QoI-resistant, and all contained the G143A substitution. Results of discriminatory dose assays using azoxystrobin (1 ppm) were 100% consistent with PCR-RFLP results. To our knowledge, this constitutes the first report of QoI resistance in CLB pathogen populations from Alabama, Arkansas, Kentucky, Mississippi, Missouri, Tennessee, and Texas. In areas where high frequencies of resistance have been identified, QoI fungicides should be avoided, and fungicide products with alternative modes-of-action should be utilized in the absence of CLB-resistant soybean cultivars.

First Report of Alternaria alternata Causing Leaf Blight on Elsholtzia ciliata in China.

Elsholtzia ciliata is an annual medicinal plant characterized to the family Lamiaceae Martinov. It is grown in most parts of China and has high economic value as a traditional Chinese medicine. In September of 2022, E. ciliata plants located at the planting base of traditional Chinses medicine in Daying county (30°35'40″N, 105°14 12″E), Sichuan Province, China, were recorded with leaf blight. The incidence of symptomatic plants was 15% (30 infected plants out of 200 surveyed). The symptoms included an irregular necrotic lesion at the tip of the leaf, which gradually expanded across the entire leaf. To elucidate the cause of the symptoms, 12 symptomatic leaves were sampled from four different plants and 5×5 mm section, including symptomatic and non-symptomatic tissue was excised. Tissue samples were disinfected in 75% ethanol for 30s, and 7% sodium hypochlorite for 1 min, and then rinsed three times with sterile distilled water (Sun et al. 2022). The sampled tissues were placed onto potato dextrose agar (PDA) and incubated at 25℃ in the dark. Seven days later, single spores were recovered onto fresh PDA (Zhu et al. 1992). Colonies on PDA initially appeared white, developing grayish-green conidia with white margins. Conidia (n=150) were collected and observed under the microscope. The conidia were smooth walled and dark brown, with pear-shaped, 12.1-31.4 × 5.0-9.4µm, with 3-5 transverse septa, 1-3 longitudinal or oblique septa. Conidiophores were thick, dark brown, simple with multiple conidial scars, 5.0-75.5 × 2.5.0-5.0µm. Based on morphological observations the 12 isolates were most similar to Alternaria alternata (Simmons 2007). The internal transcribed spacer (ITS) rDNA regions, glyceraldehyde-3-phosphate dehydrogenase (gpd), Alternaria major allergen (Alt a 1), RNA polymerase second largest subunit gene (RPB2) and translation elongation factor 1-alpha (TEF 1) were amplified and sequenced using the primers ITS4/ITS5, RPB2-5F/RPB2-7CR, gpd1/gpd2, EF1-728F/EF1-986R, and Alt-for/Alt-rev respectively (Woudenberg et al. 2015). The sequences of representative isolate (XR) were uploaded in GenBank (ITS: OM319521, RPB2: OM849248, gpd: OM296240, TEF1: OM238122, and Alt a 1: OM649814). The bootstrap value of the isolate and the type strain CBS 595.93 (ITS: KP124320, RPB2: KP124788, gpd: KP124175, TEF1: KP125096, and Alt a 1: JQ646399) on the phylogenetic tree was 99%. Therefore, based on morphology and phylogenetic analysis the fungus was identified as A. alternata. To verify pathogenicity, a spore suspension (1 × 106 conidia/ml) of the representative isolate XR was misted onto the foliage of six twenty-day-old non-symptomatic plants. Six additional plants were sprayed with distilled water and used as controls. The plants were covered with plastic bags for 48 h and incubated at a temperature of 28℃ in the dark. Eight days later, all inoculated plants demonstrated similar symptoms as recorded on the original source, while the control plants were symptomless. The experiment was repeated three times with similar results. A. alternata was re-isolated from the artificially inoculated plants, hence fulfilling Koch's postulates. To our best knowledge this is the first report of leaf blight caused by A. alternata in China on E. ciliate. The disease may be an economic threat and should be further monitored and studied.

First Report of Achromobacter xylosoxidans Causing Bacterial Stem and Leaf Blight on Cyrilla arida in Tennessee and the United States.

Scrub titi (Cyrilla arida), broadleaf semi-evergreen shrub, is endemic to central Florida. However, its smaller stature, lustrous, dark-green leaves and abundance of white racemes in late spring make it a potential candidate for future use in Southeastern U.S. landscapes. Three-years-old container grown C. arida plants maintained in a shade house at the Nursery Research Center, McMinnville, TN exhibited black leaf lesions and brown stem lesions (Fig. 1a) in April 2023. The disease severity was 25% of the shoot area and the disease incidence was 10% out of 60 plants. Symptomatic stem and leaf tissues were surface sterilized with 0.525% NaOCl for 1 min. Bacterial colonies were white-colored, opaque, round with smooth edges on lysogen broth agar medium after 2 days of incubation at 28°C. Bacteria were gram-negative and non-fluorescent on King's B. Esculin, catalase, and oxidase tests were positive but arginine dihydrolase and gelatine hydrolysis were negative. Bacterial identity was confirmed by sequencing of DNA from pure cultures (strains FBG5290 and FBG5294). The 16S ribosomal RNA, RNA polymerase sigma factor (rpoD), enolase (eno), and NADH-quinone oxidoreductase subunit L (nuoL) genes were amplified and sequenced using the primers 8F/1492R (Galkiewicz et al. 2008), rpoDpF/R (Sarkar and Guttman 2004), enoP1/P2 and nuoLP1/P2 (Spilker et al. 2012), respectively. The sequences were deposited in GenBank with acc. nos.: OR689356, OR689357 (16S); OR751366, OR751367 (rpoD); OR792456, OR792457 (eno); and OR792458, OR792459 (nuoL). The closest identified species to our two identical strains was Achromobacter xylosoxidans (CP054571), showing 99.6%, 95.2%, 96.2%, and 95.0% identity with >99% coverage to the above mentioned gene sequences, respectively. Phylogenetic analysis, using concatenated sequences along with the genome sequences of other closely related taxa (Fig. 2), suggest that A. xylosoxidans is presently the identified species, but given the results of the MLST, it may be that this organism will be classified as new species in the future. The pathogenicity of the strains was confirmed on 1-year-old C. arida by inoculating five plants per strain. Stems were inoculated by depositing 15 µl of bacterial suspension (1x108 CFU/mL) into the stem wounded using a scalpel. The inoculation sites were covered with moist cotton and wrapped with Parafilm. Inoculation was also performed on three leaves per plant by using a needleless syringe to infiltrate bacteria into the intercellular spaces (1x108 CFU/mL). Sterile water was used for five control plants. Plants were kept in a greenhouse at 21-23°C, 70% RH, and 16-h photoperiod. All inoculated plants showed brown lesions in stems (Fig. 1b and 1c) and leaves (Fig. 1d) 7-10 days after inoculation, while control plants remained asymptomatic (Fig. 1e and 1f). The bacteria were re-isolated from inoculated plants and confirmed as A. xylosoxidans using morphological and molecular methods. Achromobacter spp. are commonly known as human pathogens, and cross-kingdom pathogenic bacterium in animal (mice) and fungi (Coprinus comatus) (Ye et al. 2018). However, A. xylosoxidans was recently reported as the causal agent of stem rot of Amorphophallus konjac in China (Wei et al. 2023). To our knowledge, this is the first report of A. xylosoxidans causing bacterial stem and leaf blight of C. arida in Tennessee and the U.S. Identification of this novel disease lays the foundation development of effective management strategies.

First Report of Alternaria alternata Causing Leaf blight on Epimedium sagittatum (Sieb. et Zucc.) Maxim. in China.

Epimedium sagittatum (Sieb.et Zucc.) Maxim. is an important material of traditional Chinese medicine because of the rich content of flavonoids that are used to treat osteoporosis, liver cancer, and sexual dysfunction (Liu et al. 2013). A leaf blight was observed on E. sagittatum in Zhumadian City, China (32°58'12" N, 114°37'48" E, continental monsoon climate) in June 2021. Survey indicated that about 18% of the plants were infected in a 266-ha commercial planting area. The initial symptoms were white patches with tan borders, irregular in outline, with small black particles visible on the center of the lesions. In a week or so, patches extended throughout the leaf, and then leaves withered. Thirty leaves with symptoms collected from five different sites were cut into 5×5 mm pieces, and then surface-sterilized with 75% ethanol for 15 s followed by rinsing with double distilled water (ddH2O) three times. The pieces were then disinfested with 0.1% HgCl2 solution for 30 s, and rinsed with ddH2O, then placed onto potato-dextrose agar medium (PDA) and incubated in the dark for 3 d at 28°C. Eight fungal isolates were purified; of these, only the isolate HY2-1 infected the host plant and was selected for further morphological characterization. The colonies of HY2-1 were olive green with loose aerial hyphae on PDA. Conidiophores were single or branched, producing brown conidia in short chains. Conidia were obclavate, obpyriform, or ellipsoidal, 15.9-47.3 µm × 7.6-16.6 µm (n=50) and pale brown or dark brown with a short cylindrical beak at the tip that contained 1-5 transverse septa and 0-4 longitudinal septa. Morphological characteristics of the isolate were identical with those of Alternaria species (Huang et al. 2022). For molecular identification, the internal transcribed spacers (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (Weir et al. 2012), major allergen Alt a 1(Alt a 1) and translation elongation factor 1-α gene (TEF) (Lawrence et al. 2013) were amplified and sequenced using the primers ITS4/5, GDF/GDR, Alt-F/R, and EF1-728F/986R, respectively. The results of the sequencing were uploaded to GenBank as ITS (OR418487), GAPDH (OR419792), Alt a 1 (OR419794), and TEF (OR419796), respectively. Phylogenetic analyses were performed by concatenating all the sequenced loci using the Bayesian method in Phylosuite (Zhang et al.2020). The phylogenetic tree indicated that the isolate belongs to the A. alternata clade with a bootstrap value of 75%. The pathogen was identified as A. alternata based on the morphological and molecular results. To satisfy Koch's postulates, a conidial suspension (106 conidia/mL) of the HY2-1 was prepared with ddH2O to infect the healthy plants. Ninety healthy leaves on 30 plants in pots were punctured using a sterilized needle, and then inoculated by spraying the conidial suspension on the wounded leaves in a greenhouse at 25°C and 80% relative humidity. The control plants were sprayed with ddH2O. The plants showed similar symptoms to the original infected plant 15 d after inoculation. The controls showed no symptoms. A pure culture of A. alternata was isolated and identified again as previously described. Leaf blight caused by A. alternata has been reported on Taro (Liu et al. 2020), Toona ciliata (Wang et al. 2023), etc. To our knowledge, this is the first report of E. sagittatum leaf blight caused by A. alternata in China. The results will help to develop effective control strategies for leaf blight on E. sagittatum.

Aggressive Alternaria brassicicola with Reduced Fungicide Sensitivity Can Be Associated with Naturally Infested Broccoli Seeds.

Alternaria brassicicola is a part of the Alternaria complex that causes leaf blight and head rot (ABHR) in brassica crops. Infested broccoli seeds can play an important role in introducing A. brassicicola in transplant houses and production fields. However, characterization of natural seed infestation and seed-to-seedling transmission of A. brassicicola in broccoli is yet to be demonstrated. In this research, we characterized Alternaria spp. isolates from commercial broccoli seedlots for their species identity, pathogenicity, and aggressiveness on broccoli and their sensitivity to a quinone-outside inhibitor (QoI) fungicide (azoxystrobin). Two hundred commercial seedlots from two broccoli cultivars, Cultivar 1 (EC; n = 100 seedlots) and Cultivar 2 (ED; n = 100 seedlots) were, evaluated for the presence of A. brassicicola under in vitro conditions using a seedling grow-out assay. Alternaria spp. was detected in 31 and 28% of the commercial seedlots of Cultivar 1 and Cultivar 2, respectively. The seed-to-seedling transmission (%) varied considerably within each positive-infested seedlot, which ranged from 1.3 to 17.3%. Subsequent molecular identification of single-spore cultures (n = 138) was made by sequencing four housekeeping genes: actin, the major allergen (Alta1), plasma membrane ATPase, and glyceraldehyde-3-phosphate dehydrogenase (GPD), and the sequences were concatenated and compared for the phylogenetic distance with diverse Alternaria species. Ninety-six percent (n = 133) of the isolates formed a cluster with a known A. brassicicola based on a multigene phylogeny, which were later confirmed as A. brassicicola using a species-specific PCR assay. One hundred percent of the A. brassicicola seed isolates (n = 133) were either highly or moderately aggressive on broccoli (cultivar Emerald Crown) based on a detached leaf assay. Sensitivity of representative A. brassicicola isolates (n = 58) to azoxystrobin was evaluated using a spore germination assay, and the EC50 values (effective fungicide concentration [ppm] at which germination of conidia of isolates were reduced by 50% compared to control) for each isolate was determined. A. brassicicola isolates from naturally infested commercial broccoli seeds were sensitive to azoxystrobin with considerably low EC50 values in the range of <0.0001 to 0.33 ppm; however, there were a few isolates (14%) that showed 100-fold reduced sensitivity from the most sensitive isolate (EC50 = 0.0001 ppm). Our results confirm that commercial broccoli seedlots can be naturally contaminated with pathogenic and aggressive A. brassicicola. We also provide evidence for the potential presence of A. brassicicola isolates with reduced azoxystrobin-sensitivity in naturally infested commercial broccoli seedlots, which has never been reported before. Together, these findings may have implications in considerations for seed-health testing, seed treatments, and greenhouse scouting to limit introduction of infested seedlots in commercial broccoli fields.

First report of Pseudomonas cichorii causing bacterial leaf blight of pocketbook plant (Calceolaria hybrida) in Taiwan.

Pocketbook plants (Calceolaria spp.) are flowering ornamentals often grown as potted plants (Poesch 1937). In December 2022, leaf blight symptoms were observed on 2-mo-old plants of C. hybrida F1 'Dainty'. The disease was found in a nursery in Ren'ai Township, Nantou, and about 20% of the plants exhibited symptoms. Symptomatic plants had brown or gray necrotic lesions of different sizes and shapes, mostly around leaf margins. Lower leaf wilting was also observed (Fig. S1, A and B). Three plants were sampled. Leaf lesions were surface-disinfected with 75% ethanol and cut into smaller pieces in 10 mM MgCl2. After observing bacterial streaming under a microscope, the bacteria were streaked onto nutrient agar (NA). Following 2 days at 28°C, a type of round, creamy white colony predominated on all the plates. Three strains (Calc-A, Calc-B, and Calc-C) were obtained, one from each plant. The strains produced fluorescent pigments on King's B medium and were tested Gram-negative. The strains were characterized with the LOPAT scheme (Schaad et al. 2001). They did not exhibit activities of pectic enzymes, arginine dihydrolase and levan sucrase, but produced oxidase and induced the hypersensitive response in tobacco. DNA was extracted from the strains for PCR amplification of the 16S rDNA with primer pair 27f/1492r as described by Lane (1991). The 16S rDNA sequences were compared with entries in the GenBank database. The sequences obtained (GenBank accession no. OR824302) matched that of Pseudomonas cichorii MAFF 301158 (accession no. AB724288; 1,403/1,403 bp) and were 99% identical to that of DSM 50259T (accession no. CP074349; 1,391/1,405 bp). The strains were also tested with the species-specific primers hrp1a and hrp2a (Cottyn et al. 2011). The amplicons were sequenced and a BLASTn search showed that the sequences (accession no. OR827305) shared the highest identity (99.3%) with that of P. cichorii strain 83-1 (accession no. DQ168848; 848/854 bp) and were 97.3% identical to the sequence of DSM 50259T (accession no. CP074349; 831/854 bp). Calc-A was selected as a representative strain and deposited in the Bioresource Collection and Research Center, Taiwan (reference no. BCRC 81432). Koch's postulates were fulfilled by spray-inoculating a suspension of Calc-A on three 2-mo-old C. hybrida F1 'Dainty' plants. The inoculum was prepared by suspending NA-grown cells in 10 mM MgCl2 including 0.02% Silwet L-77 (OD600 = 0.3; 1.5 x 108 CFU/ml). For the controls, three plants were sprayed with bacteria-free solution. The plants were bagged throughout the experiment and kept in a growth chamber (14/10 h light/dark; 26/24°C day/night). Leaf blight and wilting symptoms developed on all leaves of the inoculated plants after 30 h, but not the controls (Fig. S1, C and D). The pathogen was reisolated from the treatment group, and colony PCR with hrp1a/hrp2a showed that the reisolated strain shared the same sequence with Calc-A to Calc-C. Repeating the inoculation assay produced consistent results. This is the first report of P. cichorii affecting Calceolaria in Taiwan. The bacterium has been reported infecting diverse crops in Taiwan, such as tomato and lettuce (Tsai et al. 2014). Expanding the understanding of the pathogen's potential hosts could help prevent its spread across important crops.

Introgression of blast and bacterial blight disease resistance genes in a rice genotype ADT43 through marker assisted back cross breeding.

Bacterial Leaf Blight (Xanthomonas oryzae pv. oryzae) and blast (Magnaporthe oryzae) are the major biotic stresses around the rice-growing zones of the world. The development of resistant varieties through Marker Assisted Backcross Breeding is the utmost economical and eco-friendly method for achieving stable yield. Amongst the resistance genes recognized, Xa21 and Pi54 possess broad-spectrum resistance to many Xoo and blast strains around the world. In the present study, we have effectively introgressed a Bacterial Blight resistance gene (Xa21) and a blast resistance gene (Pi54) into susceptible variety ADT43 from RP-Bio-Patho-2 coupled with phenotypic selection for agronomic, cooking quality and grain traits through MABC. MABC was sustained till BC2F2 generation with specific markers pTA248 for Xa21 and Pi54MAS for Pi54 resistance genes. A set of SSR markers for parental polymorphism were utilized for maximum regaining of recurrent parent genome in each backcrossing. "Positive plants" from BC2F1 were selfed to generate BC2F2 and the homozygous lines for bacterial leaf blight and blast resistance genes were identified for further assessment.

Genome Sequence Resource of a Colletotrichum graminicola Field Strain from China.

The maize anthracnose stalk rot and leaf blight diseases caused by the fungal pathogen Colletotrichum graminicola is emerging as an important threat to corn production worldwide. In this work, we provide an improved genome assembly of a C. graminicola strain (TZ-3) by using the PacBio Sequel II and Illumina high-throughput sequencing technologies. The genome of TZ-3 consists of 36 contigs with a length of 59.3 Mb. After correction and evaluation with the Illumina sequencing data and BUSCO, this genome showed a high assembly quality and integrity. Gene annotation of this genome predicted 11,911 protein-coding genes, among which 983 secreted protein-coding genes and 332 effector genes were predicted. Compared with previous genomes of C. graminicola strains, TZ-3 genome is superior in nearly all parameters. The genome assembly and annotation will enhance our knowledge of the genetic makeup of the pathogen and molecular mechanisms underlying its pathogenicity and will provide valuable insights into genome variation across different regions. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Bulk segregant analysis coupled with transcriptomics and metabolomics revealed key regulators of bacterial leaf blight resistance in rice.

BACKGROUND: Bacterial leaf blight (BLB) is a highly destructive disease, causing significant yield losses in rice (Oryza sativa). Genetic variation is contemplated as the most effective measure for inducing resistance in plants. The mutant line T1247 derived from R3550 (BLB susceptible) was highly resistant to BLB. Therefore, by utilizing this valuable source, we employed bulk segregant analysis (BSA) and transcriptome profiling to identify the genetic basis of BLB resistance in T1247. RESULTS: The differential subtraction method in BSA identified a quantitative trait locus (QTL) on chromosome 11 spanning a 27-27.45 Mb region with 33 genes and 4 differentially expressed genes (DEGs). Four DEGs (P < 0.01) with three putative candidate genes, OsR498G1120557200, OsR498G1120555700, and OsR498G1120563600,0.01 in the QTL region were identified with specific regulation as a response to BLB inoculation. Moreover, transcriptome profiling identified 37 resistance analogs genes displaying differential regulation. CONCLUSIONS: Our study provides a substantial addition to the available information regarding QTLs associated with BLB, and further functional verification of identified candidate genes can broaden the scope of understanding the BLB resistance mechanism in rice.