Effect of a Strobilurin-Class Fungicide on Water Use in Synthetic Bread Wheat Genotypes Grown under Increasing Water Deficit Conditions

Three synthetic bread wheat genotypes and their parental cultivar Cham 6 were used to examine the effects of a strobilurin-class fungicide pyraclostrobin on leaf temperature, root water uptake and grain yield under increasing water deficit conditions. Wheat plants of Cham 6 treated with the pyraclostrobin at the booting stage showed a rapidly increased leaf temperature as compared with the gradually increased leaf temperature of the untreated plants. The final temperature reached, however, was lower for the pyraclostrobin treated plants than the untreated. Potted soil of the treated wheat plants also showed higher water contents than the untreated potted soil, suggesting delay of plant water uptake by pyraclostrobin treatment. A variation in water uptake by roots was also found between the four wheat genotypes examined. Daily water uptake was depressed after the pyraclostrobin treatment in all four wheat genotypes. Grain yields were slightly increased by the pyraclostrobin treatment in field trials under controlled water supply whereas no significant differences were detected in soil water content between treatments. The increase in grain yield by pyraclostrobin treatment might be dependent on the different water uptake of the wheat genotypes. These results suggest that foliage treatment of pyraclostrobin fungicide on wheat delays root water uptake, resulting in postponement of soil dehydration, which contributes to a slight increase of grain yield in some wheat genotypes in the field under water deficit conditions.