Cytological aspects of compatible and incompatible interactions between cashew (Anacardium occidentale L.) seedlings and isolates of Colletotrichum gloeosporioides (Penz.) complex

A strategy in the control anthracnose of cashew (Anacardium occidentale L.) is the management of crop phenology and defense mechanisms of this host. In previous studies, under controlled conditions, the seedling reactions of 5 cashew clones (CAP-14, CCP-06, CCP-09, CCP76 and CCP-1001) to 36 isolates of Colletorichum gloeosporioides Penz. complex (LARS- 905 to 940) was evaluated. However, good field management requires information about the infection process. This research aimed to clarify cytophysiological aspects of three compatible interactions of this pathosystem (isolates LARS-905 and 910 × CCP-76; LARS-910 × CCP-1001) and an incompatible one (LARS-905 × CCP-1001), using infected leaves/stems and microscopy (light, scanning and transmission electron). No significant differences were found prior to penetration. In the susceptible combinations, 36-66 h after inoculation, a thin primary hypha (TPH) formed in the invaded epidermal cell, widening as a large primary hypha (LPH), which filled the cell lumen simultaneously with accumulation of of yellow-brown lignopolysaccharides. Then, a thin secondary hypha (TSH) developed from the LPH, penetrating adjacent cells before the first became necrotic. In the incompatible interaction, the response of the first invaded cell was faster and more intense, with formation of papilla and lignopolysaccharide-protein-silicon complex usually blocking the pathogen.