Screening Cowpea Cultivars for Resistance to Charcoal Rot (Macrophomina phaseolina) for Organic Production.

Charcoal rot [Macrophomina phaseolina (Tassi) Goid.] is a fungal disease that is economically important to many host plant species. Cowpea (Vigna unguiculata L. Walp.) is an important warm-season legume forage, grain, vegetable and cover crop for many regions of the globe and is one of the host species for M. phaseolina. Efforts have been made to breed genetic lines that are resistant to M. phaseolina but little research has been done to screen cowpea cultivars for resistance, an important consideration for cultivar selection for organic production. Our results indicated that two of 26 screened cultivars, ‘IT85F-867-5’ and ‘IT98K-589-2’, displayed the highest stand density in both the field trial and the greenhouse trial, suggesting they may be resistant to M. phaseolina in seedling and vegetative growth stages. Later maturing cultivars, such as ‘Iron & Clay’ and ‘US1136’, may also withstand infection from M. phaseolina to produce grain or forage yields due to known genetic resistance or physiological mechanisms involved in plant aging. ‘C.T. Pinkeye’ and ‘Coronet’ displayed the highest rates of infection based on a colony forming unit index and intensity of root and stem discoloration indicating that their physiology may provide a more desirable environment for microsclerotial growth later in the season.