Screening Progenies of Mexican Race Avocado Genotypes for Resistance to Phytophthora cinnamomi Rands

Because of the low availability of avocado rootstocks with resistance to Phytophthora cinnamomi, it is necessary to search for genotypes that offer resistance and that could be used as commercial rootstocks. The objective of this study was to select progeny from the genotypes of Mexican race avocado plants that are resistant to P. cinnamomi. Seedlings from 12 avocado genotypes were placed in containers inoculated with a mycelial suspension of P. cinnamomi. Signs of disease in the upper part of the seedlings were registered every 3 days for 8 weeks using a visual scale of damage severity. The chi(2) test (P < 0.009) showed significant differences among the genotypes evaluated, with 'Todo el Ano' being the most resistant, as demonstrated by its rating of 70% asymptomatic seedlings, followed by 'Platano' with 40%. The most susceptible genotypes were 'Maria Elena', 'Silvestre', and 'Hass', with 100% mortality. Seedling inoculation facilitated the detection of resistance to P. cinnamomi. 'Todo el Ano' showed resistance toward P. cinnamomi. Therefore, individuals of its offspring could be recommended for use as rootstocks after confirming their resistance with a second evaluation, as well as performing tests in multiple localities to demonstrate their productive behavior after grafting.