Search

Leaf mould caused by Fulvia fulva is a major disease of tomato in Japan. Resistance to several types of fungicides, including succinate dehydrogenase inhibitors (SDHIs), has been reported in isolates from Japan. In this study, we evaluated the sensitivity of F. fulva to SDHI fungicides, SDHI fungicide efficacy in controlling sensitive and resistant isolates, and the presence of mutations in the Sdh B gene, the target site of SDHI fungicides. The minimum inhibitory concentration (MIC) of six SDHI fungicides, excluding isofetamid, ranged from 0.1 to >100 μg/mL against mycelial growth of 45 F. fulva isolates collected in Nara prefecture, Japan, whereas that of isofetamid ranged from 0.1 to only 10 μg/mL. The peak MIC distribution of fluopyram and isofetamid was 10 μg/mL, that of inpyrfluxam was 100 μg/mL and was >100 μg/mL for the remaining SDHI fungicides. In a greenhouse inoculation experiment, only isofetamid controlled the highly resistant isolates with an MIC of 10 μg/mL and the remaining fungicides had MIC >100 μg/mL. In addition, moderately and highly resistant isolates were controlled by the application of isofetamid 6 h or 7 days before inoculation or 3 days after inoculation. Mutations in the Sdh B gene were not observed among sensitive, moderately resistant and highly resistant isolates, suggesting that mutations in other Sdh genes and/or changes in efflux pump expression were involved. Our results indicate the presence of cross‐resistance and different levels of sensitivity reduction among SDHI fungicides. Isofetamid showed the lowest resistance development among the tested SDHI fungicides and is considered effective in controlling tomato leaf mould. [ABSTRACT FROM AUTHOR]

This study has been proved that statistical experimental designs offer efficient and feasible approaches for determination of culture medium and fermentation conditions of Streptomyces lavendulae Xjy. Nutrition and cultural conditions have high influence on the antibiotic production of S. lavendulae Xjy. Soya bean meal, NaCl and ( NH4)2 SO4 were identified as the best ingredients for high antifungal activity of Xjy based on single variable experiments. Using response surface methodology, the best concentrations of medium ingredients were 1.46% soya bean meal, 2.25% NaCl and 1.26% ( NH4)2 SO4. The potential components were reduced from seven to three, and the antibiotic activity was increased by 10%. The optimized conditions for Xjy in a 250-ml Erlenmeyer flask were initial pH 5, medium volume 25 ml/250 ml and inoculation volume 10% at 30°C with 200 rpm by response surface methodology. Validation experiments carried out to check the accuracy of the models indicated that the predicted values agreed with the experimental values. The extension of necrosis lesion of Botryosphaeria dothidea was impeded by the application of Xjy in apple fruit. In tomato plants, Xjy showed the 43.7-51.7% curative and protective effects against Fulvia fulva. The optimal medium not only gave a 20% increase in antifungal activity, but it provided a simpler formulation. The results will set a basis for further study on large-scale fermentation volumes using S. lavendulae Xjy and be useful for the development of more advanced control strategies on plant diseases. [ABSTRACT FROM AUTHOR]

A procedure for producing high yields and high regeneration frequencies of protoplasts from Fulvia fulva is described. This procedure was devised by systematic trials of various parameters, such as culture age and osmotic support, which are known to affect protoplast yield and regeneration. Mycelium from liquid cultures of 24-48 h, incubated with Novozym 234 in buffered 1.0 M MgSO4, gave the best conditions for protoplast release. Regeneration frequencies up to 50% were obtained with a complete medium containing 0.8 M sucrose for osmotic support. [ABSTRACT FROM AUTHOR]