Aplicação da Microscopia Eletrônica de Varredura na Caracterização do Processo Infeccioso de Colletotrichum em Folhas de Clones de Cajueiro

Abstract

The cashew tree (Anacardium occidentale L.) is a tropical plant and is currently dispersed throughout Brazil. It is of great socioeconomic importance for the country, generating employment in industry and in the countryside. However, the productivity of this crop has limitations, among them, the occurrence of diseases, such as anthracnose, which has important infectious potential for a wide range of tropical fruit plants, being the main disease present in cashew orchards. Anthracnose can occur at any stage of plant development, causing severe damage. Therefore, in order to understand the infection process of the etiologic agent of anthracnose in commercial cashew cultivars, it is important to understand how the entire cycle of the disease occurs in plants. In this way, the scanning electron microscopy (SEM) emerges as a relevant tool used in the observation and characterization of fungal pathosystems. In this work the SEM comes to elucidate the foliar infection process of anthracnose of the cashew tree, through the characterization of the microstructure of the fungus and the damage and injuries caused by it in the host tissue. For this, two monosporic isolates of Colletotrichum, LF 200 and LF 201, were inoculated in leaf discs of three cashew genotypes CCP 09, CCP 73 and BRS 226, by means of spore suspension 2.1 x 106 spores/mL, in the time range from 0 hours to 144 hours. The results showed the formation of reproductive structures, nutrient absorption structures, fixation structures, germination, and primary and secondary infection structures. It was found that the isolates use natural openings to colonize the host's internal tissues, as well as punctual puncture through appressoria. It was also possible to observe the difference in the success of colonization and infection of isolates of the fungus in resistant genotypes. For a better understanding, it is still necessary to identify the isolates at the species level.