Detecção da diversidade e associação de Lasiodiplodia theobromae com o cajueiro utilizando marcadores microssatélites.

Abstract

The cashew crop is one of the most important agribusiness activity in northeastern Brazil, mainly due to its social and economic impact in that region. Nevertheless, severe outbreaks of gummosis and black branch dieback, both caused by the fungus Lasiodiplodia theobromae have imposed great losses under semi-arid conditions. Presently, these diseases are the most important ones over semi-arid conditions in Northeast Region. However, the limited amount of basic knowledge about population biology, genetic structure and pathogen, host and environment interaction are likely to hinder the efforts to manage this pathogen. This study was developed in order to establish a L. theobromae population associated with cashew plant from different ecological regions in the northeastern Brazil, to determine the survival endophytic ability of this fungus in cashew tissues and to characterize this population by using microsatellite markers. Initially, samples of cashew stems were gathered from three natural ecosystems in Brazil in order to isolate L. theobromae. A population of 41 isolates associated with cashew was obtained. Bioassays aiming to determine the surviving ability of this fungus in non infected tissues close to gummosis lesions were conducted using sampled stems. A subpopulation of 15 isolates of L. theobromae was used for DNA extraction followed by polimerase chain reaction (PCR) using 15 oligonucleotides primers designed to amplify microsatellites regions. PCR products were observed on agarose gel in ethidium bromide electrophoresis and analyzed by the unweighted pair-group method with arithmetic mean (UPGMA) by the Nei and Li similarity coefficient. L. theobromae was successfully isolated from cashew tissues as far as 90 cm from the border of the gummosis lesion in both up and down directions. This result confirms the endophytic behavior of this fungus in cashew plant. A great genetic variability of L. theobromae population was observed as determined by 16 similarities groups varying from 91% to 5%. None isolate achieved 100% similarity. The greatest similarity was found between pathogenic and endophytic isolates.