Efficacy of biocontrol yeasts combined with calcium silicate or sulphur for controlling durum wheat powdery mildew and increasing grain yield components

Powdery mildew, caused by Blumeria graminis f. sp. tritici, has been recognized as the main and widespread disease of wheat in the growing areas of this crop. In the present study, to set up new effective and eco-compatible control methods against the pathogen, the activity of three biological control agents (BCAs), the yeasts Rhodosporidium kratochvilovae, strain UM350, and Cryptococcus laurentii, strain UM108, and the yeast-like fungus Aureobasidium pullulans, strain LS30, previously selected for their high activity against different pathogens on various crops, were tested for two consecutive years on durum wheat in the field. The BCAs were tested alone or in combination with two mineral salts (calcium silicate and calcium chloride) or with low doses of wettable sulphur or with synthetic fungicides (azoxystrobin, tebuconazole or tetraconazole) currently used for controlling this disease. Treatments were applied twice, at the flag leaf and at pre-flowering stages. Disease severity, total yeast population dynamic on wheat leaves, grain yield components (grain yield, grain number, grain weight) were recorded. In both years, the results of the investigations showed that (i) at the flag leaf phenological stage, disease severity on untreated wheat leaves was very high (up to 63%); (ii) the sprayed BCAs colonized wheat plant phylloplane at high rate; (iii) the BCAs, applied alone or in combination with the two mineral additives or with fungicides, compared with untreated control, in general not only reduced the disease severity (up to 89%), but also increased grain yield (up to 35.3%) and grain weight (up to 13.2%) of durum wheat. Among the integrated treatments, the highest level of disease reduction as well as better levels of grain yield components were supplied by BCAs combined with calcium silicate or sulphur. Collectively, our results demonstrated that integrated approaches based on the combination of biocontrol yeasts with suitable additives or low doses of fungicides have a high potential for large-scale applications in eco-compatible agriculture for both controlling wheat powdery mildew and improving grain yield components.