Abstract

Unripe avocado fruit in Mexico are affected by Colletotrichum spp. Although the literature indicates that unripe fruit are resistant to the fungus because of presence of compounds in the fruit, there is evidence on the intervention of pectate lyase (PL) as a virulent factor in Colletotrichum gloeosporioides. The objective of this work was to detect PL from the fungus in response to avocado cell wall under two pH conditions, to simulate infection in unripe (low pH) and ripe (high pH) fruit. Colletotrichum isolates were grown in a second liquid media at either pH 4 or 7. Enzyme activity was measured in the clear supernatant and PL was detected by immunoblot with an antibody against C. gloeosporioides PL, which detects a single PL. Results show that, in vitro, the fungus responds with higher enzyme activity when in contact with avocado cell wall at pH 7, than at pH 4. However, two of the isolates examined produced PL at pH 4. This behavior under acid conditions may be related to their pathogenicity in unripe fruit. To our knowledge, this is the first documentation of PL secretion by C. gloeosporioides at low pH and may help explain its ability to attack young avocado fruit.

Key words: Anthracnose, metabolites, pectinases, Persea americana.