Effects of compost amendment and the biocontrol agent Clonostachys rosea on the development of charcoal rot (Macrophomina phaseolina) on cowpea

Macrophomina phaseolina is a destructive pathogen causing charcoal rot of cowpea and other crops in the semi- arid areas of the Sahel (north-west Africa). Chemical management is not feasible in conditions of subsistence farming, and the plurivorous nature of the fungus limits the effectiveness of some cultural methods. This study aimed at identifying the effects of composting on the survival of M. phaseolina and of soil application of compost alone or in combination with the biocontrol agent Clonostachys rosea on inoculum density of M. phaseolina and on cowpea production. Inside the compost heap with diseased cowpea residues, the temperature reached 52 to 60°C and completely destroyed M. phaseolina microsclerotia. Addition of compost to planting holes significantly suppressed charcoal rot disease. Among the doses tested 6 tonnes of compost alone or supplemented with 50 kg NPK ha-1 resulted in 28-45% lower Area-Under- the-Disease-Progress-Curves (AUDPC) and 43-66% higher cowpea production. The addition of compost combined with C. rosea in the planting holes reduced the AUDPC up to 4-fold and increased the grain yield 2-5- fold. The best treatment was a mixture of two C. rosea isolates and the compost.