Induction of resistance under different watering regimes

Abstract: Several chemical and biological inducers effectively induce resistance against the foliar plant disease powdery mildew (Podosphaera aphanis) in strawberry plants. We tested the effects of three different irrigation regimes on the performance of several materials known to induce systemic resistance. The inducers acibenzolar-S-methyl (BTH), Trichoderma harzianum T39 (Trichodex) and nutrient broth (NB) and isolates of the yeast Rhodotorula glutinis and the bacterium Pseudomonas fluorescens were applied to the root zones of strawberry plants as drenches. Strawberry powdery mildew was affected by the frequency of irrigation; the limited irrigation regime (once every 2 days) restricted the development of disease. All of the drench treatments induced resistance under all three irrigation regimes, but disease suppression was less pronounced when irrigation was less frequent (watering once a day or once every 2 days, as opposed to twice a day). The growth of the powdery mildew-infected plants was affected by the frequency of irrigation and was promoted by the inducers. In some cases, the growth-promotion effect of the inducer was nullified by the water shortage.