ARBUSCULAR MYCORRHIZAL FUNGI IDENTIFICATION IN AVOCADO TREES INFECTED WITH Phytophthora cinnamomi RANDS UNDER BIOCONTROL

Abstract

Arbuscular mycorrhizal fungi presences in the rhizosphere of avocado trees with symptoms of root rot sadness caused by Phytophthora cinnamomi were determined. The investigation was done in the avocado orchard "Ojo de agua" in the town of Tancitaro, Michoacan, Mexico, in 21 previously selected trees. For the control of P. cinnamomi were applied three strains of Trichoderma (T. erinaceum, T. aggressivum and T. arundinaceum) before the application was made the first soil sampling, the second 6 months later, before the second application of Tricoderma strains and the last 12 months before the third application. To remove soil spores was used wet sieving and decantation protocol proposed by Gerdemann and Nicolson (1963), followed by centrifugation on sucrose (400 g L-1) at 2000 rpm. Taxonomic identification was based on the morphological characteristics of AMF spores, considering the shape, size and color, and thickness, ornamentations and number of the layers of the wall, coupling form and supporting hyphae, identifications were made by comparison with original descriptions available in the International Collection of Arbuscular Mycorrhizal Fungi and Glomeromycota species list. The first sampling were identified eleven species in seven genera: Glomus with two undetermined species, Glomus sp.1, Glomus sp.2, Glomus etunicatum and Glomus geosporum; genus Acaulospora, one undetermined species Acaulospora sp., A. spinosa, A. bireticulata and A. denticulate; genus Entrophospora, E. infrequens; genus Diversispora, D. aurantia; genus Scutellospora, S. pellucida; genus Racocetra, R. castanea and R. verrucosa and genus Gigaspora, Gi. decipiens. In the second and third sampling, the presence of new kinds of HMA there was not observed but the number of spores increased (average 38.09% and 30% respectively). The application of these species in the genus Trichoderma to control root pathogens of avocado encouraged the growth of HMA spores in the rhizosphere of the crop.