Monilia spp. on peach and nectarines
Symptoms of the brown rot disease are the blight of the blossom as well as the green tip of twigs due to the penetration of the pathogen into the open blossom through the stigma of pistils or anthers. This usually results in wilting of the whole part of an one-year-old twig. The leaves start to hang down, later they become brown and rigid, but usually do not fall down on the soil, they remain on the tree until the spring of the next year. Sometimes, especially under humid conditions droplets of gum are visible, which are symptoms of colonisation of the fungus as well as the established cankers.
Figure 1. Brown rot and fungal sporulation on peach fruit. (Courtesy D.F. Ritchie) Figure 2. Peach fruit mummies. Notice the tan fungal sporulation on the mummy in the right photo. (Courtesy D.F. Ritchie) http://www.apsnet.org/EDCENTER/K-12/TEACHERSGUIDE/BROWNROT/Pages/Background.aspx Brown rot, caused by Monilia spp. (Monilia laxa, Monilia fructigena and Monilia fructicola) belong to the most destructive diseases on stone fruits through Europe.
The infected fruits are covered by putrefactive spots, from which warty sporodochia (hyphe) with conidia of the "summer" form appear. Additionally, in late autumn and winter, the fungus produces sporodochia of the "winter" form on infected twigs. With time, severely affected fruits become mummified. The mycelium growing in such mummies gradually aggregates into sclerotia. Such fruits remain on the tree during winter.
Temperature and wetness duration are important environmental factors, determining the infection incidence of M. laxa on blossoms. Monilia laxa is well adapted to the relatively low temperatures during spring and cause infections at temperatures as low as 5°C within a very short period of wetness duration. The infection of the active bloom trough the stima does not need very much leaf wetness. Leaf wetness is only needed for germination of the conidia. Therefore infection of the young fruit needs longer leaf wetness periods. To infect the young fruit an appressoria has to be formed and free moisture is needed to build up the pressure to form the infection peg to enter the epidermis cell. With maturity of the fruit small scars on the fruits allow an infection without infection peg again and the needed leaf wetness duration becomes shorter again.
In FieldClimate the Infection as well as the severity of infection is calculated by the factors of rain, leaf wetness, rel. humidity and temperature.