Peroxidase Activity, Isozyme Patterns and Electrolyte Leakage in Roots of Cocoyam Infected with Pythium myriotylum
Knowledge of host defence response in cocoyam against Pythium myriotylum is essential in understanding disease resistance and the development of effective control measures for the cocoyam root rot disease. Four cocoyam accessions were assessed for root rot disease reaction by inoculating the roots of intact plants in the greenhouse and detached roots in the laboratory with P. myriotylum isolate ‘Mamu’ from Cameroon. Electrolyte leakage in detached infected roots and peroxidase activities and isozyme expressions in crude protein extracts collected from healthy roots of inoculated and non-inoculated plants at 0, 2, 4, 6 and 8 days post inoculation (dpi) were used independently to assess resistance/tolerance. Based on the results, cocoyam accessions RO1054 and RO3015 were rated tolerant/moderately resistant while accessions RO2063 and ‘Local White’ (LW) were rated susceptible to P. myriotylum isolate ‘Mamu’. The time-course spectrophotometric analysis of peroxidase activity showed an increase in activity in the roots of the tolerant RO1054, 8 days after inoculation. One peroxidase isoform (Rf 0.66) was induced only in roots of the susceptible inoculated accessions ‘Local White’ and R02063 at 4 and 6 dpi. One acidic peroxidase isozyme (pI 4.5) and one basic isozyme (pI 7.4) were detected only in roots of inoculated plants. Our results suggest that electrolyte leakage in infected roots can be used to assess tolerance/susceptibility in cocoyam and that tolerance to the root rot disease in cocoyam may be associated in part with an increased generation of peroxidase activity in the roots.