Postharvest biocontrol of Monilinia laxa, Monilinia fructicola and Monilinia fructigena on stone fruit by two Aureobasidium pullulans strains

The antagonistic effects of yeasts,L1 and L8, isolated from carposphere of ‘Redhaven’ peachesweretested for the first time in the same experiment against three Monilinia species (M. laxa, M.fructicola and M.fructigena)in in-vitro and in-vivo trials. The two antagonists were selected after preliminary assaysfor their ability to reduce brown rot in peaches and nectarines, and both were identified by molecular and morphological tools as Aureobasidiumpullulans.Inin-vivo trials, neither the autoclaved cells, nor the sterile culturefiltrates of eitherantagonist showed any significant reduction of rot incidence produced by inoculaofthe three Monilinia species, while the washed cells of L1 and L8 completely inhibited M. laxa and M. fructicola rots and reducedM. fructigena infections by 70%and 90%, respectively. In other trials, nectarines treated with antagonist cells and inoculated with the pathogens were stored at 0°C for 21 days, plus 7 days at 20°C. The low temperature reduced brown rot development, since all fruit were free from disease symptomson removal from cold storage. However after 7 d at 20°C, untreated fruit were rotted over 45% depending on theMonilinia speciesbut theantagonists completely inhibited M. laxa and M. fructicola, while M. fructigena infections were reduced by89.8% and 91.2% by L1 and L8, respectively. For both strains,108cfu ml-1 was the most active concentration, althoughL1 showed good activity at a concentration of 107CFU ml-1.IsolateL8 at the concentration of 107 CFU ml-1was ineffective againstM. fructicola and M. fructigena, showing no difference between treated fruit and the control,excepting the case of nectarines inoculated with M. laxa, where L8 at the concentration of107cfu ml-1reducedthe brown rot infections with respect to the control. The increase in population density of A. pullulans strains L1 and L8 in the wounds of nectarines stored at 0° or 20°C was low but sufficient to control brown rot. In conclusion, the present preliminary study identified two antagonistic strains of A. pullulans as active ingredients forthe development of biofungicidesfor postharvest application against three Monilinia species that are responsible forhigh economic losses in stonefruit crops.