Effects of wounding, inoculum density, and biological control agents on postharvest brown rot of stone fruits

The effects of wounding, inoculum density, and three isolates (New, Ta291, and 23-E-6) of Trichoderma spp, and one isolate (BI-54) of Rhodotorula sp. on postharvest brown rot of stone fruits were determined at 20 degrees C and 95% relative humidity (RH). Brown rot was observed frequently on wounded nectarine, peach, and plum fruits inoculated with two spores of Monilinia fructicola per wound, and occasionally on unwounded nectarine and peach fruits inoculated with the same spore load. Brown rot was observed on wounded plums only. A substantial increase in lesion diameter of brown rot was also recorded on wounded nectarines and peaches inoculated with suspensions of less than or equal to 20 spores and less than or equal to 200 spores per wound, respectively, compared with unwounded fruit. At concentrations of 10(7) and 10(8) spores per ml, all Trichoderma isolates substantially reduced brown rot on peaches (63 to 98%) and plums (67 to 100%) when fruits were inoculated with M. fructicola following the application of a biological control agent. Similarly, at 10(8) spores per ml, the yeast BI-54 also suppressed brown rot on peaches completely and on plums by 54%. Significant brown rot reduction was also achieved with the isolate New at a concentration of 10(8) spores per mi, even when the biocontrol agent was applied 12 h after inoculation with M. fructicola and under continuous conditions of 95% RH. The isolates Ta291 and 23-E-6 also reduced brown rot significantly under drier (50% RH) incubation conditions. These isolates provided the best control of brown rot on plums when they were applied 12 h earlier than inoculation with M. fructicola. Satisfactory control of brown rot on plums inoculated with M. fructicika at 8 x 10(4) spores per ml was achieved with New at 10(6) spores per mi and with Ta291 at 10(7) spores per mi. Measures taken to avoid injuring fruit will greatly reduce brown rot of stone; fruit at any spore load for plum, but only at less than or equal to 50 spores per mm(2) for peach, and at less than or equal to 5 spares per mm2 for nectarine. This study identifies two isolates (Ta291 and New) of Trichoderma atroviride, one isolate (23-E-6) of I: viride, and one of Rhodotorula sp. that show potential for further development as biocontrol agents of postharvest brown rot of stone fruits.