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

Abstract

The antagonistic effects of yeasts, L1 and L8, isolated from carposphere of ‘Redhaven’ peaches were tested for the first time in the same experiment against three Monilinia species (Monilinia laxa, Monilinia fructicola and Monilinia fructigena) in in vitro and in vivo trials. The two antagonists were selected after preliminary assays for their ability to reduce brown rot in peaches and nectarines, and both were identified by molecular and morphological tools as Aureobasidium pullulans. In in vivo trials, neither the autoclaved cells, nor the sterile culture filtrates of either antagonist showed any significant reduction of rot incidence produced by inocula of the three Monilinia species, while the washed cells of L1 and L8 completely inhibited M. laxa and M.fructicola rots and reduced M. 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 21days, plus 7days at 20°C. The low temperature reduced brown rot development, since all fruit were free from disease symptoms on removal from cold storage. However after 7d at 20°C, untreated fruit were rotted over 45% depending on the Monilinia species but the antagonists completely inhibited M. laxa and M. fructicola, while M. fructigena infections were reduced by 89.8% and 91.2% by L1 and L8, respectively. For both strains, 10⁸CFUml⁻¹ was the most active concentration, although L1 showed good activity at a concentration of 10⁷CFUml⁻¹. Isolate L8 at the concentration of 10⁷CFUml⁻¹ was ineffective against M. 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 of 10⁷CFUml⁻¹ reduced the 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 for the development of biofungicides for postharvest application against three Monilinia species that are responsible for high economic losses in stone fruit crops.