Compatibility of Rhodotorula glutinis (Lv316) biopesticide with chemical fungicides used in blackberry crops

Abstract: Blackberry fruit production in Colombia is lower than national demand due to the impact of several diseases. The most limiting disease is gray mold caused by Botrytis cinerea, which causes yield losses higher than 72%, followed by anthracnose caused by Colletotrichum spp. and downy mildew caused by Peronospora sparsa. Chemical fungicides are the main method to control these pathogens but considering the current market trends to reduce chemical residues in food, a biopesticide formulated as a concentrated suspension and based on yeast Rhodotorula glutinis strain Lv316 isolated from blackberry phyllosphere was developed. This biopesticide reduced 75% gray mold incidence under controlled conditions, and 65% under field conditions, higher efficacy than obtained by difenoconazole and carbendazim application (45% and 26%, respectively). However, fungicides applied to control anthracnose and downy mildew might affect the yeast. The objective of this study was to determine the compatibility of the developed biopesticide with difenoconazole, carbendazim and cupric hydroxide used to control anthracnose and dimetomorf, mandipropamid and azoxystrobin used to control downy mildew. Chemical fungicides in different doses (100%, 75%, 50%, 25% and 5% of commercial recommended dose) were in vitro evaluated. Biopesticide was compatible with carbendazim, dimetomorf, mandipropamid and azoxystrobin in all evaluated doses and with cupric hydroxide at 5% of recommended dose, showing similar viability as control (biopesticide unexposed to fungicides) after 72 hours fermentation in YM liquid medium supplemented with the fungicides. The yeast did not growth in media supplemented with difenoconazole and cupric hydroxide from 25% to 100% of recommended dose and evidenced changes in cells morphology, which indicated incompatibility with these molecules. This study allowed concluding that the developed biopesticide and selected compatible fungicides are viable tools to be included in integrated management programs for a safety blackberry production.