Streptomyces sp. Found in Infected European Pears Provides Protection Against Penicillium expan-sum and Colletotrichum fioriniae in Pome Fruits

Multiple fruit rot diseases impact pome fruit yield and consumer safety, including blue mold, bitter rot, white rot, gray mold, and Alternaria fruit rot. The occurrence of fungicide resistance in these pathogens is a continual concern, and for some pathogens the number of effective fungicides is very limited. These issues necessitate continued research into novel disease mitigation strategies. Here, Streptomyces sp. isolate WV22015 was discovered and isolated from European pears and showed broad-range inhibitory activity in plate biocontrol assays, with reductions of 18.6%-61.7% in the fungal fruit rot pathogens Penicillium expansum, Botrytis cinerea, Botrytosphaeria dothidea, Colletotrichum fioriniae, C. siamense, Diaporthe eres, Fusarium sp., Alternaria sp., and the stone fruit pathogen Monilinia fructicola. In wounded fruit assays, WV22015 reduced lesion diameters of P. expansum by 9.0-21.4% after 7 days depending on treatment concentration in Bartlett pears, and 20.1% in Gala apples. Against C. fioriniae, WV22015 led to a 12.6-17.5% decrease in lesion size in Bartlett pears, and a 25.4-54.0% decrease after 7 days when WV22015 was added to wounds 5 days before pathogen inoculation. P. expansum growth was completely prevented by culture filtrates of WV22015 and reduced by 68.0% by autoclaved culture filtrate at 50%v/v in PDA after 3 days. Overall, we demonstrate the potential of Streptomyces sp. as a new biocontrol agent against fruit rots in pome fruit crops.