First Report of Leaf Spot Caused by Corynespora cassiicola on Kiwifruit (Actinidia chinensis) in China

Evaluation of the control efficacy of antagonistic bacteria from V-Ti magnetite mine tailings on kiwifruit brown spots in pot and field experiments

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.

Occurrence Regionalization of Kiwifruit Brown Spot in Sichuan

Kiwifruit brown spot caused by Corynespora cassiicola is the most significant fungal disease in Sichuan, resulting in premature defoliation, which had a significant impact on yield and fruit quality. The objective of the study was to determine the occurrence regularity and suitability of kiwifruit brown spot in Sichuan. The occurrence of the disease in the main producing region was continuously monitored, the maximum entropy (MaxEnt) model was used to predict its potential distribution, and the key environmental variables were identified using the jackknife method. The results indicated that kiwifruit brown spot was widely distributed across the entire producing region in Sichuan, predominantly affecting the variety "Hongyang". The incidence (p < 0.01) and disease index (p < 0.05) showed a significant positive correlation with the cultivar, and decreased with the altitude increasing. The average area under the ROC curve (AUC) of 10 replicates was 0.933 ± 0.012, with an accuracy of 84.44% in a field test, confirming the reliability of the predicted results. The highly suitable distribution areas of kiwifruit brown spot were mainly located in the Chengdu and Ya'an regions. The entire Panzhihua region was an unsuitable distribution area, and the entire Pujiang County and Mingshan District were highly suitable distribution areas. The key environmental variables affecting the potential distribution of kiwifruit brown spot included isothermality (24.3-33.7%), minimum temperature in August (16.3-23.6 °C), maximum temperature in July (25.5-31.2 °C), minimum temperature in June (15.6-20.9 °C), precipitation in August (158-430 mm), and average temperature in October (15.6-18.8 °C). This study provides a theoretical basis for the reasonable layout of the cultivar and the precise prevention and control of the disease.

Co-Application of Tetramycin and Chitosan in Controlling Leaf Spot Disease of Kiwifruit and Enhancing Its Resistance, Photosynthesis, Quality and Amino Acids

Leaf spot disease caused by Lasiodiplodia theobromae and Alternaria tenuissima is a seriously fungal disease in kiwifruit production. In this study, the co-application of tetramycin and chitosan against leaf spot disease in kiwifruit and its effects on the disease resistance, photosynthesis, quality and amino acids of kiwifruit were investigated. The results show that tetramycin exhibited an excellent antifungal activity against L. theobromae and A. tenuissima with EC50 values of 2.37 and 0.16 mg kg−1. In the field, the foliar co-application of tetramycin and chitosan could effectively control leaf spot disease with control efficacy of 89.44% by spraying 0.3% tetramycin aqueous solutions (AS) 5000 time liquid + chitosan 100 time liquid, which was significantly (ANOVA, p < 0.01) higher than 79.80% of 0.3% tetramycin AS 5000 time liquid and 56.61% of chitosan 100 time liquid. Simultaneously, the co-application of tetramycin and chitosan was more effective than tetramycin or chitosan alone in enhancing the disease resistance and photosynthesis of kiwifruit leaves, as well as improving the quality and amino acids of kiwifruit fruits. This work highlights that chitosan is a practicable, cost-effective and eco-friendly adjuvant of tetramycin for controlling leaf spot disease of kiwifruit, enhancing resistance and photosynthesis of leaves and improving quality and amino acids of fruits.

Characterization and Pathogenicity of Pythium-Like Species Associated with Root and Collar Rot of Kiwifruit in Turkey

During the period of June to October in 2018, a widespread decline was observed on kiwifruit vines in the vineyards located in the Altınordu, Fatsa, and Perşembe districts of Ordu province in Turkey. The symptoms were associated with reddish-brown rots expanding from the root to the collar with sparse off-color foliage. Based on the percentage of the total infected samples across 18 vineyards, the most common oomycete species were Globisporangium intermedium (37.1%), Phytopythium vexans (34.3%), Globisporangium sylvaticum (14.3%), Globisporangium heterothallicum (11.4%), and Pythium dissotocum (2.9%). The morphological identification of isolates was confirmed based on partial DNA sequences containing the nuclear rDNA internal transcribed spacer region gene and the mitochondrial cytochrome c oxidase subunit II gene. The optimum growth temperature and the optimum pH values of the five species ranged from 22.98 to 28.25°C and 5.67 to 8.51, respectively. Pathogenicity tests on the seedlings of kiwifruit cv. Hayward revealed significant differences in virulence among isolates. Phytopythium vexans and Globisporangium sylvaticum isolates caused severe root and collar rot resulting in seedling death, while Globisporangium heterothallicum and Globisporangium intermedium isolates had relatively lower virulence. All Globisporangium spp. and Phytopythium vexans isolates significantly decreased plant growth parameters (plant height, shoot and root dry weights, and root length); however, Pythium dissotocum caused very mild symptoms and did not affect these parameters of growth. To our knowledge, this is the first study reporting Globisporangium sylvaticum, Globisporangium heterothallicum, and Globisporangium intermedium causing root and collar rot on kiwifruit not only in Turkey but also in the world.

Fine genetic mapping of target leaf spot resistance gene cca-3 in cucumber, Cucumis sativus L

The cucumber target leaf spot resistance gene cca - 3 was fine mapped in a 79-kb region harboring a CC-NB-ARC type R gene that may be responsible for the hypersensitive responses to infection of the target leaf spot pathogen in cucumber. The target leaf spot (TLS) is one of the most important foliar diseases in cucumber (Cucumis sativus L.). In this study, we conducted fine genetic mapping of a simply inherited recessive resistance gene, cca-3 against TLS with 193 F2:3 families and 890 F2 plants derived from the resistant cucumber inbred line D31 and the susceptible line D5. Initial mapping with microsatellite markers and bulked segregant analysis placed cca-3 in a 2.5-Mbp region of cucumber chromosome 6. The D5 and D31 lines were re-sequenced at 10× genome coverage to explore new markers in the target region. Genetic mapping in the large F2 population delimited the cca-3 locus in a 79-kb region with flanking markers Indel16874230 and Indel16953846. Additional fine mapping and gene annotation in this region revealed that a CC-NB-ARC type resistance gene analog, Csa6M375730, seems to be the candidate gene for cca-3. One single nucleotide polymorphism (SNP) was found in the NB-ARC domain of this candidate gene sequence between D31 and D5 that may lead to amino acid change, thus altering the function of the conserved NB-ARC motif. This SNP was validated in the segregating population as well as 24 independent cucumber lines. There was significantly higher level of cca-3 expression in the leaves of D5 (susceptible) than in D31 (resistant), and the expression level was positively correlated with the areas of necrotic spots on leaves after inoculation. It seems the cca-3 resistance gene was able to induce hypersensitive responses to the infection by TLS pathogen.