The fungal pathogen Corynespora cassiicola : A review and insights for target spot management on cotton and Soya bean

Ma D., Jiang J., Zhu J., Zhang L., Li B., Mu W., Liu F.

Necrotic lesions on leaves caused by Corynespora leaf spot (CLS) seriously threaten the quality and yield of cucumber in China. Corynespora cassiicola has developed different degrees of sensitivity to various fungicides due to its long-term and extensive application. In our work, the effect of isopyrazam and mefentrifluconazole on different life stages of C. cassiicola was examined. To determine the optimal effect of binary mixtures of isopyrazam and mefentrifluconazole, the two fungicides were mixed at different proportions. Furthermore, the disease suppression of isopyrazam, mefentrifluconazole, and their compound mixture against CLS was evaluated in greenhouse experiments. Ultraviolet (UV) mutagenesis and fungicide-selection methods were performed to assess the risk of resistance development. Among the three life stages tested, isopyrazam showed the weakest inhibition on mycelial growth, and mefentrifluconazole showed the strongest inhibition of germ tube elongation. According to Wadley’s and cotoxicity coefficient methods, the optimal proportion of the two-component mixture of isopyrazam and mefentrifluconazole was 1:1. Isopyrazam, mefentrifluconazole, and their binary mixture at 1:1 reduced the disease severity of CLS on potted cucumber plants, with protective effects of 31.11, 24.65, and 42.12% and curative effect of 33.90, 37.48, and 42.84%, respectively. Compared with isopyrazam or mefentrifluconazole alone, the binary mixture of the two fungicides at 1:1 did not exert significant influence on the change of C. cassiicola sensitivity. Undoubtedly, such data will greatly facilitate the screening of new fungicides for CLS and resistance management.

Li T., Xiu Q., Zhang J., Wang J.X., Duan Y.B., Zhou M.G.

Cucumber target spot, caused by Corynespora cassiicola, is a devastating fungal disease in greenhouses in China. Lack of resistant cultivars and unscientific use of fungicides aggravated the difficulty to manage this disease. In recent years, resistance of C. cassiicola to benzimidazoles, quinone outside inhibitors, and succinate dehydrogenase inhibitors has occurred in China. Here, we tested the fluazinam sensitivity distribution of 79 C. cassiicola isolates from different provinces in China based on mycelial growth inhibition. The EC50 values of fluazinam ranged from 0.1002 to 0.3129 µg/ml with a mean of 0.2136 ± 0.0495 µg/ml, and the sensitivity frequency was normally distributed (P = 0.2083, Shapiro–Wilk test). Meanwhile, the EC50 values for spore germination inhibition ranged from 0.0992 to 0.2278 µg/ml with a mean of 0.1499 ± 0.0504 µg/ml. This indicated that fluazinam exhibited an excellent in vitro fungicidal activity on both mycelial growth and spore germination. In addition, fluazinam also exhibited a good in planta control efficacy on detached cucumber leaves in the protective and curative assays. Moreover, the biological and physiological characteristics of C. cassiicola as affected by fluazinam were determined. Fluazinam not only significantly inhibited respiration and adenosine triphosphate production but also caused the increase of cell membrane permeability and the dysfunctions of cellular homeostasis. Interestingly, we found that fluazinam especially damaged vacuole structures, causing the redistribution of vacuole substances. Taken together, our findings provide not only essential references for resistance management of C. cassiicola but also interesting insights for further revealing the action mode of fluazinam against plant pathogens.

Hieu N.D., Nghia N.A., Uyen N.T., Chau N.N., Quoc N.B.

A total of 76 Corynespora cassiicola isolates collected from 16 rubber clones in several geographic regions of Vietnam, were studied for genetic diversity by ribosomal DNA internal transcribed spacer (rDNA-ITS) sequences and sequence-related amplified polymorphism (SRAP) techniques. Results of rDNA-ITS sequence analysis indicated 2 nucleotide polymorphisms at the 135th (cytosine/thymine) and 474th (guanine/adenine) base pair positions of rDNA-ITS region, which differentiated the 76 studied isolates into 3 clusters. All isolates could be uniquely distinguished by 208 polymorphism bands which generated 93.3% polymorphic ratio with SRAP markers. A dendrogram produced from UPGMA analysis based on Nei and Li’s coefficient divided the 76 C. cassiicola isolates into 2 main clusters. Cluster one included 54 fungal isolates of which 51 and 3 were observed in subgroup 1A and 1B, respectively. There were 22 C. cassiicola isolates belonging to cluster 2 with subgroups 2A and 2B consisted of 20 and 2 fungal isolates, respectively. Bootstrap values for groups one and two were 61% and 100%, respectively and the grouping was reliable, with similarity coefficient between the two main groups at 67%. rDNA-ITS sequence analysis revealed a new genetic group, signifying at least three C. cassiicola genetic groups that infect rubber trees in Vietnam. SRAP markers divided the studied isolates into two distinct groups, which correlated with geographical location rather than host source. To the best of our knowledge, this is the first demonstration using SRAP markers on the systematics of C. cassiicola isolates which cause the Corynespora leaf fall disease on various rubber (Hevea brasiliensis) clones in Vietnam.

Ortega-Acosta S.Á., Mora-Aguilera J.A., Velasco-Cruz C., Ochoa-Martínez D.L., Leyva-Mir S.G., Hernández-Morales J.

Roselle (Hibiscus sabdariffa L.) leaf and calyx spot induced by Corynespora cassiicola is one of the most important diseases that limit production, processing, and commercial use of this crop. The temporal progress of this disease was followed in four production locations in Guerrero, Mexico, during the 2014 and 2015 cycles. Disease incidence and severity were evaluated every 10 days through the 173-day production cycles. Epidemics were evaluated using the area under disease progress curves (AUDPCs) and Weibull model parameters. The highest severity and epidemic rate in calyces and leaves was registered in San Miguel, while the lowest was recorded in Xalpatlahuac in both cycles. Disease incidence in calyces was lower in Xalpatlahuac during both evaluation cycles and in leaves only in the 2015 cycle. The Weibull model properly described the epidemics (r = 0.93–0.99). The highest periods of epidemic growth in leaves were registered during flowering, development of calyces and foliar senescence; and in calyces during their physiological maturation and harvest. Severity on leaves and calyces was correlated with temperature from 20 to 30 °C (r = 0.80–1.0) and relative humidity higher than 90% (r = 0.80–1.0) (p < 0.05). The calyces severity was related to the leaves severity (r = 0.90–0.97) (p < 0.01).

Zhu J., Zhang L., Li T., Ma D., Gao Y., Mu W., Liu F.

Triazole fungicides with broad spectra constitute the standard strategy for the management of fungal diseases of cucumber. In this study, the in vitro activities of metconazole were tested based on mycelial growth using 121 Corynespora cassiicola isolates. The distribution of EC50 values of metconazole for 121 isolates was a unimodal curve with a mean of 0.78 ± 0.41 μg mL−1. Cross-sensitivity data indicated that sensitivity to metconazole did not correlate with sensitivity to difenoconazole, tebuconazole, myclobutanil or hexaconazole (P > 0.05). The relative treatment effect values shown by in vivo assays with detached cucumber leaves and potted seedlings indicated that the protective and curative effects of metconazole were higher than those of difenoconazole. Field data suggested that the application of metconazole at 150 g a.i. ha−1 markedly reduced the disease severity and disease incidence of Corynespora leaf spot compared with the effects obtained with difenoconazole treatment, with relative treatment effects of 0.24 and 0.17 for 2017 and 2018, respectively. These findings demonstrate that metconazole could play a vital role in the integrated management of cucumber Corynespora leaf spot.

MacKenzie K.J., Xavier K.V., Wen A., Timilsina S., Adkison H.M., Dufault N.S., Vallad G.E.

Target spot of tomato caused by Corynespora cassiicola is one of the most economically destructive diseases of tomato in Florida. A collection of 123 isolates from eight counties in Florida were evaluated for sensitivity to azoxystrobin and fenamidone based on mycelial growth inhibition (MGI), spore germination (SG), detached leaflet assays (DLAs), and sequence-based analysis of the cytochrome b gene (cytb). Cleavage of cytb by restriction enzyme (Fnu4HI) revealed the presence of a mutation conferring a glycine (G) to alanine (A) mutation at amino acid position 143 (G143A) in approximately 90% of the population, correlating with quinone outside inhibitor (QoI) resistance based on MGI (<40% at 5 μg/ml), SG (<50% at 1 and 10 μg/ml), and DLA (<10% severity reduction). The mutation conferring a phenylalanine (F) to leucine (L) substitution at position 129 (F129L) was confirmed in moderately resistant isolates (#9, #19, and #74) based on MGI (40 to 50% at 5 μg/ml), SG (<50% at 1 μg/ml and >50% at 10 μg/ml), and DLA (>10% and <43% severity reduction) for both QoI fungicides, whereas sensitive isolates (#1, #4, #7, #28, #29, #46, #61, #74, #75, #76, #91, #95, and #118) based on MGI (>50% at 5 μg/ml), SG (>50% at 1 μg/ml and 10 μg/ml), and DLA (>50% severity reduction) correlated to non-mutation-containing isolates or those with a silent mutation. This study indicates that QoI resistance among C. cassiicola isolates from tomato is widespread in Florida and validates rapid screening methods using MGI or molecular assays to identify resistant isolates in future studies.

Ul Haq I., Sarwar M.K., Faraz A., Latif M.Z.

Direct protection using synthetic chemicals is one of the basic principles of plant disease management. Historical perspectives of using chemicals for plant diseases control Include application of effective methods for controlling plant diseases. Fungicides, Bactericides and Nematicides are applied through different methods such foliar, slurry, drench, paste etc.). Fungicides or Fungistatics, can be classified based on mode of action, usage and composition. Limitations of pesticide usage occur in plant disease management, due to health hazards and pesticide impact on the environment. Insurgence of fungicidal resistance in plant pathogens is also a significant threat. Efficacy of chemicals compounds is also affected by climate changes. Recent trends in the development and use of synthetic chemicals (broad spectrum and new chemistry fungicides) in plant disease control Consider a comparison between pesticides and alternative plant disease control methods, fungicide marketing policies and procedures.

Dutta S., Kamei A., Goldar S., Datta G., Bharati D.R., Ghorai A.K., Pathak S., Roy Barman A., Jash S., Ray S.K.

Among the various biotic and abiotic factors limiting production of tomato, target leaf spot disease caused by Corynespora cassiicola has been emerged as a serious problem in vegetable based croppi...

Roth M.G., Webster R.W., Mueller D.S., Chilvers M.I., Faske T.R., Mathew F.M., Bradley C.A., Damicone J.P., Kabbage M., Smith D.L.

AbstractSoybean (Glycine max L.) is a major crop grown in the United States but is susceptible to many diseases that cause significant yield losses each year. Consistent threats exist across both northern and southern production regions and include the soybean cyst nematode, charcoal rot, and seedling diseases. In contrast, significant soybean diseases like Phytophthora stem and root rot, sudden death syndrome, and Sclerotinia stem rot (white mold) are intermittent threats that can be heavily influenced by environmental factors. Additional threats to soybean production that have emerged in recent years as more common problems in soybean production include root-knot and reniform nematodes, frogeye leaf spot, and Diaporthe diseases. Disease in any crop will only occur when the three components of the disease triangle are present: a susceptible host, a virulent pathogen, and a conducive environment. If an environment is becoming more conducive for a particular disease, it is important that farmers and practitioners are prepared to manage the problem. The information in this review was compiled to help assist agriculturalists in being proactive in managing new soybean diseases that may be emerging in new areas. To do this, we provide: 1) an overview of the impact and disease cycle for major soybean diseases currently causing significant yield losses in the United States, 2) a comprehensive review of the current management strategies for each soybean disease, and 3) insights into the epidemiology of each pathogen, including the likelihood of outbreaks and expansion to additional geographic regions based on current trends in climate change.

Banguela-Castillo A., Ramos-González P.L., Peña-Marey M., Godoy C.V., Harakava R.

Reznikov S., De Lisi V., Claps P., González V., Devani M.R., Castagnaro A.P., Ploper L.D.

Diseases are among the main factors that reduce soybean yields in Tucumán and other provinces in northwestern Argentina. The main diseases that affect the foliage of soybean plants in this region are target spot (caused by Corynespora cassiicola ), Cercospora leaf blight ( Cercospora kikuchii ), and Asian soybean rust ( Phakopsora pachyrhizi ). The objective of this work was to evaluate the efficacy and application timing of different chemical fungicides for the management of these diseases in northwestern Argentina. Field trials were conducted during three growing seasons (2014/2015, 2015/2016, and 2016/2017). The fungicide treatments that presented statistical differences ( P < 0.05) for target spot control compared to the untreated control in all growing seasons were those that included pyraclostrobin + epoxiconazole + fluxapyroxad (applied at R3, R5 and R3 + R5) and pyraclostrobin + epoxiconazole and azoxystrobin + cyproconazole at R3. For Cercospora leaf blight control, all treatments differed statistically from the untreated control in the 2014/2015 crop season, except for azoxystrobin + cyproconazole and azoxystrobin + benzovindiflupyr applied at R3 and pyraclostrobin + epoxiconazole at R5. Only azoxystrobin + cyproconazole at R3 in 2015/2016 and all the fungicide treatments in 2016/2017 differed statistically from the untreated controls. Soybean rust severity at R6 was low, 1.0% and 3.0% in the untreated control during 2014/2015 and 2015/2016, respectively, but increased to 54.2% in 2016/2017. Treatments that showed the lowest soybean rust severity values in the latter season were pyraclostrobin + epoxiconazole + fluxapyroxad (R3 + R5 and R5, with 17.4 and 17.1%, respectively), and azoxystrobin + benzovindiflupyr (R3 and R5, with 20.2 and 15.0%, respectively). Overall in this season, the efficacy of each fungicide for ASR control was better when applied at R5 than at R3. The treatments pyraclostrobin + epoxiconazole + fluxapyroxad applied at R3, R5 and R3+ R5 and treatments azoxystrobin + benzovindiflupyr and pyraclostrobin + epoxiconazole at R5 yielded significantly higher than the untreated control during all three seasons. These results should help improve management of soybean foliar diseases in northwestern Argentina. • Target spot, Cercospora leaf blight, and soybean rust are important soybean diseases. • We evaluated efficacy and application timing of fungicides for their control. • For each disease we determined the best fungicide treatment and moment of application. • Results obtained will improve soybean disease management in northwestern Argentina.

Wu J., Xie X., Shi Y., Chai A., Wang Q., Li B.

Corynespora cassiicola is an important plant pathogen with a wide host range. We investigated pathogenic and genetic variation among 69 C. cassiicola isolates from 16 hosts in China. Based on the i...

Rondon M.N., Lawrence K.S.

Corynespora cassiicola C.T. Wei is a widespread plant pathogenic fungus that causes target-shaped necrotic spots on plant leaves and on stems, roots, flowers, and fruits and has been recorded worldwide on up to 400 plant species. The disease is known as Corynespora leaf spot or target spot on cotton and soybean. A single DNA fragment (600 bp) was amplified using described primers, and based on cytb nucleotide sequences, four out of 12 isolates of C. cassiicola were found to have a mutation that replaces the codon for amino acid 143 from GGT to GCT, resulting in an amino acid change from glycine to alanine (G143A). All four isolates were sampled from soybean plants located in north (LIM14) and central (ELM04, ELM06, and ELM07) Alabama. No other point mutation on cytb was found for six C. cassiicola isolates sampled on cotton (BRW03, MAC01, FHP01, FHP22, HSV01, and HSV12) or on other two isolates sampled on soybean (LIM02 and LIM13). Other known mutations were found in our isolates. According to the Fungicide Resistance Action Committee, C. cassiicola rapidly developed resistance to fungicides and is an example of a pathogen that must be classified as a high risk of developing resistance to a different fungicide class. To the best of our knowledge, the present study is the first to report a G143A mutant in C. cassiicola from field populations in the United States.

Zhu F., Shi Y., Xie X., Chai A., Li B.

Corynespora blight, caused by Corynespora cassiicola (Berk. & M.A. Curtis) C.T. Wei, has become an important disease affecting cucumber in China. Its management mainly depends on fungicides; however, no research has been conducted to assess the sensitivity of C. cassiicola in China to boscalid, a succinate dehydrogenase inhibitor (SDHI). To facilitate boscalid resistance monitoring, baseline sensitivity was established. The EC50 value (i.e., the concentration that results in 50% mycelial growth inhibition) frequency distribution was unimodal with a right-hand tail; with the means 0.95 ± 0.51 μg/ml and the range 0.03 to 2.85 μg/ml. We then assessed the sensitivity of C. cassiicola to boscalid using discriminatory doses and EC50 values. In total, 27.8% of the 798 isolates were resistant, distributed in five provinces and two municipalities. Thirty-seven isolates with different resistance levels to boscalid were also evaluated for their sensitivity to carboxin, fluopyram, and penthiopyrad. Seven SDHI resistance patterns were observed (i.e., I: BosMRFluoMRPenLRCarSS; II: BosVHRFluoSSPenMRCarR; III: BosLRFluoMRPenLRCarR; IV: BosMRFluoMRPenMRCarR; V: BosHRFluoMRPenHRCarR; VI: BosHRFluoHRPenHRCarR; and VII: BosHRFluoSSPenLR CarR, VHR: very highly resistant; HR: highly resistant; MR: moderately resistant; LR: low resistant; R: resistant; SS: supersensitive), corresponding to seven mutations in sdhB/C/D genes, respectively.

Duan Y., Xin W., Lu F., Li T., Li M., Wu J., Wang J., Zhou M.

Target leaf spot caused by Corynespora cassiicola is an economically important foliar disease on cucumber. In recent years, this disease has caused a serious problem on greenhouse-cultivated cucumber in China. In this study, to explore the characteristics and possible causes of heavy occurrence of the disease, we monitored the resistance of C. cassiicola strains from different provinces of China to benzimidazole and quinone outside inhibitor (QoI) fungicides. The results from sequence comparison of target genes β-tubulin and Cytb of 619C. cassiicola strains indicate that resistance frequency to benzimidazoles and QoIs is up to 100%. Furtherly, molecular resistance mechanism of C. cassiicola to benzimidazoles and QoIs was analysed. One single mutation E198A and three double mutations E198A&M163I, E198A&F167Y and E198A&F200S were observed in target gene β-tubulin, which confers resistance to benzimidazoles. To our knowledge, this is the first report that double mutations of β-tubulin confer resistance to benzimidazoles in filamentous fungi. Compared with single mutation E198A, three double mutations significantly decreased sensitivity to benzimidazoles. Moreover, significant difference of sensitivity to benzimidazoles was observed among three double mutations. These mutation genotypes of β-tubulin have different geographical distribution and the mutation E198A&M163I is prevalent, occupying for 63.94%. In addition, strong cross resistance patterns between carbendazim, benomyl and thiabendazole were observed in C. cassiicola strains conferring different β-tubulin mutations. For QoI resistance, the only mutation G143A of Cytb was detected in tested 619C. cassiicola strains. Strong positive cross resistance was observed when comparing the EC50 values of sensitive and resistant strains of C. cassiicola for six intrinsically different QoIs such as azoxystrobin, fluoxastrobin, pyraclostrobin, fenaminstrobin, picoxystrobin and coumoxystrobin. Taken together, all the results not only provide novel insights into understanding resistance mechanism to benzimidazoles and QoIs in filamentous fungi, but also provide some important references for resistance management of target leaf spot on cucumber.

Peng Q., Hao X., Liu C., Li X., Lu X., Liu X.

Matanog A.K., Solpot T.C., Bretaña B.L., Tanabe M.E., Cabasan M.T.

Jayawardena R.S., Hyde K.D., Aumentado H.D., Abeywickarama P.D., Avasthi S., Dissanayake A.J., Gautam A.K., Gajanayake A.J., Armand A., Balendres M.A., Calabon M.S., Chen Y.J., Chethana K.W., Ferdinandez H.S., Gomdola D., et. al.

Luca G.D., Fattori Jr I.M., Marin F.R.

Mo Y., Bier R., Li X., Daniels M., Smith A., Yu L., Kan J.

Agricultural practices affect soil microbes which are critical to soil health and sustainable agriculture. To understand prokaryotic and fungal assembly under agricultural practices, we use machine learning-based methods. We show that fertility source is the most pronounced factor for microbial assembly especially for fungi, and its effect decreases with soil depths. Fertility source also shapes microbial co-occurrence patterns revealed by machine learning, leading to fungi-dominated modules sensitive to fertility down to 30 cm depth. Tillage affects soil microbiomes at 0-20 cm depth, enhancing dispersal and stochastic processes but potentially jeopardizing microbial interactions. Cover crop effects are less pronounced and lack depth-dependent patterns. Machine learning reveals that the impact of agricultural practices on microbial communities is multifaceted and highlights the role of fertility source over the soil depth. Machine learning overcomes the linear limitations of traditional methods and offers enhanced insights into the mechanisms underlying microbial assembly and distributions in agriculture soils. Machine learning breaks through the linear limitations of traditional methods, providing deeper insights into the assembly, interactions, and mechanisms underlying microbiomes at varying soil depths under different farming practices.

Lopes I.S., Soares J.K., de Medeiros L.S., Coronato Courrol L.

Phytopathogenic fungi significantly threaten global food security, causing substantial yield and quality losses. Sustainable solutions are urgently needed to combat these agricultural pathogens. This study explored the potential of silver (Ag), copper (Cu), and combined Ag/Cu nanoparticles capped with aminolevulinic acid (ALA) as antifungal agents. The nanoparticles (ALAAg, ALACu, and ALAAgCu) were synthesized via photoreduction and characterized using various techniques (UV-Vis, TEM, XRD, Zeta potential). Their antifungal activity against four key plant pathogens (Alternaria grandis, Colletotrichum truncatum, Corynespora cassiicola, and Fusarium oxysporum) was evaluated using poisoned food techniques. Notably, ALAAgCuNPs demonstrated superior antifungal activity compared to a conventional fungicide against two fungal strains. Even at lower concentrations, ALAAgCuNPs exhibited fungistatic effects comparable to those of the control. These promising results suggest the potential of ALAAgCu NPs as a broad-spectrum, potentially eco-friendly alternative for fungal control in plants and seeds. This approach is crucial for ensuring crop health, harvest quality, and food safety.

Kruthika R., Khan F., Karan R., Ashwini K.S., Chandana R., Ramesh G.V., Bevanur A., Chethan D., Poonacha T.T., Palanna K.B.

Babchi (Psoralea corylifolia) is an anciently known medicinal plant commonly found in sub-tropical and temperate parts of India and China. In January 2023, typical target spot symptoms were observed on the leaves of babchi plants in ornamental gardens at GKVK, Bangalore, India. The distinctive spots were extensively present on the foliage viz., leaves, petiole and stem but prominently in older leaves. Pathogenic isolation, purification and morphological characterisation revealed the associated pathogen belongs to the genus Corynespora. Multilocus sequencing and phylogenetic analysis of internal transcribed spacer (ITS) region, actin (ACT) and calmodulin (Cal) regions confirmed Corynespora cassiicola as the causal organism responsible for target leafspot in babchi. Further, pathogenicity was established by proving Koch's postulates. To the best of our knowledge, this is the first report of C. cassiicola causing target leaf spot on babchi plant in India.

King K.M., Canning G.G., West J.S.

To date, there have been no DNA-based metabarcoding studies into airborne fungi in tropical Sub-Saharan Africa. In this initial study, 10 air samples were collected onto Vaseline-coated acrylic rods mounted on drones flown at heights of 15–50 meters above ground for 10–15 min at three sites in Ghana. Purified DNA was extracted from air samples, the internal transcribed spacer (ITS) region was amplified using fungal-specific primers, and MinION third-generation amplicon sequencing was undertaken with downstream bioinformatics analyses utilizing GAIA cloud-based software (at genus taxonomic level). Principal coordinate analyses based on Bray–Curtis beta diversity dissimilarity values found no clear evidence for the structuring of fungal air communities, nor were there significant differences in alpha diversity, based on geographic location (east vs. central Ghana), underlying vegetation type (cocoa vs. non-cocoa), or height above ground level (15–23 m vs. 25–50 m), and despite the short flight times (10–15 min), ~90 operational taxonomic units (OTUs) were identified in each sample. In Ghanaian air, fungal assemblages were skewed at the phylum taxonomic level towards the ascomycetes (53.7%) as opposed to basidiomycetes (24.6%); at the class level, the Dothideomycetes were predominant (29.8%) followed by the Agaricomycetes (21.8%). The most common fungal genus in Ghanaian air was cosmopolitan and globally ubiquitous Cladosporium (9.9% of reads). Interestingly, many fungal genera containing economically important phytopathogens of tropical crops were also identified in Ghanaian air, including Corynespora, Fusarium, and Lasiodiplodia. Consequently, a novel loop-mediated isothermal amplification (LAMP) assay, based on translation elongation factor-1α sequences, was developed and tested for rapid, sensitive, and specific detection of the fungal phytopathogenic genus Lasiodiplodia. Potential applications for improved tropical disease management are considered.

Cui Y., Zhu Y., Dong G., Li Y., Xu J., Cheng Z., Li L., Gong G., Yu X.

Seemingly barren heavy-metal-polluted vanadium (V) and titanium (Ti) magnetite mine tailings contain various functional microbes, yet it is unclear whether this includes microbial resources relevant to the biological control of plant diseases. Kiwifruit brown leaf spot disease, caused by Corynespora cassiicola, can seriously reduce kiwifruit yield. To discover effective control measures for kiwifruit leaf spot, 18 bacteria strains among 136 tailing-isolated bacteria from V-Ti magnetite mine tailings were identified as inhibiting C. cassiicola by the confrontation plate method, indicating that antagonistic bacteria surviving in the V-Ti magnetite mine tailings were present at a low level. The 18 antagonistic strains could be divided into two BOX-A1R clusters. The 13 representative strains that were selected for phylogenetic tree construction based on their 16S rRNA sequences belonged to the Bacillus genus. Five predominant strains exhibited different toxin-production times and intensities, with four of them initiating toxin production at 32 h. Among them, Bacillus sp. KT-10 displayed the highest bacteriostatic rate (100%), with a 37.5% growth inhibition rate and an antagonistic band of 3.2 cm against C. cassiicola. Bacillus sp. KT10 also showed a significant inhibitory effect against the expansion speed of kiwifruit brown spots in the pot. The relative control effect was 78.48 and 83.89% at 7 days after the first and last spraying of KT-10 dilution, respectively, confirming a good effect of KT-10 on kiwifruit brown leaf spots in the field. This study demonstrated for the first time that there are some antagonistic bacteria to pathogenic C. cassiicola in V-Ti magnetite mine tailings, and Bacillus sp. KT10 was found to have a good control effect on kiwifruit brown leaf spots in pots and fields, which provided an effective biological control measurement for kiwifruit brown leaf spots.

Mo Y., Bier R., Li X., Daniels M., Smith A., Yu L., Kan J.

Abstract Background: Soil microbiomes are critical to soil health and sustainable agriculture. Microbiome structures differ across agricultural soils that experience different management practices, such as tillage, fertilizers, and cover crops. Environmental factors, including those related to soil management, and microbiome-interactions alter these microbial communities. However, the full extent of these influences and relationships is not comprehensively understood. Here, we applied machine learning-based methods to identify prokaryotic and fungal assembly and distribution across various soil depths from fields under different agricultural practices. Results: Fertility source was the most pronounced agricultural factor for microbial assembly, especially for fungal communities, and this impact lessened as soil depth increased. Furthermore, fertility source shaped co-occurrence patterns within the microbial community, leading to fertility source-sensitive modules dominated by fungi down to 30 cm soil depth. Tillage predominantly affected microbial communities in soil depths of 0-20 cm, and not only enhanced microorganism dispersal but also amplified stochastic processes, especially in the prokaryotic community. However, tillage potentially jeopardized interactions within the microbiome. In contrast to the fertility source and tillage, cover crops had a less pronounced effect on microbial communities, with no clear depth-dependent patterns; however, they still affect microbial co-occurrence patterns to some extent. Additionally, microorganisms at varying depths, specifically 0-20 cm for tillage and cover crops and 0-60 cm for fertility sources, were indicative of different agricultural practices. Conclusions: Our result showed that the impact of agricultural practices on microbial communities is multifaceted, including the assembly process, interactions, and recruitment of specific microorganisms. We also demonstrated that machine learning models can overcome certain limitations of traditional methods, offering enhanced insights into the mechanisms underlying microbial assembly and distribution in agriculture soils.

Peng Q., Li X., Li G., Hao X., Liu X.

The cucumber target spot, caused by Corynespora cassiicola, is a major cucumber disease in China. Mefentrifluconazole, a new triazole fungicide, exhibits remarkable efficacy in controlling cucumber target spot. However, the resistance risk and mechanism remain unclear. In this study, the inhibitory activity of mefentrifluconazole against 101 C. cassiicola isolates was determined, and the results indicated that the EC50 values ranged between 0.15 and 12.85 μg/mL, with a mean of 4.76 μg/mL. Fourteen mefentrifluconazole-resistant mutants of C. cassiicola were generated from six parental isolates in the laboratory through fungicide adaptation or UV irradiation. The resistance was relatively stable after ten consecutive transfers on a fungicide-free medium. No cross-resistance was observed between mefentrifluconazole and pyraclostrobin, fluopyram, prochloraz, mancozeb, or difenoconazole. Investigations into the biological characteristics of the resistant mutants revealed that six resistant mutants exhibited an enhanced compound fitness index (CFI) compared to the parental isolates, while others displayed a reduced or comparable CFI. The overexpression of CcCYP51A and CcCYP51B was detected in the resistant mutants, regardless of the presence or absence of mefentrifluconazole. Additionally, a two-way mixture of mefentrifluconazole and prochloraz at a concentration of 7:3 demonstrated superior control efficacy against the cucumber target spot, achieving a protection rate of 80%. In conclusion, this study suggests that the risk of C. cassiicola developing resistance to mefentrifluconazole is medium, and the overexpression of CcCYP51A and CcCYP51B might be associated with mefentrifluconazole resistance in C. cassiicola. The mefentrifluconazole and prochloraz two-way mixture presented promising control efficacy against the cucumber target spot.

Delgado da Rocha V., Carolina da Silva Dal'Sasso T., Dal-Bianco Lamas Costa M., Orlando de Oliveira L.

Once deposited in the plant cell wall, pectin undergoes demethylesterification by endogenous pectin methylesterases (PMEs), which play various roles in growth and development, including defense against pathogen attacks. Pathogen PMEs can alter pectin's methylesterification pattern, increasing its susceptibility to degradation by other fungal pectinases and thus playing a critical role as virulence factors during early infection stages. To investigate the evolutionary history of PMEs in the Dothideomycetes class of fungi, we obtained genomic data from 15 orders (79 species) and added genomic data from 61 isolates of Corynespora cassiicola. Our analyses involved maximum likelihood phylogenies, gene genealogies, and selection analyses. Additionally, we measured PME gene expression levels of C. cassiicola using soybean as a host through RT-qPCR assays. We recovered 145 putative effector PMEs and 57 putative non-effector PMEs from across the Dothideomycetes. The PME gene family exhibits a small size (up to 5 members per genome) and comprises three major clades. The evolutionary patterns of the PME1 and PME2 clades were largely shaped by duplications and recurring gene retention events, while biased gene loss characterized the small-sized PME3 clade. The presence of five members in the PME gene family of C. cassiicola suggests that the family may play a key role in the evolutionary success of C. cassiicola as a polyphagous plant pathogen. The haplogroups Cc_PME1.1 and Cc_PME1.2 exhibited an accelerated rate of evolution, whereas Cc_PME2.1, Cc_PME2.2, and Cc_PME2.3 seem to be under strong purifying selective constraints. All five PME genes were expressed during infection of soybean leaves, with the highest levels during from six to eight days post-inoculation. The highest relative expression level was measured for CC_29_g7533, a member of the Cc_PME2.3 clade, while the remaining four genes had relatively lower levels of expression.

Sierra-Orozco E., Sandoya G., Lee S., Vallad G., Hutton S.

Corynespora cassiicola (Cc) is a genetically diverse ascomycete found worldwide in tropical and subtropical regions. Cc causes necrotrophic diseases in several plant species, including important crops such as rubber tree, tomato, cotton, and cucumber. Evidence suggests the involvement of one or more Cc host-specific toxins in disease progression. Management of Cc crop diseases is based mainly on pesticide sprays. However, the pathogen’s development of resistance to commonly used fungicides is documented. Resistance breeding is an attractive alternative or supplement to chemical control of Cc crop diseases, but research on this topic is very limited. This review describes the current plant resistance breeding efforts towards Cc resistance and discusses the potential influence of host-specific toxins (HSTs) on such efforts. Although some reports of host resistance exist in a few crops, resistant germplasm and knowledge about resistance mechanisms are limited. Some studies have suggested the involvement of HSTs in disease development, including the upregulation of resistance-related proteins in susceptible reactions and the recessive nature of resistance. In light of this, host resistance may not be achieved through commonly used dominant R-genes.

Zhang S., Sun Q., Cao Y., Ji Y., Zhang Y., Herrera-Balandrano D.D., Chen X., Shi X., Wang S., Laborda c P.

Corynespora cassiicola is a hazardous fungal pathogen that causes target spot disease in soybean. Numerous resistant C. cassiicola strains have emerged during recent years, leading to uncontrolled spreads and enormous economic losses in several soybean production areas. For these reasons, new methods for the control of this pathogen are urgently needed. In this study, a new Meyerozyma caribbica strain, NJC41, was isolated from C. cassiicola-infected soybean plants in China and identified by ITS and LSU sequencing. NJC41 inhibited C. cassiicola mycelial growth, and showed high colonization ability in soybean pods, maintaining its population for one week. NJC41 produced antifungal phenethyl alcohol, which was detected at 44.6 μg/mL in NJC41 secretions, and competed for space and nutrients with C. cassiicola. Curative application of 1 × 109 cells/mL NJC41 reduced C. cassiicola symptoms by 47.1%, providing higher curative efficacy than commercial fungicide carbendazim (29.8% lesion length inhibition). This study reveals the first biocontrol method for the management of target spot disease in soybean.

de Castro Costa É., Dias-Neto J.J., Bizerra L.V., Tormen N., Paul P.A., Café-Filho A.C.

Brazilian soybean is mainly grown in the Cerrado, the South American Savannah. We report epidemiological studies of soybean target spot (STS), caused by Corynespora cassiicola in two Cerrado regions in the Federal District (DF) and the state of Bahia (BA), relating the environmental parameters with disease intensities. Here we: i) characterize the field response of soybean cultivars to STS and compute their respective latent periods; ii) relate STS severity to yield; and iii) verify the cross-reaction of C. cassiicola isolates of soybean and cotton to each of these hosts. Ten commercial soybean cultivars were cultivated in DF and BA fields. Additionally, the cv. reactions were studied in greenhouse assays in the spring/summer and autumn/winter seasons. Precipitation and relative humidity were higher in DF than in BA, whereas the temperature was cooler with fewer extremely hot days. Greater STS intensity was observed in DF, reaching 48% incidence and 19% severity. Fungicide applications reduced disease only in the DF trial. Cultivars were separated into four groups: highly susceptible, susceptible, moderately resistant, and resistant. Higher disease severities were recorded in the spring/summer than in the autumn/winter. Length of latent periods correlated with the cv. response to STS and climate conditions. Environmental differences were the probable causes for the lower disease levels recorded in the BA fields and in the autumn/winter trial. A negative relationship was established between severity and yield. In the cross-inoculation studies, isolates of soybean and cotton were able to infect both hosts, but aggressiveness correlated with the host of origin.