Assessment of pathogenicity and infection requirements of Monilinia species causing brown rot of stone fruit in Australian orchards

This study investigated the effect of wetness duration on blossom blight development and the effects of Monilinia species, wetness duration, temperature and wounding on brown rot development in detached fresh market stone fruit. Both Monilinia fructicola and M. laxa infected ripe peach (cv. Autumn snow), nectarine (cv. Arctic snow) and apricot (cv. Robada), but M. laxa caused lower incidence of infection and no infection on plums (cv. Su Plum 11). Short wetness durations (2, 4 or 6 h at 15 and 20 °C) were sufficient for infection of ripe peach, plum, apricot and nectarine by M. fructicola, but on young fruit (5 weeks after full bloom) only peach and nectarine were infected at similar wetness durations at 5, 10, 15, 20 and 25 °C. Infection of young nectarine and ripe apricot and plum fruit was influenced by the wetness duration, and infection of ripe apricot by temperature. Under longer wetness durations (12 and 24 h at 15 and 20 °C), the susceptibility of the four fruits to M. fructicola was affected by fruit maturity. Nectarine and peach were more susceptible when ripe than as young fruit and least susceptible at pit hardening. Plum and apricot were also more susceptible when ripe than as young fruit. Infection of wounded fruits by both Monilinia species was 100 % in the four fruits tested at both immature and mature stages. In controlled field inoculations, M. fructicola infected peach flowers after 3 h wetness duration at 24 °C and thereafter blossom blight incidence increased with longer wetness duration (5, 8 and 20 h) at temperatures ranging from 16 to 24 °C. The results will be used to improve prediction of brown rot infection risk in stone fruit production in Australia.