Analysis of suppressive soils and development of biological control methods for Phytophthora root rot of avocado.

Abstract

Phytophthora root rot (PRR) of avocado (Persea americana), caused by Phytophthora cinnamomi, is a serious problem in California despite current approaches to disease control that include chemical fungicides, resistant rootstocks, and cultural methods. The current trend toward increasing restrictions on the use of chemical pesticides threatens to eliminate any benefits these materials may provide. This research project was initiated in response to the need for effective alternative approaches to control PRR that will shift the emphasis away from chemical fungicides. Our approach was to identify sites in which replants or older avocado trees were growing well despite the presence of P. cinnamomi in these or neighboring groves. Soils from these suspected PRRsuppressive sites were investigated as possible sources for biological control agents. Some of these soils have suppressed PRR in greenhouse experiments. Microorganisms isolated from these soils have reduced disease of test plants caused by P. cinnamomi in our greenhouse tests.