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Pea (Pisum sativum L.) is one of the most important cool season legumes consumed as vegetable in the world. In March 2022, a severe stem rot was observed on pea cultivars in vegetative stage in Wuhan, Hubei Province, China (30°39′ N, 114°66′ E). The infection started on the lower stems, and the lesions were water soaked, then girdled the stem, resulting in wilting of the leaves. Eventually, the entire plant died, and some necrotic stems were covered with gray conidia. To investigate the causal agent, small pieces cut from diseased stems were surface sterilized with 2% NaOCl for 1 min, then incubated on potato dextrose agar (PDA) at 25°C for 3 days. Pure cultures were obtained by hyphal tip transfer and five isolates were studied further. Colonies initially appeared white, turned gray from the center, then became taupe with cottony aerial mycelia, and finally black hard, round or irregular sclerotia (0.92 to 5.34 × 0.86 to 4.42 mm, n = 20) developed. The sealing film of several plates were removed after 5 days, and abundant conidia were produced 3 days later. The conidia are terminally arranged at the end of long, grayish branched conidiophores, conidia are unicellular, hyaline and round or elliptical, (9.2 to 11.4 × 6.7 to 9.2 μm, n = 50), and the conidiophores are (10.7 to 13.0 μm × 760 to 1080 μm, n=20) in size. The morphological characteristics were consistent with descriptions of Botrytis cinerea (Li et al., 2016). Genomic DNA of the five isolates was extracted, and the internal transcribed spacer region (ITS), glyceraldehyde-3-phosphate dehydrogenase (G3PDH) gene, heat-shock protein 60 (HSP60) gene, and DNA-dependent RNA polymerase subunit II (RPB2) gene were amplified using the primers described by Aktaruzzaman et al. (2018). The sequences were deposited in GenBank (accession nos. ON533694 and ON566787-ON566790 for ITS; ON600613 to ON600617 for HSP60; ON600608 to ON600612 for G3PDH; ON600603 to ON600607 for RPB2). The BLASTn analysis of these sequences showed that the isolates had high similarity (99 to 100%) with other B. cinerea isolates. A phylogenetic tree was constructed by MEGA11, and our isolates clustered in the B. cinerea clade. In pathogenicity test, 2-week-old seedlings of pea cultivar ‘Zhongqin1’ were inoculated. Mycelial plugs (5 mm diameter) taken from a 3-day-old colony of each isolate were placed on the axil of a stipule at the 4th node of potted pea plants (n=5 per isolate), and PDA plugs were placed on the same location of control (n=3). Inoculated and control plants were kept in a humid plastic box at 23°C for 2 days, and then placed in a glasshouse. Symptoms with water-soaked lesions were observed on the inoculated plants after 2 days, stems showed soft rot and broke off after 3 to 5 days, disease symptoms similar to those in the field, while the controls remained healthy. The pathogen was re-isolated from the affected stems, fulfilling Koch’s postulates. B. cinerea had been reported to cause foliar, pod, seed and stem rot of pea after flowering in many pea production regions in the world (Kraft and Pfleger, 2001). Pea was recorded as a host of B. cinerea in Zhejiang, Sichuan and Yunnan Provinces (Tai, F. L. 1979; Zhuang, W.-Y. 2005; Zhang, Z. 2006.), but there has been no detailed disease description and identification of pathogen. To our knowledge, this is the first report of B. cinerea causing stem rot on pea in vegetative stage in China. Since B. cinerea can infect pea at any developmental stage, it could have a high economic impact as green pea production increases in China.

Phytophthora vignae is an important oomycete pathogen causing Phytophthora stem rot on some Vigna species. Three P. vignae isolates, obtained from mung bean, adzuki bean and cowpea, respectively, exhibited high similarities in morphology and physiology but are specialized to infect different hosts. Here we reported the first de novo assembly of the draft genomes of three P. vignae isolates, which were performed using the PacBio SMRT Sequel platform. This study will extend the genomic resource available for the Phytophthora genus and provide a good foundation for further research on comparative genomics of Phytophthora species and interaction mechanism between hosts and pathogens.

The gray leaf spots caused by

An emerging soilborne disease resembling Phytophthora stem rot was observed on mung bean plants grown in Anhui, China. To identify the causal agent, diseased plants and soil samples from 13 fields were collected to isolate the pathogen. Twenty-two Phytophthora isolates were recovered from the samples and detailed identification was conducted. Based on morphological and molecular characterizations, all of the isolates were consistently identified as P. vignae. Phylogenetic analysis using eight nuclear loci sequences of the internal transcribed spacer region, rRNA gene large subunit, a partial sequence of the β-tubulin gene, translation elongation factor 1α, 60S ribosomal protein L10, the enolase gene, heat shock protein 90, and triose phosphate isomerase/glyceraldehyde-3-phosphate dehydrogenase and a mitochondrial locus cytochrome c oxidase subunit I revealed that the mung bean isolates grouped in the same clade as P. vignae and its two formae speciales, P. vignae f. sp. adzukicola and P. vignae f. sp. vignae. A host specificity test showed that the mung bean isolates of P. vignae were pathogenic toward mung bean with a much stronger virulence and toward adzuki bean with a relatively weak virulence, but they were nonpathogenic to the other tested legume crops, including soybean, cowpea, pea, common bean, faba bean, and chickpea. The host range of mung bean isolates significantly differs from those of P. vignae f. sp. adzukicola and P. vignae f. sp. vignae based on our results and on previous studies. Thus, the pathogen causing Phytophthora stem rot of mung bean is proposed as a new forma specialis of P. vignae, designated as P. vignae f. sp. mungcola.

Mung bean (Vigna radiate L.) is a major legume crop and widely planted in China. A new bacterial foliar disease similar to wildfire was observed on the mung bean plants. This study was conducted to determine the causal agent inducing wildfire-like symptoms on mung bean. The bacterial isolates obtained from mung bean were performed to detailed identification. All isolates showed the similar morphology and molecular characteristics to those of Pseudomonas syringae. By pathogenicity tests, the isolates were strongly pathogenic to mung bean and tobacco, a common host of wildfire disease. Based on the morphological and molecular characteristics, including the specific detection of toxin genes, rDNA sequences and a phylogenetic analysis, fatty acid composition, physiological and biochemical properties, all isolates were identified as P. syringae pv. tabaci. To the best of our knowledge, this is the first report of wildfire induced by P. syringae pv. tabaci on mung bean worldwide.

Southern corn rust (SCR), an airborne disease caused by Puccinia polysora, can severely reduce the yield of maize (Zea mays L.). Using recombinant inbred lines (RILs) derived from a cross between susceptible inbred line Ye478 and resistant Qi319 in combination with their high-density genetic map, we located five quantitative trait loci (QTLs) against SCR, designated as qSCR3.04, qSCR5.07, qSCR6.01, qSCR9.03, and qSCR10.01, on chromosomes 3, 5, 6, 9, and 10, respectively. Each QTL could explain 2.84 to 24.15% of the total phenotypic variation. qSCR6.01, detected on chromosome 6, with the highest effect value, accounting for 17.99, 23.47, and 24.15% of total phenotypic variation in two environments and best linear unbiased prediction, was a stably major resistance QTL. The common confidence interval for qSCR6.01 was 2.95 Mb based on the B73 RefGen_v3 sequence. The chromosome segment substitution lines (CSSLs) constructed with Qi319 as the donor parent and Ye478 as the recurrent parent were used to further verify qSCR6.01 resistance to SCR. The line CL183 harboring introgressed qSCR6.01 showed obvious resistance to SCR that was distinctly different from that of Ye478 (P = 0.0038). Further mapping of qSCR6.01 revealed that the resistance QTL was linked to insertion-deletion markers Y6q77 and Y6q79, with physical locations of 77.6 and 79.6 Mb, respectively, on chromosome 6. Different from previous major genes or QTLs against SCR on chromosome 10, qSCR6.01 was a newly identified major QTL resistance to SCR on chromosome 6 for the first time. Using RIL and CSSL populations in combination, the SCR-resistance QTL research can be dissected effectively, which provided important gene resource and genetic information for breeding resistant varieties.

Fusarium wilt is becoming an increasingly severe disease affecting mung bean in China. However, the pathogen has not thoroughly been identified. We therefore carried out a multi-year disease investigation and gathered an extensive collection of diseased mung bean plants, aiming to confirm the causal agent through morphological characterization, pathogenicity tests, molecular detection, and phylogenetic analysis. Field surveys were conducted for five consecutive years, covering the main mung bean-growing areas and spanning seven provinces of China. In total, 170 isolates with Fusarium oxysporum-like colonies were isolated from the collected samples, which were subsequently confirmed as F. oxysporum by morphological observation and PCR-based molecular detection. Then, 70 isolates (10/province) were subjected to pathogenicity tests and molecular detection of pathogenicity-related secreted in xylem (SIX) genes. Sixty-eight of the 70 isolates were pathogenic to mung bean and were verified to carry the pathogenicity-related genes SIX6 and SIX11, while the remaining two nonpathogenic isolates did not contain any SIX genes. Additionally, in a host range test of seven representative pathogenic isolates (1/province) on eight other crops, only two isolates caused mild symptoms on one of two adzuki bean cultivars, and no visual symptoms were observed on chickpea, common bean, cowpea, pea, rice bean, soybean, or cotton, indicating the isolates were host-specific to mung bean. Finally, phylogenetic analysis using multiple genes, TEF1-ɑ, IGS, mtSSU, SIX6 and SIX11, revealed that the seven mung bean isolates formed a unique clade distinct from other formae speciales of F. oxysporum. Here, the F. oxysporum isolates causing mung bean wilt were confirmed as an independent forma specialis distinguished from those affecting other crops.

Maize (Zea mays L.) is the most widely grown crop in China, which was planted 41.28 million hectares in 2019 (http://data.stats.gov.cnw/easyquery.htm?cn=C01z 1B). Macroconidia produced on carnation leaf agar (CLA) were relatively slender, slightly curved and thick-walled, mostly 3 to 5 marked septa, with a curved and tapering apical cell and poorly developed foot cell, 46.9 ± 5.6 µm × 4.9 ± 0.2 µm (Fig. 1C). Microconidia formed abundantly and were generally oval on CLA, 8.2 ± 0.5 µm × 3.4± 0.1 µm (Fig. 1D). No chlamydospores were observed. Morphological characteristics of the isolates matched the description of Fusarium thapsinum (Leslie and Summerell 2006). To further get the phylogenetic evidence, TEF1-α (translation elongation factor), RPB1 (the largest subunit of RNA polymerase II) and RPB2 (the second largest subunit of RNA polymerase II) were amplified with primer pairs EF1/EF2 (O'Donnell et al. 1998), thapR1F (5'-TTTTCCTCACAAAGGAGCAAATCATG-3')/thapR1R (5'-GTTCACCCAAGATATGGTCGAAAGCC-3'), and thapR2F (5'-ACTCTTTCACATTTGCGCCGAAC-3')/thapR2R (5'-CGGAGCTTTCGTCCAGTGTGAC-3'), and sequenced, respectively. The BLAST search of the sequences of EF1-α, RPB1 and RPB2 shared 99.87% to 100% identity with those of F. thapsinum strains deposited in the GenBank (Supplementary Table 1). Sequences from two isolates (XCCG-3-B-1 and XCCG-3-A-1) were deposited in GenBank (Accession No. MT550014, MT997082 for EF-1α; MT550011, MT997087 for RPB1 and MT550008, MT997091 for RPB2). The phylogenetic relationships based on analysis of the partial sequences showed the representive isolates clustered together with F. thapsinum at 96% bootstrap values (Fig. 2). Combined with the results of morphological characteristics and phylogenetic analysis, the strain designated as Fusarium thapsinum. To complete Koch's postulates, the pathogenicity of the isolates was tested using the silking-stage plants in a greenhouse based on previously described method with modification (Zhang et al. 2016). An 8 mm in diameter wound hole was created at the second or third internode of the plant above the soil surface and injected with 0.5 ml of mycelia plug. The inoculated stalk exhibited internal dark brown necrotic regions and the brown area elongated obviously around the insertion at 14 dpi (days post inoculation). At 30 dpi, the stalks turned soft, hollow and even lodging of the plants for those severe ones, which are similar to those observed on naturally infected maize plants in the field (Fig. 1F). When the roots of the three-leaf-stage seedlings were inoculated with 1×106 macroconidia solution (Ye et al. 2013), the root rot and leaf wilting symptoms were observed (Fig. 1E). While the control plants that were inoculated with only sterile water showed no disease symptoms. The pathogen was re-isolated from the inoculated tissues and the identity was confirmed by the morphological characters. Fusarium thapsinum had been described as causal agent of maize stalk rot in Pakistan (Tahir et al. 2018). To our knowledge, this is the first report of F. thapsinum associated with maize stalk rot in China. The discovery will strengthen the theoretical foundation of maize stalk rot disease management.

An emerging soilborne disease resembling Phytophthora stem rot was observed on mung bean plants grown in Anhui, China. To identify the causal agent, diseased plants and soil samples from 13 fields were collected to isolate the pathogen. Twenty-two

Maize stalk rot has become one of the most important diseases in maize production in China. From 2017 to 2019, a survey was conducted to determine the population diversity of Fusarium species associated with maize diseases in 18 cities across Henan Province. Maize stalk rot with an incidence of more than 20% that caused yield losses up to 30% was observed on maize variety Zhengdan958, which was grown in two continuous maize fields in Zhumadian City, Henan Province. The stem tissues from the boundary between diseased and healthy pith were chopped into small pieces (3 × 8 mm), disinfected (70% ethanol for 1 min) and then placed onto potato dextrose agar (PDA) amended with L-(+)-Lactic-acid (1 g/L) and incubated at 25°C for 4 days. Colonies on PDA produced fluffy, light yellow aerial mycelium and purple to deep brick red pigment at 25°C (Fig 1A, 1B). On carnation leaf agar (CLA), macroconidia in orange sporodochia formed abundantly, but microconidia were absent. Macroconidia were short and thick-walled, had 3 to 5 septa, a poorly developed foot cell and rounded apical cell (Fig 1C). These characteristics matched the description of Fusarium culmorum (Leslie and Summerell 2006) and isolates DMA268-1-2 and HNZMD-12-7 were selected for further identity confirmation. Species identification was confirmed by partial sequences of three phylogenic loci (EF1-α, RPB1, and RPB2) using the primer pairs EF1/EF2, CULR1F/CULR1R, and CULR2F/CULR2R, respectively (O'Donnell et al., 1998). The consensus sequences from the two isolates were deposited in GenBank (MZ265416 and MZ265417 for TEF, respectively; MZ265412 and MZ265414 for RPB1, respectively; MZ265413 and MZ265415 for RPB2). BLASTn searches indicated that the nucleotide sequences of the three loci of the two isolates revealed 99% to 100% similarity to those of F. culmorum strains deposited in the GenBank, Fusarium-ID, and MLST databases (Supplementary Table 1~3). Pathogenicity test was conducted at the flowering-stage using Zhengdan958 and Xundan20 plants according to previously described method (Zhang et al., 2016; Cao et al., 2021; Zhang et al., 2021). The second or third internodes of thirty flowering plants were drilled to make a wound approximately 8 mm in diameter using an electric drill. Approximately 0.5 mL inoculum (125 mL colonized PDA homogenized with 75 mL sterilized distilled water) was injected into the wound and sealed with Vaseline and Parafilm to maintain moisture and avoid contamination. Sterile PDA slurry was used as a control. Thirty days after inoculation, the dark-brown, soft rot of pith tissues above and below the injection sites were observed, and some plants were severely rotten and lodged (Fig 1D, 1E). These symptoms were similar to those observed in the field. No symptoms were observed on control plants. The same pathogen was re-isolated from the inoculated stalk lesions but not from the control, thereby fulfilling Koch's postulates. To our knowledge, this is the first report of F. culmorum as the causal agent of stalk rot on maize plants in China. Also, this fungus has been reported to cause maize ear rot in China (Duan et al. 2016) and produce mycotoxins such as trichothecenes, nivalenol, and zearalenone that cause toxicosis in animals (Leslie and Summerell 2006). The occurrence of maize stalk rot and ear rot caused by F. culmorum should be monitored due to the potential risk for crop loss and mycotoxin contamination.

In a field survey from 2017 to 2019, Fusarium stalk rot symptoms including discolored, disintegrated stalk pith tissues and lodged plants were observed in maize hybrid lines Fuyu1611, Jidan66, and ...

Southern corn rust (SCR), an airborne disease caused by

During 2017 to 2019, a field survey for maize stalk rot was conducted in 21 counties (districts) across the Guangxi province of China. This disease caused yield losses ranging from 20% to 30%. Maize plants with stalk rot were collected during the late milk stage and pieces of diseased pith tissue were cultured as previously described (Shan et al. 2017). Fungal colonies and mycelia with morphological characteristics of Fusarium species were subcultured onto fresh potato dextrose agar (PDA) and carnation leaf agar (CLA) plates. Based on morphological characteristics and molecular detection by amplification of Fusarium genus-specific primers (Duan et al. 2016), 39 Fusarium isolates were identified. Among them, five isolates from Du'an, Pingguo, Debao, and Daxin had abundant, pale orange to yellow aerial mycelium with deep red pigments when grown on PDA (Fig. 1A; 1B). The average growth rate was 8.0 to 12.0 mm per day at 25°C in the dark. The fungi produced two types of spores on CLA. Microconidia were ovoid to clavate, generally 0- to 3-septate, and 4.6 to 9.4 μm in length (n = 30) (Fig. 1D); Macroconidia were slightly curved with an acute apical cell, mostly 3- to 4- septate, and 19.4 to 38.2 μm in length (n = 30) (Fig. 1C). No chlamydospores were observed. These five isolates were initially identified as Fusarium kyushuense based on morphological features. PCR was performed to amplify three phylogenetic genes (TEF1-α, RPB1, and RPB2) (O'Donnell et al. 1998) and species specific primers kyuR1F/kyuR1R (5-TTTTCCTCACCAAGGAGCAGATCATG-3/5-TCCAATGGACTGGGCAGCCAAAACACC-3), kyuR2F/kyuR2R (5-CAGATATACATTTGCCTCGACAC-3/5-TACTTGAGCACGGAGCTTG-3) were used to confirm species identity. The obtained sequences were deposited in GenBank under the accession numbers MT997084, MT997080, MT997081 (TEF1-α); MT550012, MT997085, MT997086 (RPB1); MT550009, MT997089, and MT997090 (RPB2), respectively. Using BLAST, sequences of TEF1-α, RPB1, and RPB2 of the isolates were 99.33% (MH582297.1) to 100% (MG282364.1) similar to those of F. kyushuense strains (Supplementary Table 1). Based on phylogenetic analysis with maximum likelihood methods using tools of the website of CIPRES (http://www.phylo.org), isolates GX27, GX167, and GX204 clustered with F. kyushuense with 100% bootstrap support (Fig. 2). The pathogenicity of the three isolates was tested using young seedlings and adult plants as previously described with modification (Ye et al. 2013; Zhang et al. 2016). The primary roots of three-leaf-old seedlings were inoculated by immersing the roots into a 1 × 106 macroconidia solution, incubating for 6 h at 25°C, and transferring to normal growth conditions (26°C, 16 h light/22°C, 8 h dark). The second or third internode above the soil surface of flowering stage plants grown in a greenhouse was bored with a Bosch electric drill to make a hole (ca. 8 mm in diameter) and inoculated with 0.5 mL of mycelia plug then sealed with petrolatum. The inoculum was created by homogenizing five plates of flourish hyphal mats (approximately 125 mL) with kitchen blender and adjusting to a final volume of 200 mL with sterilized ddH2O. No symptoms were observed in the seedlings or adult plants that were mock-inoculated with PDA plugs. Three days post-inoculation (dpi), roots of the infected seedling turned dark-brown and shrunk and the leaves wilted (Fig. 1E). Typical stalk rot symptoms observed in the inoculated plants were premature wilting of entire plant and hollow and weak stalks, leading to lodging; the longitudinal section of the internodes exhibited obvious dark brown necrosis and reddish discoloration at 14 dpi and 30 dpi, respectively (Fig. 1F). Fusarium kyushuense was re-isolated from the inoculated stalk lesions but not from the control. This is the first record of stalk rot caused by F. kyushuense on maize plants in China. However, F. kyushuense is known to cause maize ear rot in China (Wang et al. 2014) and can produce type A and type B trichothecene mycotoxins in kernels (Aoki and O'Donnell 1998). The occurrence of maize stalk rot and ear rot caused by F. kyushuense should be monitored in China due to the potential risk for crop loss and mycotoxin contamination.

An emerging bacterial disease with symptoms resembling those of halo blight is threatening mung bean production in China. This study was conducted to investigate the disease’s geographic distribution in China using consecutive multiyear field surveys and to confirm the causative agents’ identity. The surveys were conducted in 15 provinces covering seven geographic regions from 2009 to 2014. The survey results revealed that the emerging mung bean disease has rapidly spread and is prevalent in three of the main Chinese geographic regions, which contain more than 90% of the mung-bean-growing areas in China. To confirm the causal agent, diseased mung bean leaves were collected from the surveyed fields and used to isolate the pathogen. A bacterium was consistently isolated from all of the collected leaves. Based on the phenotypic characteristics, the physiological and biochemical properties, pathogenicity tests, and fatty acid composition, in combination with specific polymerase chain reactions and 16S-23S ribosomal DNA sequence analyses, the bacterium was identified as Pseudomonas syringae pv. phaseolicola. To our knowledge, this is the first report of P. syringae pv. phaseolicola causing halo blight on mung bean in China. The results indicate that P. syringae pv. phaseolicola is likely of epidemiological significance on mung bean in China.

Mung bean (Vigna radiata L.) is an important legume crop cultivated widely in China (Nair et al. 2013). In September 2018, a severe foliar disease occurred on some mung bean cultivars (Jilv0816, Baolv200810-1, Liaolv10L708-5, and Zhonglv5) in Shijiazhuang (38°03'N, 114°29'E), Hebei Province, China. Initially, lesions were circular to irregular, with dark brown margins and pale centers (Supplementary Fig.1). Later, tiny dark stroma with oval or irregular shape were observed on spots. The infected field was about 0.067 hectare with 50-70% disease incidence, but with no significant yield losses. Several leaves with necrotic spots were collected and cut into 2-3-mm pieces, surface sterilized with 2% NaClO for 2 min, rinsed three times in sterile distilled water, and incubated on potato dextrose agar (PDA) at 25oC in darkness for 7 days. Three of 10 obtained single spore isolates, QB1, QB2 and QB3, were used for further studies. Colonies had abundant white aerial mycelia and produced black sporodochia bearing masses of viscid spores on PDA after 7-10 days. Conidia were aseptate, hyaline, and cylindrical, with the size of 5.6-7.5 µm × 1.6-3.3 µm (n=50). Conidiophores branched repeatedly. These morphological characteristics resembled that of Paramyrothecium-like isolates (Lombard et al. 2016). Given that P. roridum, P. foliicola, and P. nigrum were all reported to cause leaf spot on leafy vegetables and ornamental crops, five loci (the internal transcribed spacer (ITS), translation elongation factor 1-alpha (tef1), β-tubulin (tub2), 28S rRNA (LSU) and calmodulin (cmdA)) were amplified and sequenced for molecular analysis (Mati et al. 2019). The resulting sequences were deposited in GenBank under accession numbers: MK335967, MT415351-MT415364. Among the five loci, ITS and LSU sequences showed 99-100% (584/590, 545/546 base pairs) similarity with P. foliicola type strain CBS113121 (NR_145074.1; KU846324.1) by BLASTn analysis, while the tef1, tub2, and cmdA sequences exhibited high identity (99%) (398/404 bp, 323-324/326 bp, 555-558/560 bp) with P. foliicola strain Bas4_m2 (MH939239.1; MH824739.1; MH807772.1) (Mati et al. 2019). Phylogenetic tree of the five concatenated loci showed that our isolates cluster with P. foliicola, although they show slight difference from other P. foliicola strains (Supplementary Fig.2). Based on morphology and molecular analysis, the pathogen was identified as P. foliicola. Pathogenicity tests of the three isolates were performed by spraying 2 ml of 1.0 × 106/ml spore suspension on each three-week-old seedlings of mung bean cultivar 'Jilv 7' (n=5 for each isolate), whereas the controls were inoculated with sterile water (n=3). All inoculations were incubated in a moist chamber at 25oC with a 12h light cycle. The experiment was repeated twice. After 7 to 10 days, symptoms with necrotic brown spots were observed on plants inoculated with P. foliicola, but not on controls. The pathogen was reisolated from randomly selected diseased leaves and identified as P. foliicola by morphology and DNA sequencing of tub2 and cmdA loci. No pathogens were isolated from controls. Although P. roridum has been reported to cause mung bean leaf spot in India (Singh and Shukla 1997; Singh and Narain 2008), to our knowledge, this is the first report of P. foliicola causing leaf spot on mung bean in China. This finding suggests a potential threat to mung bean production in China and further studies should focus on epidemiology and control of this disease.

Bean weevil Acanthoscelides obtectus Say is one of the most destructive pests of bean seeds. Using 10 microsatellite loci, we studied the genetic diversity and differentiation of 13 geographical populations. A total of 79 alleles were detected, with an average of 7.900 alleles per locus. The gene flow and genetic differentiation rate values at the 10 loci varied from 0.376 to 1.560 and 13.8–39.9%, with averages of 0.774% and 24.4%, respectively. Among the 13 populations, the effective number of alleles and observed heterozygosity ranged from 1.865 to 2.848 and 0.457 to 0.646, respectively. Shannon's information index ranged from 0.684 to 1.104. In all comparisons, the fixation index (FST) values ranged from 0.021 to 0.463, with a total FST value of 0.228 among the 13 populations, indicating a moderate level of genetic differentiation among these populations. Analysis of molecular variance revealed that the genetic variation within populations accounted for 67.7% of the total genetic variation. Using the unweighted pair group method with arithmetic mean cluster analysis, 13 populations were clustered into three distinct genetic groups. The pattern of the three concentrated groups from principal component analysis showed a similar result to cluster, although some individuals interpenetrated with one another.

Mung bean (Vigna radiata) is an important legume crop in China. An emerging mung bean disease with symptoms resembling southern blight was detected in China. This study was conducted to confirm and characterize the responsible pathogen through cultural and morphological characterization, and molecular detection using multiple specific primers and multiple-clone sequence analysis of the rDNA internal transcribed spacer (ITS) region and the translation elongation factor 1α (EF1α) and RNA polymerase II subunit 2 (RPB2) genes. All isolates obtained from mung bean were identified as Sclerotium rolfsii. Interestingly, we found that rDNA ITS, EF1α, and RPB2 sequences of all isolates consisted of two distinct types, which likely originated from different nuclei. Our findings indicated that S. rolfsii isolates were heterokaryotic and contain a heterozygous genome. Two trials of pathogenicity and host range revealed that all S. rolfsii isolates were not only strongly virulent to mung bean but also to several other important crops, indicating their potential threat to future agricultural production. To our knowledge, this is the first report of S. rolfsii causing southern blight on mung bean in China.

Maize (Zea mays L.) is one of the most important crops in China. Ear rot is a serious disease that often leads to a decline in maize yield and quality and is a hazard to human and livestock health owing to potential mycotoxin contamination of grain. The incidence of maize ear rot usually ranges from 20 to 40% at different fields, even reaching as high as 70% at certain plots in Chongqing and surrounding areas (Zhou et al. 2018). In August 2016, a survey to determine population composition and distribution of Fusarium spp. causing maize ear rot was conducted in 22 counties in Chongqing. Maize ears with white, pink, or salmon-colored mold were collected from fields for further analysis. Symptomatic kernels were soaked in 2% sodium hypochlorite solution for 3 min, rinsed with sterile water three times, placed on acidified potato dextrose agar (PDA), and incubated at 26 ± 1°C for 3 to 5 days. The newly grown-out fungal colonies displaying morphological characteristics of Fusarium spp. were transferred onto fresh PDA and Spezieller Nahrstoffarmer agar and purified by the single-spore isolation method (Yang et al. 2008). Fusarium spp. were identified based on morphological characteristics (Leslie and Summerell 2006) and sequence analysis of the translation elongation factor-1α (TEF-1α), β-tubulin, and mitochondrial small subunit (mtSSU) genes (Jiang et al. 2018). The predominant Fusarium spp. were Fusarium verticillioides, F. proliferatum, and F. meridionale, which were the main causal agents of maize ear rot in these areas. In addition, morphological characteristics of several isolates from Beibei, Jiangjin, Xiushan, Rongchang, Kaixian, and Wanzhou Districts were found to be identical to those of Fusarium fujikuroi Nirenberg, which grouped into the Gibberella fujikuroi species complex. Colonies on PDA produced abundant white aerial mycelia initially, but the mycelia became pale pinkish and dark violet with age. Microconidia were abundant and small in size (4.9 to 11.3 × 2.2 to 3.2 µm), colorless, oval to club shaped, and 0- to 1-septate. Macroconidia were slender, almost straight, sickle shaped, medium length, with three to five septa (17.1 to 39.2 × 2.6 to 3.3 µm). No chlamydospores were observed. Identity of the fungus was also confirmed by sequence comparison of the partial TEF-1α, β-tubulin, and mtSSU genes of two representative isolates. The resulting sequences of the TEF-1α, β-tubulin, and mtSSU genes showed 100, 100, and 99% sequence identity to those of F. fujikuroi (GenBank accession nos. MH263736.1, MH263737.1, and MF984420.1, respectively). DNA sequences of partial TEF-1α, β-tubulin, and mtSSU genes from two representative isolates (FCQD90 and FCQD97) were deposited in GenBank under accession numbers MK328875 and MK328876, MK385626 and MK385627, and MK385628 and MK385629, respectively. A pathogenicity test was performed on maize inbred lines B73 and Ye 107. Four days after silk emergence, 2 ml of conidial suspension (1 × 10⁶ conidia /ml) of each isolate was injected into each of 10 maize ears through the silk channel. Control plants were inoculated with sterile distilled water. The typical Fusarium ear rot symptom (white or white-pink mold) was observed on inoculated ears and the infected kernels. No symptom developed on the water-inoculated controls. F. fujikuroi was reisolated from the symptomatic ears but not from the control. F. fujikuroi was previously reported associated with seedling damping-off on soybean, stem wilt of Canna edulis, and root rot of Reineckia carnea (Jiang et al. 2018; Pedrozo et al. 2015; Sun et al. 2018). To our knowledge, this is the first report of F. fujikuroi causing maize ear rot in China, and this disease should be paid sufficient attention owing to a serious risk of mycotoxin contamination in maize.

Fusarium wilt, caused by Fusarium oxysporum f. sp. mungcola (Fom), is an increasingly serious disease of mungbean (Vigna radiata (L.) R.Wilczek) in China. Pathogenic variability has been observed among Fom isolates; however, there are no reports describing Fom races or pathotypes. Thus, this study was conducted with the aim of developing a set of pathotype differentials to reveal Fom pathotype diversity by assessing virulence variability of Fom isolates. First, 105 mungbean cultivars were screened against a standard virulent Fom isolate (F08). Eleven of the 105 cultivars were selected as candidate differentials of Fom according to resistance phenotype and genetic background. Second, the resistance of the 11 candidate differential cultivars was tested against 30 Fom isolates from different geographical origins in China. Highly significant differences were observed among isolate × cultivar interaction patterns, indicating that pathotype differentiation exists in Fom isolates. Based on the different reaction patterns combining with genetic background, seven of the 11 cultivars were selected to constitute a set of differential hosts of Fom pathotype, used to distinguish pathotypes of 84 Fom isolates from different geographical regions by evaluating the virulence reaction pattern. The results showed that the 84 Fom isolates were defined as 12 pathotypes. Finally, we tried to confirm whether the 12 Fom pathotypes could be distinguished by a PCR-based diagnostic method based on the two genes (SIX6 and SIX11) reported to be associated with Fom pathogenicity. However, the Fom pathotype could not be distinguished by variation of the PCR products or their resulting sequences of the two genes. This is the first study to develop a set of Fom pathotype differential hosts and identify 12 Fom pathotypes, which provides important information for resistance breeding and disease control.

Fusarium verticillioides, F. proliferatum, and F. meridionale were identified as the predominant fungi among 116 Fusarium isolates causing maize ear and kernel rot, a destructive disease in Chongqing areas, China. The toxigenic capability and genotype were determined by molecular amplification and toxin assay. The results showed that the key toxigenic gene FUM1 was detected in 47 F. verticillioides and 19 F. proliferatum isolates. Among these, F. verticillioides and F. proliferatum isolates mainly produced fumonisin B1, ranging from 3.17 to 1566.44, and 97.74 to 11,100.99 µg/g for each gram of dry hyphal weight, with the averages of 263.94 and 3632.88 µg/g, respectively, indicating the F. proliferatum isolates on average produced about an order of magnitude more fumonisins than F. verticillioides did in these areas, in vitro. Only NIV genotype was detected among 16 F. meridionale and three F. asiaticum isolates. Among these, 11 F. meridionale isolates produced NIV, varying from 17.40 to 2597.34 µg/g. ZEA and DON toxins were detected in 11 and 4 F. meridionale isolates, with the toxin production range of 8.35–78.57 and 3.38–33.41 µg/g, respectively. Three F. asiaticum isolates produced almost no mycotoxins, except that one isolate produced a small amount of DON. The findings provide us with insight into the risk of the main pathogenic Fusarium species and a guide for resistance breeding in these areas.

During late August and early September 2011, stem rot symptoms were observed on adzuki bean plants (Vigna angularis) growing in fields located in Beijing and Hebei Province, China, respectively. In this study, four isolates were obtained from infected stems of adzuki bean plants. Based on their morphology, and sequence and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analyses of the ribosomal DNA internal transcribed spacers (rDNA-ITS) region, the four isolates were identified as Rhizoctonia solani in anastomosis group (AG) 4 HGI. Pathogenicity tests showed that all isolates were strongly pathogenic to adzuki bean and resulted in serious wilt symptoms which was similar to observations in the fields. Additionally, the isolates infected several other crops and induced related rot on the roots and basal stems. To our knowledge, this is the first report of Rhizoctonia solani AG 4 HGI causing stem rot on adzuki bean.

A novel Phytophthora sojae resistance gene RpsHC18 was identified and finely mapped on soybean chromosome 3. Two NBS–LRR candidate genes were identified and two diagnostic markers of RpsHC18 were developed. Phytophthora root rot caused by Phytophthora sojae is a destructive disease of soybean. The most effective disease-control strategy is to deploy resistant cultivars carrying Phytophthora-resistant Rps genes. The soybean cultivar Huachun 18 has a broad and distinct resistance spectrum to 12 P. sojae isolates. Quantitative trait loci sequencing (QTL-seq), based on the whole-genome resequencing (WGRS) of two extreme resistant and susceptible phenotype bulks from an F2:3 population, was performed, and one 767-kb genomic region with ΔSNP-index ≥ 0.9 on chromosome 3 was identified as the RpsHC18 candidate region in Huachun 18. The candidate region was reduced to a 146-kb region by fine mapping. Nonsynonymous SNP and haplotype analyses were carried out in the 146-kb region among ten soybean genotypes using WGRS. Four specific nonsynonymous SNPs were identified in two nucleotide-binding sites–leucine-rich repeat (NBS–LRR) genes, RpsHC18-NBL1 and RpsHC18-NBL2, which were considered to be the candidate genes. Finally, one specific SNP marker in each candidate gene was successfully developed using a tetra-primer ARMS-PCR assay, and the two markers were verified to be specific for RpsHC18 and to effectively distinguish other known Rps genes. In this study, we applied an integrated genomic-based strategy combining WGRS with traditional genetic mapping to identify RpsHC18 candidate genes and develop diagnostic markers. These results suggest that next-generation sequencing is a precise, rapid and cost-effective way to identify candidate genes and develop diagnostic markers, and it can accelerate Rps gene cloning and marker-assisted selection for breeding of P. sojae-resistant soybean cultivars.