REACTION OF SWEETPΡΟΤΑΤΟ GENOTYPES TO Botryodiplodia theobromae Pat. and Macrophomina phaseolina Tassi

Abstract

Sweetpotato genotypes were screened for resistance to Botryodiplodia theobromae Pat. and Macrophomina phaseolina Tassi, the two major postharvest pathogens found infecting sweetpotato roots during storage in the Philippines. The effect of different stages of maturity of sweetpotato plants on host resistance and the nature of postharvest disease development were also investigated, Assessment of 437 genotypes for resistance to B. theobromae infection showed that 0.7% and 15% were highly resistant and resistant, respectively. Out of 434 genotypes evaluated for resistance to M. phaseolina only 0.2% and 6% were noted to be highly resistant and resistant, respectively. Majority of the genotypes screened against both pathogens were found to be moderately susceptible to susceptible. Roots taken from 3 months old plants were more resistant to infection by either B. theobromae or M. phaseolina than those taken from 4 and 5 months old plants. The resistant, moderately resistant, and susceptible lesion types were categorized based on visual and histological examinations. Ipomeamarone was detected in inoculated resistant, moderately resistant and moderately susceptible sweetpotato roots but not in susceptible roots. No visible formulation of ipomeamarone was noted in healthy uninoculated roots.