Abstract

ANDRADE-HOYOS, Petra et al. Defense mechanisms in avocado rootstocks to Phytophthora cinnamomi Rands. Rev. Mex. Cienc. Agríc [online]. 2015, vol.6, n.2, pp.347-360. ISSN 2007-0934.

The study of the resistance in plants to root diseases are often evaluated at a macroscopic level, that is, selecting plants with healthy appearance and surviving the inoculum pressure regardless of histological resistance mechanisms to root pathogens, as is the case of Phytophthora cinnamomi causing the "sadness of avocado." The aim of this study was to identify the presence of P. cinnamomi mycelium in the xylem of the root and the mechanisms involved in resistance-tolerance in avocado plants from five varieties of rootstocks. The studied mechanisms were tylose formation and phenolic deposits. The presence of hyphae in xylem, tylose formation and phenolic accumulation in roots from dead plants with wilt symptoms and asymptomatic of Duke-7 and Thomas, Tepetl, Atlixco and Tepeyanco rootstocks was noted which were previously inoculated with P. cinnamomi under controlled temperature on the soil (17 and 28 °C). Mycelium content in the xylem of dead plants Duke-7, Thomas and Tepetl to 17 °C showed no significant differences; however, at 28 °C the mycelium content in Duke-7 was highly significant (p< 0.05). In wilted plants, the presence of mycelium was abundant in Tepetl at 17 °C, so it is considered susceptible to the pathogen. Atlixco showed low Mycelium content at 28 °C, which is considered tolerant. In plants with wilt symptoms and asymptomatic, tyloses formation and phenolic deposition compounds contribute to defense against P. cinnamomi. The selections of the Mexican race Tepeyanco,Atlixco and Tepetl showed resistance, probably because activated their structural histological mechanisms of defense and chemical prior to infection by P. cinnamomi.

Keywords : Persea americana Mill; histological defense; phenolic deposition; tyloses.