Biology of B. cinerea
In fruits and grapes flower infections followed by latency are having a big impact onto the epidemiology of grey mould. Several flower to fruit infection pathways can be seperated. In grapes, kiwifruits, raspberries infections trough the stylus into the ovule have been postulated. In the ovulus the pathogen stay latent, which seems to be a result of preformated host defence strategie (similar to the resveratrol content of young grape berry). In grapes, kiwifruits and strawberries infections trough the stamen, petals or septals have been found important. In grapes studies showed that B. cinerea could infect the stamens and grows basipetaly to infect the receptacle and then grows systemically to the pedicel and vascular tissues in the berries.
A 6 year research project in the Cape area showed that grape berries can be infected throug the stoma and lenticells of the pedicel and at a lower extend of the racheis. Pedicel infections are possible during flowering period too. Later this tissue increases resistance agianst B. cinerea infections.
Other infection pathways postulating the saprophytic growth of the pathogen on floral debris and the later infection of berries when the suscpetibility increases with ripening or by insect or hail damage of the berries. Assumption of conidia accumulation within the fruit during summer and the infection of susceptible berries later in the season is another thesis. Condidial infection of ripening fuits is possible from any inoculum source. Most probably a low number of latent infected berries are formed, which show extensive sporulation when suscpetibility of the berries increase with maturity. With can assume berries to become susceptible starting from a sugar content of 6%.
In kiwi fruit we have a big impact of picking conditions to the occurence of B. cinerea. Fruits picked with a wet surface can get infected by B. cinerea at the micro lessions set by the fingers of the pickers.
In practical control of B. cinerea we have to seperate two important infection periods: Flowering and senescence. During flowering we have susceptible young fruits, where the infection is followed by a latency period. While infection on matures (senescent) fruits will lead to symptoms without latency period. The importance of the infection during flowering in grapes can change form season to season and between region. In fruits where we have to expect some shelf live ( talbe grapes, kiwis or strawberries) the symptoms are seen when stored under cooled conditions in shops or storages. A chemical control of vine grapes showing a good resistance to B. cinerea during the flowering will not show any economic results. Therefore all conditions of risk and propability of infection, the susceptibility of the fruit and the shelf life, storage conditions have to be taken into consideration in the decision of an application agains Botrytis cinerea during flowering.
In stone fruits infection by B. cinerea occurrs mostly during flowering. At this time treatments against Monilina spp. are taken into considerations which also infect the Botrytis cinerea infection.