First report of anthracnose fruit rot of papaya caused by Colletotrichum gigasporum in China.

Papaya (Carica papaya L.) belonging to the family Caricaceae is well known for its economic and nutritional value. Anthraconse caused by Colletotrichum spp. is a main postharvest disease of papaya fruit during storage (Cia et al., 2007). In July 2022, papaya fruits with anthracnose symptoms were collected in Changjiang County (108.996180E, 19.246560N), Hainan Province, China. The disease incidence of fruit rot reached 6.3%. Initial symptoms appeared as the watery lesions with tiny black spots, turning to dark brown, sunken necrotic lesions. The diseased tissues were cut into 18 pieces (5×5 mm) from 6 papaya fruits, disinfected with 2% sodium hypochlorite for 60 s, and rinsed three times with sterilized water. The pieces were air-dried and then placed on potato dextrose agar (PDA) at 28 ℃ for five days. Twelve isolates with similar morphology were obtained from 18 tissue pieces. Three isolates (FMG01, FMG02 and FMG03) were selected for morphological identification, molecular identification, and pathogenicity tests. Colonies were initially white, then gradually became dark grey on PDA. The ascospores were hyaline, fusoid, rounded at both ends, 37.43-84.32 (55.79±7.61) µm × 4.30-6.55 (5.36±0.60) µm (n=50). The conidia were hyaline, unicellular, long cylindrical, bluntly rounded at both ends, 11.59-25.54 (18.62±2.33) µm × 5.12-8.44 (7.19±0.62) µm (n=100). Appressoria were gray to dark brown, irregular, pyriform, or ovoid, 10.14-21.40 (13.81±2.25) µm × 6.05-11.85 (9.16±1.29) µm (n=50). Morphological features are similar to Colletotrichum gigasporum identified and described by Rakotoniriana et al (Rakotoniriana et al., 2013). In order to accurately identify the isolates, the internal transcribed spacer region (ITS) of the rDNA, the glyceraldehyde-3-phosphate dehydrogenase (GAPDH), the partial actin (ACT), the beta-tubulin (TUB2) and the calmodulin (CAL) genes were amplified and sequenced (Cannon et al., 2012). The nucleotide sequences were deposited into GenBank (accession numbers, ITS: OR017446 to OR017448, GAPDH: OR042810 to OR042812, ACT: OR042813 to OR042815, TUB2: OR042816 to OR042818, CAL: OR042819 to OR042821). Based on the BLASTn analysis, these sequences were more than 99% with the reference strain CBS 125476 of C. gigasporum sequences (ITS: MH863698, GAPDH: KF687833, ACT: KF687790, TUB2: KF687875, CAL: KF687814), respectively. The results of the multilocal phylogenetic analysis showed that the three isolates were C. gigasporum based on the Maximum Likelihood and Bayesian inference method. The pathogenicity test was performed by wounded with a sterile needle on the surface-sterilized papaya fruits. The mycelial discs (5 mm diameter) of three isolates were inoculated orderly on the same fruit, and the same inoculation was applied to non-wound papaya fruits. The control group were inoculated with sterilized PDA. Each treatment carried out with 9 fruits. The inoculated fruits were placed at 28 ℃ in plastic preservation boxes (32×22×11 cm) with sterilized distilled water to maintain high humidity. After 5 d of inoculation, typical anthracnose symptoms were observed on wound fruits and the non-wound fruits developed symptoms at 7 dpi, control fruits were symptomless. The fungi re-isolated from the inoculated fruits lesions after inoculation and identified by morphological characterization and molecular identification, fulfilling Koch's postulates. C. gigasporum has been reported causing leaf rot of Dalbergia odorifera in China (Wan et al., 2018). To our knowledge, this is the first report of anthracnose fruit rot of papaya caused by C. gigasporum in China.

First report of anthracnose caused by Colletotrichum karstii on Dalbergia odorifera in China.

Dalbergia odorifera (Family: Fabaceae) is a national second-grade protected tree in China with high medicinal and economic value (Zhao et al., 2020). In July, 2022, a leaves spot disease on D. odorifera with typical anthracnose symptoms was observed in plantations in Haikou (110.319153°E, 19.072900°N), Dongfang (108.630297°E, 19.103838°N) and Qiongzhong (109.704460°E, 19.088440°N), Hainan Province, China. Disease incidence was 7.5% (n = 50 plants). Early symptoms of infected leaves were small and round dark brown spots, which developed into larger irregular necrotic lesions and leaves withered. Leaf tissues (5×5 mm) at the disease-health junction of spots from 19 leaves were sterilized with 2.5% sodium hypochlorite for 1 min, and rinsed with sterile distilled water three times. These sterilized tissues were placed on potato dextrose agar (PDA) and incubated at 28 ℃ for 5 d. 7 strains of fungi with similar morphology were isolated, and 3 single-hyphal isolates (HHL01, HHL02 and HHL03) from each location were selected for further study. Colonies on PDA were fluffy orange-yellow mycelium. Conidia were aseptate, cylindrical, smooth-walled, straight, hyaline with both ends bluntly rounded, 11.82 to 15.77 × 3.87 to 6.71 µm (n = 100; average = 13.75 × 5.52 µm). Appressoria formed on slides, measured 5.54 to 10.64 × 4.19 to 7.41 µm (n = 30; average = 8.06 × 5.97 µm) were brown to black, elliptical to irregular. For molecular biological identification, the genomic DNA of three isolates was extracted by fungal genomic DNA extraction kit (Tiangen Biotech (Beijing) Co., Ltd.). The partial sequences of internal transcribed spacer region (ITS; ITS1/ITS4), glyceraldehyde-3-phosphate dehydrogenase (GAPDH; GDF1/GDR1), actin (ACT; ACT512F/ACT783R), ß-tubulin (TUB2; TI/Bt2b) and calmodulin (CAL; CL1C/CL2C) were amplified and sequenced by Sangon Biotech (Shanghai) Co., Ltd (Carbone and Kohn, 1999; Weir et al., 2012). The sequences were deposited as GenBank Accession Nos. OR018110-OR018112 (ITS); OR050529-OR050537 (GAPDH, ACT and CAL) and OR192168-OR192170 (TUB). BLASTn results showed these sequences were more than 99% identity with the strain of C. karstii CORCK1 (GenBank Accession Nos. HM585406, HM585387, HM581991, HM585424 and HM582010, respectively). Multi-locus phylogenetic tree of Colletotrichum spp. showed that those three isolates were sister to C. karstii based on the maximum likelihood and bayesian inference methods. To verify pathogenicity, 2 mL spore suspension (1 × 106conidia/ml) of the isolates was sprayed on each leaves of 1-year-old D. odorifera plants, and sterile distilled water was similarly sprayed on other leaves as a negative control. The plants were incubated in a greenhouse under 90% ± 5% RH at 28 °C. Light brown small round necrotic patches developed 3 days after inoculation, while the control was asymptomatic. Photographs were taken on the fifth day after inoculation. The fungi were re-isolated from the diseased leaves and identified by morphological characterization and molecular identification, fulfilling Koch's postulates. C. karstii has been reported causing leaf rot of Carissa grandiflora in Spain (Garcia-Lopez et al., 2021), and anthracnose caused by C.tropicale was reported on D. odorifera (Yi et al., 2023). To our knowledge, this is the first report of Dalbergia odorifera leaf spot disease caused by Colletotrichum karstii. This finding provides an important basis for further research on the control of the disease.

First report of stem-end rot caused by Botryosphaeria fabicerciana on mango fruits in China.

Mango (Mangifera indica L.), belongs to the family Anacardiacea, and is one of the most popular tropical fruits in the world. Stem-end rot is a major postharvest disease of mango fruit, causing severe losses during storage in China (Chen et al., 2015). In July 2021, the mango fruits harvested from Baise Municipal National Agricultural Science and Technology Park (23.683568 N, 106.986325 E) of Guangxi province in China developed stem-end rot during storage. The disease incidence reached ca. 8.3%. The initial symptoms appeared as light brown lesions surrounding the peduncle, which quickly expanded becoming large dark-brown lesions. Small pieces of epidermis (5 mm × 5 mm) from 8 typical diseased friuts were cut from the edges of lesions surface-sterilized with 2% sodium hypochlorite and rinsed with sterile distilled water. The tissue was plated on potato dextrose agar (PDA) and incubated at 28 ℃ in the dark for 3 days. Fifteen, similarcolonies were isolated from the symptomatic tissue. The representative isolates DF-1, DF-2 and DF-3 were selected for morphological characterization, molecular identification, and pathogenicity testing. The colonies were circular with fluffy aerial mycelium, initially white turning to smoke-gray from the center in upper side and greenish black in reverse side, covering the 90 mm diameter Petri dish after 4 days of incubation on PDA at 28 ℃ in dark. Pycnidia were produced on the surface of the colony after 30 days. Conidia were fusiform, aseptate, hyaline, thin-walled with granular contents, apex sub-obtuse, base subtruncate to bluntly rounded, 14.0-20.3 (16.8±1.6) µm × 3.1-7.2 (5.1±0.9) µm (n=50). The sexual stage was absent. Based on morphology, isolates were preliminarily identified as Botryosphaeria speices. To accurately identify the pathogen, genomic DNA was extracted from the mycelium of the three isolates DF-1, DF-2 and DF-3. The internal transcribed spacer of rDNA region (ITS), elongation factor 1-alpha (EF-1α) and beta-tubulin gene (TUB) genes were amplified using primers ITS1/ITS4, EF1-728F/EF1-986R and Bt2a/Bt2b, respectively (Slippers et al., 2004). The nucleotide sequences were all deposited in GenBank (ITS: OP729176-OP729178 EF-1α: OP758194-OP758196 and TUB: OP758197-OP758199). Based on the BLASTn analysis, the ITS, EF1-α and TUB sequences of three isolates were 100%, 99% and 99% similar to the Botryosphaeria fabicerciana MFLUCC 10-0098 sequences (ITS: JX646789, EF-1α: JX646854 and TUB: JX646839). Multi-locus phylogenetic analyses (ITS, EF-1α and TUB) showed that the isolate DF-1, DF-2 and DF-3 were clustered within Botryosphaeria fabicerciana clade based on the maximum likelihood , Bayesian inference, and maximum parsimony methods. The pathogenicity test was performed by placing discs mycelium around the peduncle of mature mango fruits by pin-prick method. Each treatment carried out with 12 fruits. The inoculated fruits were placed in plastic boxes at 28 ℃ with three replicates. Three days after inoculation, typical symptoms of stem-end rot were observed. The control fruits were inoculated with sterile PDA discs, and remained symptomless. The same fungus was re-isolated from the symptomatic tissue to complete Koch's postulate. Botryosphaeria fabicerciana (basionym: Fusicoccum fabicercianum) was first reported as pathogen causing senescent twig of Eucalyptus spp. in China (Chen et al., 2011; Phillips et al., 2013). To our knowledge, this is the first report of Botryosphaeria fabicerciana causing stem-end rot of Mangifera indica in China.

First report of Neofusicoccum sinoeucalypti causing leaf spot on Terminalia catappa in China.

Terminalia catappa belonging to the family Combretaceae, spreads in tropical and subtropical coastal areas. It mainly serves as shading and decorative tree (Anand et al, 2015). It is planted as roadside tree in Southern China. A leaf spot disease of T. catappa was observed at Wencheng Town (110.805323°E, 19.524567°N), Wenchang City, Hainan province, China in June, 2022. The disease incidence of leaves reached 10%. The occurrence of this leaf spot would reduce the ornamental value of T. catappa. The early symptoms of infected leaves were small, round, dark brown spots surrounded by irregular light halos, developing to larger irregular necrotic lesions and leaves withered. Twelve diseased leaves were collected from three survey trees. Symptomatic leaf samples were collected and cut into small pieces (3×3 mm). The pieces were surface sterilized with 2.5% sodium hypochlorite for 1 min, rinsed with sterile distilled water three times, placed on potato dextrose agar (PDA) medium and incubated at 28 ℃ in the dark for 3 days. Three hyphal tip isolates (DYLR-1, DYLR-2 and DYLR-3) were cultured on PDA. Colonies on PDA reached the edge of the 90 mm plates after 3 d and had fluffy mycelia with an uneven margin, initially creamy white, becoming light grey (5 d) to mouse grey (10 d) at the surface with the black globular cavity. To induce sporulation, the isolates were transferred to 2% water agar media with sterilised pine needles placed on the surface of the media. Conidia was hyaline, unicellular, thin-walled, smooth with granular contents, aseptate, narrowly fusiform, base subtruncate to bluntly rounded, 11.1 to 16.7 (14.5±1.4) × 4.6 to 7.6 (6.2±0.7) µm (n=50). Spermatia was hyaline, unicellular, aseptate, allantoid to rod-shaped, 3.2 to 6.9 (5.1±0.9) µm × 2.0 to 3.8 (2.5±0.4) µm (n=50). Pathogenicity tests were performed both in vitro and in vivo, and replicated twice. All three isolates were used for pathogenicity tests, with 18 detached leaves used for pathogenicity tests in vitro and 3 seedlings used for pathogenicity tests in vivo. A 5-mm-diameter agar plug containing mycelia were placed on the leaves both without and with wound. Sterile PDA plugs were used as controls. The leaves were moisturized with a clear plastic bag for 24 hours in a greenhouse under 90% ± 5% RH at 25 ℃. Brown spot symptoms were observed at 1 day post-inoculation (dpi) in vitro and 3 dpi in vivo. The same strains were reisolated from lesions of inoculated leaves. Control plants were symptomless. For molecular identification, internal transcribed spacer region and intervening 5.8S nrRNA gene (ITS; ITS1/ITS4 primers; White et al. 1990), translation elongation factor 1-alpha gene (tef1-α; EF1-728F/EF1-986R primers; Carbone and Kohn 1999), beta-tubulin gene (tub2; Bt2a/Bt2b primers; Glass and Donaldson 1995) and DNA directed RNA polymerase II second largest subunit gene (rpb2; RPB2bot6F/RPB2bot7R; Sakalidis et al. 2011) regions were PCR amplified from genomic DNA. The sequences (GenBank accessions numbers: OP435357 to OP435359 of ITS; OP535354 to OP535356 of tef1-α; OP535351 to OP535353 of tub2; OP535348 to OP535350 of rpb2) had 100%, 99.7%, 100%, 100% similar to the type strain of Neofusicoccum sinoeucalypti CERC2005 (GenBank accessions numbers: KX278061, KX278166, KX278270 and KX278290), respectively. Multi-locus phylogenetic tree (ITS, tef1-α, tub2 and rpb2) of Neofusicoccum spp. (Zhang et al. 2021) showed that those three isolates were sister to N. sinoeucalypti based on the maximum likelihood and bayesian inference methods. N. sinoeucalypti was first reported pathogen causing from Eucalyptus plantations and adjacent plants in China (Li et al. 2018). To our knowledge, this is the first report of Neofusicoccum sinoeucalypti causing leaf spot disease on Terminalia catappa in China. Neofusicoccum species, commonly cause diseases in woody plants worldwide, and identification of this pathogen is important for effective disease management and control.

Genome-wide transcriptome analysis uncovers gene networks regulating fruit quality and volatile compounds in mango cultivar 'Tainong' during postharvest.

Mango is one of the most economically important fruit; however, the gene regulatory mechanism associated with ripening and quality changes during storage remains largely unclear. This study explored the relationship between transcriptome changes and postharvest mango quality. Fruit quality patterns and volatile components were obtained using headspace gas chromatography and ion-mobility spectrometry (HS-GC-IMS). The changes in mango peel and pulp transcriptome were analyzed during four stages (pre-harvesting, harvesting, maturity, and overripe stages). Based on the temporal analysis, multiple genes involved in the biosynthesis of secondary metabolites were upregulated in both the peel and pulp during the mango ripening process. Moreover, cysteine and methionine metabolism related to ethylene synthesis were upregulated in the pulp over time. Weighted gene co-expression network analysis (WGCNA) further showed that the pathways of pyruvate metabolism, citrate cycle, propionate metabolism, autophagy, and SNARE interactions in vesicular transport were positively correlated with the ripening process. Finally, a regulatory network of important pathways from pulp to peel was constructed during the postharvest storage of mango fruit. The above findings provide a global insight into the molecular regulation mechanisms of postharvest mango quality and flavor changes.

Novel Insight into the Relationship between Metabolic Profile and Fatty Acid Accumulation Altering Cellular Lipid Content in Pineapple Fruits at Different Stages of Maturity.

Pineapple fruits are usually harvested at different stages of maturity, based on consumer demands. The stage of maturity significantly affects the storage tolerance due to alterations in the cellular lipid homeostasis in the fruits. The characteristic abundance of metabolites and fatty acids (FAs) can provide vital information giving insight into the cellular lipid changes that occur during the ripening process in the fruits. Here, liquid chromatography-tandem mass spectrometry, largely based on the analysis of widely targeted metabolomics, was applied to evaluate the differences in the metabolites among the pineapple at three different stages of maturity namely, pineapples at the young fruit (YF), mature fruit (MF), and fully mature fruit (FMF) stages. In this study, 466 metabolites were annotated and identified. Among these, 59 lipids, including the glyceride esters, fatty acids and conjugates, and lysophospholipids (LPLs) were characterized. Notably, the LPLs were down-regulated in their relative abundance in the MF compared with the YF, and subsequently they remained almost stable in the FMF stage. The FA profiling results revealed the presence of certain unsaturated fatty acids (UFAs); besides, the total monounsaturated fatty acid (MUFA) to saturated fatty acid (SFA) ratio, as well as the polyunsaturated fatty acids (PUFA) to SFA ratio, showed noticeable decrease during the ripening process. The differential accumulation patterns of the LPLs, MUFAs, PUFAs, and SFAs imply that the lipid degradation and peroxidation take place in the pineapple fruits from the YF to MF and YF to FMF stages, respectively. The present study provides new insights into the alterations in the cellular lipid metabolism underlying the metabolite profiles and accumulation of FAs in pineapple fruits during ripening.

First report of Fusarium incarnatum causing fruit rot of litchi in China.

Litchi (Litchi chinensis Sonn.) is an indigenous tropical and subtropical fruit in Southern China with an attractive appearance, delicious taste, and good nutritional value (Jiang et al. 2003). In March 2020, brown rots were observed on nearly ripe litchi fruits (cv. Guihuaxiang) in an orchard of Lingshui county, Hainan province of China (18.615877° N, 109.948871° E). About 5% fruits were symptomatic in the field, and the disease caused postharvest losses during storage. The initial infected fruits had no obvious symptoms on the outer pericarp surfaces, but appeared irregular, brown to black-brown lesions in the inner pericarps around the pedicels. Then lesions expanded and became brown rots. Small tissues (4 mm × 4 mm) of fruit pericarps were cut from symptomatic fruits, surface-sterilized in 1% sodium hypochlorite for 3 min, rinsed in sterilized water three times, plated on potato dextrose agar (PDA) and incubated at 28℃ in the darkness. Morphologically similar colonies were isolated from 85% of 20 samples after 4 days of incubation. Ten isolates were purified using a single-spore isolation method. The isolates grown on PDA had abundant, fluffy, whitish to yellowish aerial mycelia, and the reverse side of the Petri dish was pale brown. Morphological characteristics of conidia were further determined on carnation leaf-piece agar (CLA) (Leslie et al. 2006). Macroconidia were straight to slightly curved, 3- to 5-septates with a foot-shaped basal cell, tapered at the apex, 2.70 to 4.43 µm × 18.63 to 37.58 µm (3.56 ± 0.36 × 28.68 ± 4.34 µm) (n = 100). Microconidia were fusoid to ovoid, 0- to 1-septate, 2.10 to 3.57 µm × 8.18 to 18.20 µm (2.88 ± 0.34 × 11.71 ± 1.97 µm) (n = 100). Chlamydospores on hyphae singly or in chains were globose, subglobose, or ellipsoidal. Based on cultural features and morphological characteristics, the fungus was identified as a Fusarium species (Leslie et al. 2006). To further confirm the pathogen, DNA was extracted from the 7-day-old aerial mycelia of three isolates (LZ-1, LZ-3, and LZ-5) following Chohan et al. (2019). The sequences of the internal transcribed spacer region of rDNA (ITS), translation elongation factor-1 alpha (tef1) gene, and histone H3 (his3) gene were partially amplified using primers ITS1/ITS4, EF1-728F/EF1-986R, and CYLH3F/CYLH3R, respectively (Funnell-Harris et al. 2017). The nucleotide sequences were deposited in GenBank (ITS: 515 bp, MW029882, 533 bp, MW092186, and 465 bp, MW092187; tef1: 292 bp, MW034437, 262 bp, MW159143, and 292 bp, MW159141; his3: 489 bp, MW034438, 477 bp, MW159142, and 474 bp, MW159140). The ITS, tef1, and his3 genes showed 99-100% similarity with the ITS (MH979697), tef1 (MH979698), and his3 (MH979696) genes, respectively of Fusarium incarnatum (TG0520) from muskmelon fruit. The phylogenetic analysis of the tef1 and his3 gene sequences showed that the three isolates clustered with F. incarnatum. Pathogenicity tests were conducted by spraying conidial suspension (1×106 conidia/ml) on wounded young fruits in the orchid. Negative controls were sprayed with sterilized water. Fruits were bagged with polythene bags for 24 hours and then unbagged for 10 days. Each treatment had 30 fruits. The inoculated fruits developed symptoms similar to those observed in the orchard and showed light brown lesions on the outer pericarp surfaces and irregular, brown to black-brown lesions in the inner pericarps, while the fruits of negative control remained symptomless. The same fungus was successfully recovered from symptomatic fruits, and thus, the test for the Koch's postulates was completed. F. semitectum (synonym: F. incarnatum) (Saha et al. 2005), F. oxysporum (Bashar et al. 2012), and F. moniliforme (Rashid et al. 2015) have been previously reported as pathogens causing litchi fruit rots in India and Bangladesh. To our knowledge, this is the first report of Fusarium incarnatum causing litchi fruit rot in China.

Inhibition of downy blight and enhancement of resistance in litchi fruit by postharvest application of melatonin.

Litchis are tasty fruit with economic importance. However, the extreme susceptibility of harvested litchis to litchi downy blight caused by Peronophythora litchii leads to compromised quality. This study aimed to study the effects of melatonin on postharvest resistance to P. litchii in 'Feizixiao' litchis. Results showed that melatonin restricted lesion expansion in litchis after P. litchi inoculation. Melatonin enhanced the activities of phenylalanine ammonia-lyase, cinnamate-4-hydroxylase and 4-hydroxycinnamate CoA ligase while promoting the accumulations of phenolics and flavonoids. Nicotinamide adenine dinucleotide phosphate content and glucose-6-phosphate dehydrogenase and 6-phosphogluconic acid dehydrogenase activities were higher in treated fruit than control fruit. Higher energy status along with elevated H+-ATPase, Ca2+-ATPase, succinate dehydrogenase and cytochrome C oxidase activities were observed in treated fruit. Ultrastructural observation showed reduced damage in mitochondria in treated fruit. The results suggest that melatonin induced resistance in litchis by modulating the phenylpropanoid and pentose phosphate pathways as well as energy metabolism. .

First report of Cercospora cf. citrulina causing leaf spot of Ipomoea pes-caprae in China.

Ipomoea pes-caprae plays an important role in protecting the tropical and subtropical coastal beach of the world. In 2018, a leaf spot was observed on I. pes-caprae in Xisha islands of China, 13.2-25.8% of leaves were infected. The initial symptoms were small (1-3 mm diameter), single, circular, dark gray spots with a light-yellow center on the leaves. The lesions enlarged and were scattered or confluent, distinct and circular, subcircular or irregular, occasionally vein-limited, pale to dark gray-brown, with a narrow dark brown border surrounded by a diffuse yellow margin. Microscopic observations of the spots revealed that caespituli were dark brown and amphigenous, but abundant on the underside of the leaves. Mycelia were internal. Conidiophores were fasciculate, occasionally solitary, pale olivaceous-brown throughout, 0- to 3-septate, 27.9-115.8 (63.4±22.5) µm × 3.2-5.3 (4.3±0.87) µm (n=100). Conidial scars were conspicuously thickened. Conidia were solitary, hyaline, filiform, acicular to obclavate, straight to slightly curved, subacute to obtuse at the apex, truncate at the base, multi-septate, 21.0-125.5 (60.2±20.1) µm × 2.0-5.0 (3.8±0.83) µm (n=100). Single-conidium isolates were obtained from representative colonies grown on potato dextrose agar (PDA) incubated at 25℃ in the dark. The colonies grew slowly and were dense, white to gray and flat with aerial mycelium. Mycelia were initially white, and then became gray. Conidia were borne on the conidiophores directly. The pure isolate HTW-1 was selected for molecular identification and pathogenicity test, which were deposited in Microbiological Culture Collection Center of Environment and Plant Protection Institute, Chinese Academy of Tropical Agricultural Sciences. The internal transcribed spacer (ITS) region of rDNA, translation elongation factor 1-alpha (tef1) and histone H3 (his3) genes were amplified with ITS1/ITS4, EF-1 / EF-2, and CYLH3F / CYLH3R primers, respectively (Groenewald et al. 2013). The obtained sequences of HTW-1 were all deposited in GenBank with accession numbers MT410467 for ITS, MT418903 for tef1 and MT418904 for his3. The ITS, tef1 and his3 genes all showed 100% similarity for ITS (JX143582), tef1 (JX143340) and his3 (JX142602) with C. cf. citrulina (MUCC 588; MAFF 239409) from I. pes-caprae in Japan. Based on the morphological characteristics and molecular identification, the pathogen was identified as Cercospora cf. citrulina (Groenewald et al. 2013). The pathogenicity test was conducted by spraying conidial suspension (1×104 conidia/mL) on wounded and unwounded leaves for seedling of I. pes-caprae in greenhouse and in sterile vitro condition. The conidial suspension was prepared using conidia from 30-day-old culture grown on PDA at 25℃ in the dark. Leaf surfaces of seedling in greenhouse were wounded by lightly rubbing with a steel sponge and detached leaf surfaces were wounded by sterile needles. the treatments were sprayed with conidial suspensions on wounded and unwounded leaf surfaces. The control was sprayed with sterile water. After eight days, the typical symptoms of spots which were small, single, circular and dark gray appeared on the inoculated wounded leaves, while the inoculated unwounded leaves and the control leaves were symptomless. The pathogen was only re-isolated from the inoculated wounded leaves. The pathogen may be infected by wound. A total of 20 Cercospora and related species was found on Ipomoea spp. (García et al. 1996). Cercospora cf. citrulina has been reported on I. pes-caprae in Japan, although it was unclear if it was a pathogen or saprophyte (Groenewald et al. 2013). To our knowledge, this is the first report of C. cf. citrulina causing leaf spot of I. pes-caprae in China. This disease could threat the cultivation of I. pes-caprae in China.

First report of Colletotrichum siamense causing anthracnose on Erythrina crista-galli in China.

Erythrina crista-galli L. (Fabaceae) is a popular ornamental plant in tropical and subtropical regions of South Asia. In October 2019, anthracnose-like lesions were observed on the leaves of E. crista-galli planted in Haikou, China. 5-30% of leaves were infected. At first, the circular spots of 1-2 mm in diameter were reddish-brown on the leaves, and then enlarged to circular, subcircular or irregular spots with reddish-brown center and surrounded by a diffuse yellow margin. Neighboring spots sometimes coalesced. Under continuously wet or humid conditions, the lesions expanded quickly, and became gray, subcircular or irregular spots covered by grayish-white mycelium and orange-pink conidial masses. Diseased leaves eventually fell off the trees. To identify the pathogen, diseased leaves were sampled from four gardens. Leaf tissues (5×5 mm) were cut from the margins of typical symptomatic lesions, surface-sterilized in 1% sodium hypochlorite for 1 min, plated on potato dextrose agar (PDA) medium, and incubated at 28.0±0.5℃ in the dark. Similar fungal colonies were obtained from all plated tissues after 3 days. The single-conidium colonies of all isolates were white to pale gray and cottony with visible orange conidial masses. Conidia were one-celled, aseptate, hyaline, straight, cylindrical to fusiform with obtuse ends, and ranged from 14.2-18.6 µm (16.4 µm)× 3.8-5.4 µm (4.7 µm) (n=100). After germination, conidia formed single, brown, oval or slightly irregular appressoria ranging from 8.0 to 11.8 µm (9.6 µm), and from 4.8 to 6.0 µm (5.4 µm). Sexual stage was absent. These characteristics of conidia and appressoria were matched with C. siamense belonging to the C. gloeosporioides complex (Prihastuti et al. 2009; Yang et al. 2009; Weir et al. 20012; Hu et al. 2015). To accurately identify the species, DNA was extracted from four purified isolates (JG-1, JG-3-1, SWS-1-3, SWS-2-1) （Fu et al. 2019）. The internal transcribed spacer of rDNA region (ITS), glyceraldehydes-3-phosphate dehydrogenase (GAPDH), calmodulin (CAL), actin (ACT) and chitin synthase (CHS) genes were amplified and sequenced. The nucleotide sequences were all deposited in GenBank (ITS: MT229427-MT229430, GAPDH: MT250821-MT250824, CAL: MT258893-MT258896, ACT: MT258897-MT258900 and CHS: MT258901-MT258904). Multi-locus phylogenetic analyses (ITS, GAPDH, CAL, ACT and CHS) (Weir et al. 2012) showed that the four isolates were clustered with C. siamense, which was in accordance with BLAST results. Pathogenicity tests of the four isolates were repeated three times on detached leaves (Ji et al. 2019). The conidial suspension (1×106 conidia/mL) was prepared using the conidia from 10-day-old cultures grown on PDA. Two 20-µL drops of conidial suspension were inoculated on non-wounded young healthy leaves, and each isolate was inoculated on 10 leaves. Two 20-µL drops of sterile water were inoculated on non-wounded young healthy leaves as control. The samples were maintained in containers at a relative humidity of 90± 5 per cent inside and 28℃ with a 12-h photoperiod. Gray, subcircular spots similar to the field disease symptoms were observed on the all inoculated leaves after 7 days, whereas no visible symptoms appeared on the non-inoculated leaves. The pathogen was re-isolated from inoculated leaves thus fulfilling Koch's postulates. C. gloeosporioides has been previously reported as a pathogen causing leaf spot on Erythrina (E. indica var. picta, E. variegata var. orientalis) in Guam in 1983 and Brazil in 2012. (Russo et al. 1983; Oliveira et al. 2012). To our knowledge, this is the first report of C. siamense causing leaf spot of E. crista-galli in China.

Melatonin Enhances Cold Tolerance by Regulating Energy and Proline Metabolism in Litchi Fruit.

Melatonin (MLT) is a vital signaling molecule that regulates multiple physiological processes in higher plants. In the current study, the role of MLT in regulating chilling tolerance and its possible mechanisms in litchi fruit during storage at ambient temperatures after its removal from refrigeration was investigated. The results show that the application of MLT (400 µM, dipping for 20 min) to 'Baitangying' litchi fruit effectively delayed the development of chilling injury (CI) while inhibiting pericarp discoloration, as indicated by higher chromacity values (L*, a*, b*) and anthocyanin levels. MLT treatment suppressed the enhancements of the relative electrical conductivity (REC) and malondialdehyde (MDA) content, which might contribute to the maintenance of membrane integrity in litchi fruit. MLT treatment slowed the decline in cellular energy level, as evidenced by higher adenosine triphosphate (ATP) content and a higher energy charge (EC), which might be ascribed to the increased activities of enzymes associated with energy metabolism including H+-ATPase, Ca2+-ATPase, succinate dehydrogenase (SDH), and cytochrome C oxidase (CCO). In addition, MLT treatment resulted in enhanced proline accumulation, which was likely a consequence of the increased activities of ornithine-δ-aminotransferase (OAT) and Δ1-pyrroline-5-carboxylate synthase (P5CS) and the suppressed activity of proline dehydrogenase (PDH). These results suggest that the enhanced chilling tolerance of litchi fruit after MLT treatment might involve the regulation of energy and proline metabolism.

Correction to: Analysis of the complete genomic sequence of a novel virus, areca palm necrotic spindle-spot virus, reveals the existence of a new genus in the family Potyviridae.

The original version of this article unfortunately contained a mistake.

Analysis of the complete genomic sequence of a novel virus, areca palm necrotic spindle-spot virus, reveals the existence of a new genus in the family Potyviridae.

A novel virus, tentatively named "areca palm necrotic spindle-spot virus" (ANSSV), was identified in Areca catechu L. in Hainan, China, and its complete genomic sequence was determined. Its positive-sense single-stranded RNA genome is comprised of 9,437 nucleotides (nt), excluding the poly (A) tail, and contains one large open reading frame encoding a polyprotein of 3,019 amino acids (aa). A Blastp search showed that the polyprotein of ANSSV shared a maximum of 31%-32% aa sequence identity (with 86%-95% coverage) with all seven known macluraviruses. Nucleotide sequence comparison of the ORF of ANSSV to those of macluraviruses revealed identities ranging from 41.0% to 44.6%, which is less than the inter-genus identity values for the family Potyviridae. Phylogenetic analysis based on either the aa or nt sequence of the polyprotein did not cluster ANSSV into any established or unassigned genus of the family Potyviridae. Therefore, we suggest that ANSSV is the first member of a previously unrecognized genus of the family Potyviridae.

Delay of Postharvest Browning in Litchi Fruit by Melatonin via the Enhancing of Antioxidative Processes and Oxidation Repair.

Melatonin acts as a crucial signaling and antioxidant molecule with multiple physiological functions in organisms. To explore effects of exogenous melatonin on postharvest browning and its possible mechanisms in litchi fruit, 'Ziniangxi' litchi fruits were treated with an aqueous solution of melatonin at 0.4 mM and then stored at 25 °C for 8 days. The results revealed that melatonin strongly suppressed pericarp browning and delayed discoloration during storage. Melatonin treatment reduced relative membrane-leakage rate and inhibited the generation of superoxide radicals (O2-·), hydrogen peroxide (H2O2), and malondialdehyde (MDA). Melatonin treatment markedly promoted the accumulation of endogenous melatonin; delayed loss of total phenolics, flavonoids, and anthocyanins; and enhanced the activities of antioxidant enzymes, including superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2). By contrast, the activities of browning-related enzymes including polyphenoloxidase (PPO, EC 1.10.3.1) and peroxidase (POD, EC 1.11.1.7) were reduced. In addition, melatonin treatment up-regulated the expression of four genes encoding enzymes for repair of oxidized proteins, including LcMsrA1, LcMsrA2, LcMsrB1, and LcMsB2. These findings indicate that the delay of pericarp browning and senescence by melatonin in harvested litchi fruit could be attributed to the maintenance of redox homeostasis by the improvement of the antioxidant capacity and modulation of the repair of oxidatively damaged proteins.

Effect of postharvest spray of apple polyphenols on the quality of fresh-cut red pitaya fruit during shelf life.

Fresh-cut (FC) red pitaya fruit were treated with 5ga.i.l-1 apple polyphenols (APP) and then stored at 20°C for up to 4days to evaluate the effects on attributes. Results showed that FC pitaya fruit with APP treatment showed greater colour retention, delayed softening, reduced loss of soluble solids content, titratable acidity, betacyanin and total phenolics compared with untreated FC fruit. APP treatment also maintained antioxidant activity, as indicated by higher DPPH radical-scavenging activity and reducing power compared with untreated FC pitaya fruit. APP treatment strongly suppressed microbial growth, contributing to improvement of product safety. Because APP is a natural product, we propose that application of APP could be a convenient, safe and low-cost approach to maintain the quality and extend the shelf life of FC red pitaya fruit.

Low-temperature conditioning induces chilling tolerance in stored mango fruit.

In this study, mango fruit were pre-treated with low-temperature conditioning (LTC) at 12°C for 24h, followed by refrigeration at 5°C for 25days before removal to ambient temperature (25°C) to investigate the effects and possible mechanisms of LTC on chilling injury (CI). The results showed that LTC effectively suppressed the development of CI in mango fruit, accelerated softening, and increased the soluble solids and proline content. Furthermore, LTC reduced electrolyte leakage, and levels of malondialdehyde, O2- and H2O2, maintaining membrane integrity. To reveal the molecular regulation of LTC on chilling tolerance in mango fruit, a C-repeat/dehydration-responsive element binding factor (CBF) gene, MiCBF1, was identified and its expression in response to LTC was examined using RT-qPCR. LTC resulted in a higher MiCBF1 expression. These findings suggest that LTC enhances chilling tolerance in mango fruit by inducing a series of physiological and molecular responses.

Microdochium paspali, a new species causing seashore paspalum disease in southern China.

A new species of Microdochium was identified as the causal agent of leaf blight of seashore paspalum (Paspalum vaginatum), a turf grass widely used in tropical and subtropical golf courses. In 2010 foliar necrosis and canopy thinning were observed on 11 surveyed golf courses in Hainan province, China, especially on fairways and putting greens. The infected leaves initially appeared water-soaked and dark green, rapidly faded to yellow or became chlorotic and quickly died, resulting in a sparse appearance in infected areas, leading to the disease name "sparse leaf patch." Isolates with rich and light pink to yellow mycelia and salmon-colored pionnotes were cultured from diseased turf foliage. Pathogenicity was demonstrated by inoculating these isolates onto "seaspray" seashore paspalum. Phylogenetic analysis based on the nuc rDNA internal transcribed spacer 1-5.8S-internal transcribed spacer 2 region (ITS), translation elongation factor 1-α (TEF1-α) and ß-tubulin (BenA) indicated these isolates formed as a distinct clade within Microdochium (Xylariales). Further microscopic examination demonstrated that the species was morphologically distinct from three similar species of Microdochium. The name Microdochium paspali sp. nov. is proposed for this novel fungal pathogen.