Role of the oxidative metabolism in induced resistance or susceptibility mechanism during the interaction of avocado with Phytophthora cinnamomi Rands.

ABSTRACT The disease caused by the oomycete Phytophthora cinnamomi Rands affects most avocado (Persea americana) varieties, requiring additional tools for the selection of resistant materials. In the present study, induction of defense responses related to the oxidative metabolism in avocado was evaluated as a support for establishing its role in the defense responses during infection by this oomycete. Infection trials were carried out with the avocado clones ‘Duke 7’ (tolerant) and ‘Hass’ (susceptible), which had their stem base inoculated with the pathogen and whole leaves sampled at 0, 3, 24, 48 and 120 hours after infection (hai), for subsequent evaluation of the activities of the enzymes superoxide dismutase (SOD) and ascorbate peroxidase (APX), as well as for assessment of free radical scavenging capacity, total polyphenol content and caspase 3-like activity. The area under the disease progress curve was 1.3 and 14.8 (cm.day-1) for ‘Duke 7’ and ‘Hass’, respectively, and the former showed high resistance to the oomycete, which correlated with higher APX activity, higher free radical scavenger activity, and expression of caspase 3-like activity. Resistance or susceptibility in avocado during interaction with Phytophthora cinnamomi is suggested to be mediated by the participation of induced and innate antioxidants and by the induction of apoptosis responses in the resistant genotype ‘Duke 7’, whereas there is lack of such responses in ‘Hass’, the susceptible genotype.