Tissue masceration and starch depletion caused by some rot pathogens of cassava (manihot esculenta crantz)

Investigations on the anatomical damage of cassava caused by Botryodiplodia theobromae, Rhizopus stolonifer and Penicilliun expansum was carried out in Calabar, Cross River State, Nigeria. Inoculated and uninoculated cassava tissues were treated, sectioned weekly for four weeks and photomicrographs taken. The plates revealed massive cell wall macerations and depletion of starch grains in the samples infected with test pathogens. All the pathogens caused fragmentation of starch grains accompanied by minimal damage to infected cells and slight loss of starch grains in the first one week of incubation. The pattern of starch grain depletion adopted by P. expansum was from the lumen of the cell towards the cell boundaries thereby, creating empty spaces at the central portion of the affected cells. From the 3rd week of infection, massive cell wall degradation and starch grain depletion was evident. B. theobromae and P. expansum, in addition to starch depletion caused massive collapse of cell wall structure. R. stolonifer caused extensive necrosis, starch depletion and minimal collapse of cell wall structure particularly in the 4th week of incubation. Of the three pathogens studied, B. theobromae was the most aggressive in causing tissue damage and starch depletion in cassava tissues.