Epidemiology of brown rot (Monilinia fructigena) on apple: infection of fruits by conidia

Effects of fruit maturity, wound age, temperature and the duration of wetne ss periods on infection of apple fruits by conidia of the brown rot fungus, Monilinia fructigena, were studied. Inoculation of fruits on potted apple trees and harvested mature fruits showed that wounding was essential for in fection by M. fructigena. On potted trees, there was a significant differen ce between the susceptibility of cvs Cox and Gala and this difference depen ded on wound age. The incidence of brown rot was affected greatly by fruit maturity and wound age. Wounds on younger fruits were more resistant to inf ection than those on older fruits, whilst the older the wound, the more res istant it was to infection. Furthermore, the degree of wound age-related re sistance was greater on younger fruits than on older fruits. These relation ships were well described by regression models. The effect of the duration of wetness periods was very small: increasing the duration of wetness perio ds reduced the incidence of brown rot on older wounds. For detached fruits, all those wounded were rotted after inoculation, except for those in two t reatments under 20 degrees C on fruits with wounds which were 8 days old. T he incubation period of the fungus was generally very short. Wound age was the single most important factor influencing the length of the incubation p eriod; the incubation period increased as wound age increased.