Conditions for infection of strawberry fruit by M. piriformis and Rhizopus spp.

Botrytis cinerea, Mucor piriformis and Rhizopus spp. are mainly responsible for post-harvest fruit rot in strawberry in the UK. However, research to date has been focused on the epidemiology and management of B. cinerea in strawberry (i.e., grey mould). A number of experiments were carried out to study the epidemiology of M. piriformis and Rhizopus on strawberry, including flower/fruit susceptibility, inoculum dose, in vitro spore germination and infection of both detached and attached fruit. The results showed that M. piriformis and Rhizopus had very similar epidemiological characteristics. Both pathogens were unable to infect flowers, but fruit became increasingly susceptible from the green development stage onwards. In vitro germination required near-saturation humidity conditions and was reduced in both low and high temperatures. However, infection of attached ripe fruit and subsequent rot development were relatively unaffected by temperature and relative humidity conditions that commonly occur under field conditions in the UK. On detached ripe fruit, a high spore infection potency was observed for both pathogens. Infection of fruit was completed within 9 to 24 h. Thus, the most important factor determining the level of infection of fruit by M. piriformis and Rhizopus in UK commercial crops is probably the number of spores deposited on the fruit. Management strategies should be targeted at reducing inoculum concentrations within crops in order to minimise the risk of fruit infection by M. piriformis and Rhizopus.