Post-harvest enzymatic activities of healthy and infected Cassava (Manihot esculenta Crantz) tubers

Post-harvest rot of tubers of three cassava (Manihot esculenta Crantz) cultivars namely TMS 4(2)1425 (hybrid cultivar); and 2 local cultivars Oko-Iyawo and Odongbo) were surveyed in Southwestern Nigeria. A total of ten fungal organisms were isolated from rotted cassava tubers collected from eight towns in four states in Southwestern Nigeria. The most frequently isolated and pathogenic ones which were used in this study as the test pathogens are Lasiodiplodia theobromae: Macrophomina phaseolina; Rhizopus stolonifer; and Fusarium pallidoroseum.. Their cell wall degrading enzymes which are cellulase; amylase; polygalacturonase (PG); and pectin methyl esterase (PME) were also assayed. In all the three cultivars inoculated with each of the test pathogens, enzyme activities were found to increase with the incubation period between 6 and 8 days of inoculation and declined at day 10. The peak of enzyme activities declined at different periods for all the cultivars used. PME and PG activities were found highest in cultivar TMS 4(2) 1425 and least in Odongbo cultivar.Test pathogens also behaved differently when inoculated with the culture filtrates of the different enzyme activities. M. Phaseolina was found highest while F. pallidoroseum was the least in all the enzyme activities cultured except in pectin methyl esterase where Lasiodiplodia theobromae had the highest activity. Mycelia dry weight of the test pathogens were also found to increase with incubation period with F. pallidoroseum having the highest mycelia mats while L. theobromae had the least. Enzyme production and activities of the test pathogens in the utilization of the carbon sources varied with the different carbon sources and the test pathogens. All the test pathogens produced enzymes and had activity but at different levels.Generally, enzyme activities showed the rate of maceration of tissues and the extent of rot disease of cassava tubers as well as the aggressiveness and pathogenic abilities of the test pathogens.