First Report of Diaporthe tectonendophytica Causing Leaf Spot on Dalbergia odorifera in Guangxi, China.

Dalbergia odorifera T. Chen (Family: Fabaceae) is a national level II protected plant in China, with extremely high economic value and medical properties (Zhao et al. 2020). In June 2023, an unknown leaf spot was found in a garden land of Pingxiang city, Guangxi, China, and approximately 80% of the plants covered an area of 500 m2 displayed similar symptoms. The spots were grey to white, 4~6 mm in diameter (n=30) with black pycnida on the spots surface (Fig S1, A-D). Multiple disease spots were observed on a single leaf. The pycnida on the lesion were picked and mashed, to make a conidia suspension using sterile water. The conidial solution was then spread onto a potato dextrose agar (PDA) plate containing streptomycin, with 10 mg of streptomycin per 100 mL, and incubated for 3 days at 28°C with a 12 hour photoperiod. Three isolates (GXPX01, GXPX02 and GXPX03) were obtained by re-culturing the colonies on fresh PDA plates. The colony on PDA were white with aerial mycelia (Fig S1, E-F). Black conidiomata developed at 28°C with a 12 hour photoperiod in 20 days (Fig S1, G-H). Alpha conidia were 4.2~6.4 µm × 1.8~2.6 µm (average =5.1 × 2.3 µm, n = 30), mostly bi-guttulate, hyaline, ellipsoid, apex bluntly rounded, base obtuse to subtruncate, smooth (Fig S1, I). Beta conidia were 15.1~33.5 µm × 1~1.8 µm (average = 24.5 × 1.5 µm, n = 30), filiform, hyaline, curved or hamate, aseptate, base subtruncate (Fig S1, J). Morphological characteristics of the three isolates matched those of Diaporthe spp.(Gomes et al. 2013). The rDNA internal transcribed spacer (ITS) region, the translation elongation factor 1-α (TEF1), the calmodulin (CAL), the histone H3 (HIS) and the ß-tubulin (TUB2) genes of the three isolates were amplified using the primer pairs ITS4/ITS5, EF1-728F/EF1-986R, CAL-228F/CAL2Rd, CYLH3F/H3-1B, and T1 /CYLTUB1R, respectively (Crous et al. 2004, Sun et al. 2021). The sequences were all deposited in GenBank (accession numbers OR437511 to OR437513 for ITS, OR454965 to OR454967 for TEF1, OR454968 to OR454970 for CAL, OR454971 to OR454973 for TUB2, OR454974 to OR454976 for H3). Sequences had 98.36% to 100% homology with the corresponding sequences of known Diaporthe tectonendophytica strains MFLUCC 13-0471 in the NCBI database. Phylogenetic analysis was based on combined ITS, TEF1, TUB2 and CAL sequences data using MEGA 11 software to construct phylogenetic tree with Maximum Likelihood (Doilom et al. 2017). In the phylogenetic tree, the combined sequences attributed the three isolates to the D. tectonendophytica (Fig S2). The pathogenicity was tested on leaves of 1.5-year-old D. odorifera seedlings. Three leaves were wounded with a sterile needle and individually inoculated with a 5 mm mycelial disk of PDA culture from each isolate. Sterile PDA disks inoculated leaves as a control. The test was repeated three times. The inoculated plants were placed in a greenhouse at 25℃ and 90% humidity, with a photoperiod of 12 hours. Five days after inoculation, necrotic lesions appeared on inoculated leaves and symptoms from all three isolates were the same as those form natural infections ( Fig S1, K-N), whereas all the control remained symptomless (Fig S1, P). The pathogen was reisolated from the inoculated leaves and again identified as D. tectonendophytica, with the same methodology used for the initial identification. D. tectonendophytica was reported to cause plant diseases, such as stem gray blight of red-fleshed dragon fruit (Hylocereus polyrhizus) (Rahim et al. 2021), leaf spots disease on Elaeagnus conferta and Pometia pinnata (Sun et al. 2021). To our knowledge, this is the first report of D. ctonendophytica causing leaf spot disease on D. odorifera.

First Report of Stem and Leaf Blight Disease on Mesona chinensis Caused by Rhizoctonia solani in China.

Mesona chinensis is an important medicinal and edible plant resource distributed in eight provinces in southern China. In December 2021, an unknown stem and leaf blight disease was found in M. chinensis cultivation areas in Longzhou County, Guangxi, China. Sixty days after transplanting, the incidence of this disease was 10%. Leaf spots mostly appeared from the leaf edge, were irregular, brown to dark brown, causing more than half of the leaf or the whole leaf to die. The infected stem first showed dark brown spots, then constricted slightly, became necrotic and rotted with the expansion of the spots, resulting in the death of the whole plant. Loose cobweb-like mycelia, which resembled Rhizoctonia, could be seen on the diseased tissues in conditions of high humidity. To identify the pathogen, diseased stems and leaves with typical symptoms from Longzhou County were collected and surface-sterilized with 75% ethanol for 30 s. Small fragments (5×5 mm) at the junction of diseased and healthy tissues were disinfected with 1% NaClO for 1min, washed with sterile water three times, transferred to potato dextrose agar (PDA), and incubated at 28°C for 3 days. Mycelial tips were removed, and six isolates (No. R1-R6) were obtained. The colonies were initially gray white and later light brown. Many nearly round to irregular sclerotia appeared after 7 days of culture. The sclerotia turned from light brown to deep brown and were 1 to 5 mm in diameter. The mycelium branched at a 90° angle, with septa near the branches and a constriction of the mycelium at the base of the branch. These morphological characteristics were consistent with Rhizoctonia. For molecular identification, genomic DNA of the six isolates was obtained using an extraction kit (Biocolor, Shanghai, China), and primers ITS4/ITS5 were used to amplify the internal transcribed spacers (ITS) and 5.8S rRNA (White et al. 1990). A 750 bp DNA fragment was obtained and the sequences were deposited in GenBank (OM095383-OM095388). All isolates had ≥ 99% identity with anastomosis group AG1-1B (HG934429 and HQ185364) of R. solani. A phylogenetic tree showed that the isolates and those from anastomosis group AG1-1B clustered into one branch. To satisfy Koch's postulates, the isolates from diseased leaf (No. R1, R2, and R3) and diseased stem (No. R4, R5, and R6) were inoculated on leaves and stems of 45-day-old M. chinensis plants. Five leaves and stems were inoculated with mycelial plugs of each isolate without wounding and another five leaves and stems were inoculated with mycelial plugs of each isolate after pinprick wounding. Control wounded leaves and stems were inoculated with sterile PDA discs. To maintain high humidity, the plants were incubated at 28°C and covered with transparent plastic covers. Diseased spots first appeared 24 h after inoculation. Three days post-inoculation, all inoculated leaves and stems showed symptoms like those observed in the field, whereas controls were asymptomatic. The pathogen was re-isolated from the diseased inoculated tissues using the method described above, and isolated fungi had the morphological characteristics of R. solani. Thus, the pathogen causing stem and leaf blight disease of M. chinensis was determined to be R. solani. The host range of R. solani is wide, and anastomosis group AG1-1B has been reported to infect plants such as rice, bean, fig, cabbage, and lettuce (Sneh et al. 1991). To our knowledge, this is the first report of R. solani causing a stem and leaf blight on M. chinensis, and provides a basis for diagnosis and control of the disease.

First report of leaf spot caused by Colletotrichum siamense on Michelia alba in China.

Michelia alba (common name: white champaca), native to Indonesia, is a preciously ornamental and medicinal plant in the west and southeast of China and widely distributed in Nanning, Guangxi, China (Hou et al. 2018). In May 2020, a foliar disease of M. alba was observed in Nanning (22°51' N; 108°17' E), Guangxi, China, present on ca. 20-30% of the leaves. The disease began to develop from the margins of leaves in most cases. The symptoms recorded were light yellow spots, which gradually developed into ellipsoidal to irregular brown spots, surrounded by a wide yellow halo. The spots gradually enlarged in size and became grey-brown, with the dimension of 3.5 × 2.8 to 11.0 × 3.5 cm, even more than half of leaf area. In the later stage of infection, these spots coalesced resulting in necrosis and early shedding of the leaves. Sometimes black acervuli were observed on some lesions. For isolation of the fungus, ten symptomatic leaves were randomly sampled from five trees and washed with sterile water. Small pieces of infected tissue (about 4 mm2) were surface disinfected in 75% alcohol for 30 s and in 0.1% aqueous solution of mercury chloride for 1 min. Finally these tissue pieces were rinsed three times with sterile water, plated on potato dextrose agar (PDA) and then incubated for 7 days at 28℃ with a photoperiod of 12 h. Fifteen strains with similar morphological characterizations were isolated, and five representative isolates (BL-1 to BL-5) were purified. These cultures gave rise to grey-white colonies with bright orange conidial masses with contained one-celled, hyaline, guttulate conidia, measuring 12.68-20.70 × 4.27-7.84 µm (average 15.36 × 5.35 µm, n=100). Appressoria formed from conidia were brown, ellipsoidal or inverted trapezoid and measured 6.36-12.13 × 5.07-7.39 µm (average 8.29 × 6.36 µm, n=30). These morphological characteristics were similar to those of the Colletotrichum gloeosporioides species complex (Weir et al. 2012). To confirm identification, genomic DNA from mycelium of these five isolates was extracted, and the sequence of internal transcribed spacer (ITS), chitin synthase (CHS-1), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), actin (ACT), calmodulin (CAL) and ß-tubulin (TUB2) were amplified (Zhang et al. 2020), and the GenBank accession numbers for the sequences were MW186173 to MW186177 (ITS), MW161290 to 161294 (CHS-1), MW161295 to MW161299 (GAPDH), MW161285 to 161289 (ACT), MW084710 to 084714 (CAL) and MW161300 to MW161304 (TUB2). The phylogenetic tree of six combined genes of the five isolates clustered with Colletotrichum siamense strains (CBS 125378, ICMP 17795 and ICMP 18121). Therefore, the isolates were identified as C. siamense. Five isolates (BL-1 to BL-5) were tested for pathogenicity. Wounded and unwounded detached healthy leaves were inoculated using mycelial discs (5 mm in diameter) and conidial suspensions (with the concentration of 1 × 105 conidia/ml) at the same time, incubated in a growth chamber at 25-30℃ (85-90% relative humidity, with a photoperiod of 12 h). Three leaves (wounded left half blade and unwounded right half blade) were inoculated with different methods for each isolate, and the tests were repeated three times. Four days after inoculation, leaf spots were observed on all wounded leaves, while 5-10% of the unwounded leaves showed lesions. Control leaves inoculated with PDA discs and sterile water remained symptomless. Colletotrichum. siamense was re-isolated from the lesions, confirming Koch's postulates. At least 60 plant species have been reported to be infected by C. siamense worldwide (Ji et al. 2019). To our knowledge, this is the first report of C. siamense causing leaf spot on M. alba in China.