Characterization of the morphological response of susceptible and resistant varieties of cassava (Manihot esculenta Crantz) to vascular bacterial blight caused by Xanthomonas axonopodis pv manihotis

Xanthomonas axonopodis pv. manihotis is one of the major limitations for cassava cultivation. In the present study, optical microscopy was used to perform a comparative analysis of the morphological and histochemical changes in the stem of a susceptible (TMS60444) and a resistant (CM6438-14) cassava variety at 7 and 14 days after inoculation with the pathogenic strain CIO151. The resistant variety was detected to generate callose barriers on the cell walls of the cortical parenchyma and phloem, maintaining the functionality of this tissue. On the other hand, for the vascular tissues of the susceptible variety there is collapse in the phloem due to total obstruction by deposits of callose and phenolic compounds and in the xylem due to tylosis formation and/or phenolic compound accumulation, without stopping the progression of the systemic disease.

Callose deposits; tylosis; phenolic compounds; epifluorescence