Biocontrol microorganisms will be isolated from hyphal and chlamydospore baits using P. Gradations of suppressiveness in soils will be induced via heat treatments, antibiotic or chemical treatments, size screening and dilutions in order to correlate soil suppressiveness with isolated microorganisms. Populations of Phytophthora cinnamomi exist, but no disease symptoms are observed on avocados growing in those soils. Suppressive soils are identified as soils in which hyphal mats or chlamydospores of Phytophthora cinnamomi are severely degraded within 8 days, or they are soils in which substantial Cooperators from the New Guinea region will supply us with suppressive soil samples. Evidence indicates Phytophthora cinnamomi originated in the Papua New Guinea region, and so natural enemies may be abundant there. Microbial biocontrol agents for Phytophthora cinnamomi will be gathered from suppressive soils, recent root rot epidemics, foreign exploration and commercial sources. Several of these rootstocks are currently being patented for commercial use. Currently there are 34 trials with 53 different rootstocks being monitored in Southern California. Soil analysis and leaf nutrient analysis are performed on each trial. They are assessed yearly for survival, health, growth, yield, salt tolerance and other diseases.
Field tests are randomized blockĭesigns with 20 replicate avocado trees planted into Phytophthora cinnamomi infested soil. Rootstock varieties reaching the final selection stages will be field-tested. Selected rootstock varieties will be screened for resistance types, such as rapid root growth, inhibitory root exudation, preformed chemicals and phytoalexins. Potential rootstocks will be screened for general resistance to Phytophthora cinnamomi in infested greenhouse beds. Methods will employ novel, field isolation blocks of root rot resistent avocado varieties, collected from all over the world, and specific pollination via bees to induce desired crosses with harvested pollen. Avocado germplasm will be selected, bred and screened for resistance to Phytophthora cinnamomi root rot. Specifically here in California, Phytophthora root rot is the limiting factor in avocado production and now affects 60 to 75% of California groves. Project Methods Phytophthora cinnamomi is one of the most important root disease pathogens in the world.
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