Endophytic diversity in Persea americana (avocado) trees and their ability to display biocontrol activity against Phytophthora cinnamomi

Plants host a variety of endophytic microorganisms that can promote growth and protection against pathogens. Endophytes have been widely investigated in plants and used in biological control of plant pathogens. However, little is known about the diversity of endophytes in Persea americana Mill. (avocado) roots and their potential role in biocontrol of Phytophthora cinnamomi (Pc). This Oomycete is the causal agent of Phytophthora root rot, the most important disease in avocado producing countries worldwide. This study aimed to identify potential biocontrol agents from avocado roots and to use selected endophytes with biological activity against P. cinnamomi in vivo. The identification was based on morphological characteristics of the isolates as well as using ITS, β -tubulin, EF-1α and 16S ribosomal RNA gene sequencing. Twenty four different fungal species and 8 bacterial species were identified as endophytes from the roots of avocado plants from various locations in South Africa. Two fungal strains and 2 bacterial strains were selected on the basis of their in vitro antagonistic activity against P. cinnamomi. Clonal as well as endophyte-free tissue-cultured avocado plants were inoculated with each of the selected endophytes at 10 6 spores ml -1 for fungi and 10 8 CFU ml -1 for bacteria. After 4 weeks of inoculation, each plant received 10 5 Pc zoospores ml -1 directly sprayed onto roots, except for negative control plants. Positive control plants received no endophytes. Disease symptoms were assessed 21 days post infection and disease incidence was calculated. Avocado plants that received endophytes prior to Pc- infection showed a significant decrease in disease incidence with ratings from 2-40% compared to 94-100% for the positive control plants. Resumen