Yield gain due to fungicide application in varieties of winter wheat (Triticum aestivum) resistant and susceptible to leaf rust

In three independent experiments in Turkey and Kazakhstan, winter wheat germplasm with variable degrees of resistance to leaf rust was subjected to fungicide protection. The yield loss of genotypes susceptible to leaf rust varied from 30% to 60% depending on the environment and severity of infection. Genotypes completely or moderately resistant to leaf rust also responded positively to fungicide protection, with average yield increases in the range 10–30%. This increase was observed even in one season without leaf rust infection. The main character affected by fungicide was 1000-kernel weight. There was stable expression of the magnitude of yield gain in resistant genotypes in different seasons, confirming genetic variation for this trait. Possible mechanisms of yield gain from fungicide protection in resistant genotypes are related to a positive physiological effect of the chemical used as well as a possible ‘cost of resistance’ to wheat plants. The magnitude of yield gain by resistant germplasm justifies its capture in breeding programs to develop varieties resistant to diseases and with greater benefits from the fungicide protection.