FUNGI PATHOGENICITY TEST IN ‘HASS’ AVOCADO PLANTS RELATED TO AMBROSIAL COMPLEXES

Abstract

Background: recently there has been concern for the monitoring of ambrosial complexes in Mexico that consist of a symbiotic relationship between a beetle and fungi, where the female invades a wide variety of species making galleries in the bark and wood, in which beetles reproduce and grow the fungi to feed the colony, these fungi can be a phytopathogen that can cause serious damage in the infected trees. The proximity of Raffaelea lauricola now present in Texas and the presence of Fusarium euwallacea in the north of Mexico; fungi that have caused great losses in the United States, put in risk the avocado production zones in Mexico. Consequently, the report of new fungi related to ambrosial complexes is of great importance. Objective: to carry out pathogenicity tests of fungi related to ambrosial complexes in avocado ‘Hass’. Methodology:  Isolates of Raffaelea brunnea, Ceratocystiopsis sp. (pre-identified) and Fusarium sp., from avocado trees parasitized with ambrosial beetles from the state of Michoacán and an unidentified fungus from Chiapas (Mexico) were used. Artificial inoculations with the fungi were carried out by wounds in mature stem and shoots of the growth of the year (young) of ‘Hass’ plants, and the symptoms and the progress of the damage within the stem were evaluated. Three of the isolates underwent a molecular identification analysis with the complete region of the ITS internal transcript space. Results: the fungus Ceratocystiopsis sp. was identified as Ophiostoma sp. and Fusarium sp. such as Fusarium solani, both isolated from Michoacán. While the Chiapas fungus was identified belonging to the genus Fusarium. After inoculation, R. brunnea and Fusarium sp. stood out in pathogenicity, with greater advancement within the stem and damage that in some cases reached the pith tissue, showing leaf wilting and reddish-brown staining inside the stem. These two fungi showed differential damage progression behavior according to the type of maturity of the tissue, where Fusarium sp. advanced more in the young tissue and R. brunnea in the mature one. Implications: it is proposed to consider that the study was only carried out in ‘Hass’, thus this may be an important factor, since probably if the fungi were inoculated in more varieties, differences in behavior of the advance in damage of these could be found. Conclusions: all the fungi showed to be pathogenic with variation in severity. In terms of Raffaelea brunnea, a peculiar behavior was found in the severity of internal and external damage, in which external symptoms may or may not occur, strictly in ‘Hass’ avocado plants 30 days after inoculation.