Effect of Compost Quality and Microbial Population Density of Composts on the Suppressiveness of Pythium myriotylum, Causal Agent of Cocoyam (Xanthosoma sagittifolium) Root Rot Disease in Cameroon

The effect of eight compost types made from four different grass species mixed with poultry and pig manure and microbial population in compost were evaluated on the suppressiveness of the root rot disease on cocoyam. The experimental layout was a complete randomized design with five replicates conducted in a screen house in the Faculty of Agronomy and Agricultural Sciences, University of Dschang. Compost was used in the ratio of 1:1 by weight (2kg compost: 2kg soil/plant). It was inoculated 48 hours before planting to enable compost-pathogen interaction. Compost microbial populations were estimated using dilution plating with appropriate media (tryptic soil agar, TSA) for Heterotrophic bacteria and Actinomycetes isolation agar for Actinomycetes respectively. The physicochemical properties (pH-H 2 O, CEC, N, K, Na, Mg and Ca) of compost were determined and analysed. Disease incidence and severity was significantly (P £ 0.05) reduced in all compost amended pots than the control at 12 weeks after inoculation. The density the microbial groups (Heterotrophic and Actinomycetes) reported to have contributed positively in the suppression of the disease. Microbial populations of Heterotrophic bacteria and Actinomycetes in the different compost types significantly influenced cocoyam root rot severity as the correlations were highly positively significant for Heterotrophic bacteria (R 2 = 0.911) and for Actinomycetes (R 2 = 0.862) respectively resulting to low root rot disease incidence and severity. The most suppressive compost was compost made of Tithonia diversifolia with the highest microbial populations irrespective of animal dung (34 x 10 11 /ml for poultry and 30 x 10 11 /ml for pig) which registered the least disease incidence and severity (24.5% and 8% respectively). Correlation analysis of physicochemical properties of compost revealed that disease suppression is associated with the activities of microbial populations and physicochemical qualities of compost.