Studies on comparative response of two potato species (Irish potato – Solanum tuberosum and Sweet potato – Ipomea batatas) to three tuber rot pathogens, Botryodiplodia theobromae, Rhizopus stolonifer and Penicillium expansum. were carried out in Calabar, Nigeria. Results showed that within four weeks of the experiment, these pathogens consistently caused starch grain depletion from the tissues of the two potato species studied. The pattern of colonization differed between them. In the first week of incubation, B. theobromae caused a reduction of the size of the grains from 10mm to 5mm in S. tuberosum before digesting them. Less than 10% of the starch was lost; while S. stolonifer and P. expansum individually recorded 20% starch grain depletion within same period. In I. batatas, reduction in the size of the starch grains was only evident in R. stolonifer –treated tubers, with negligible loss recorded within this period (first week of incubation). By the 3rd week of incubation, R. stolonifer and B. theobromae had recorded total starch depletion in I. batatas tuber tissues. All the treatments except for P. expansum- treated I. batatas tissues recorded zero starch presence, extensive tissue necrosis and massive collapse of cell wall by the end of the 4th week of incubation. Differences in the sizes of starch grains were also observed in healthy tissues of the two potato species used in this study. The sizes of starch grains in I. batatas were smaller and more tightly packed than those found in S. tuberosum.
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