Apple fruits and grapevine leaves were inoculated with four wild-type strains of Botrytis cinerea. Two types of symptoms were
observed on apple, firm or soft rot. Extracts from infected tissues were analysed for polygalacturonase (PG) and pectin
methylesterase (PME) isozyme profiles. They showed that different specific PG isozymes occur in grapevine leaves and in soft rot on
apple fruit. PG and PME profiles were also studied in genetic transformants altered in their colonization ability and/or the type of
rot that they caused on apple fruit. No PG activity was found in apples infected by firm-rotting wild-type strains or transformants,
whereas two neutral PG isozymes (pIs 7.3 and 7.6) were expressed in soft-rotting strains. No association was found between the
production of these PG isozymes and the colonization level. The PME patterns were not correlated with the rotting type nor the
colonization level. In vitro, firm-rotting strains and transformants showed no PG activity in glucose medium whereas soft-rotting
ones produced several PG isozymes. In polygalacturonic acid cultures, all strains and transformants produced a single, common acidic
isozyme. Unlike PG, no variation in the PME isozyme patterns in vitro could be correlated with the culture substrate on apple or the
rotting type. The variation in pectinase profiles between in vitro and in planta contexts and the role of PGs in B. cinerea
pathogenicity on apple fruit is discussed. We suggest that neutral PG isozymes are involved in the soft-rotting type on apple fruit.