The 2009 ASHS Annual Conference

Charcoal rot caused by Macrophomina phaseolina is an important disease of soybean (Glycine max) in Illinois and can easily be isolated from most production fields in the state.  Although charcoal rot is generally thought to be a minor pathogen of pumpkins and other cucurbits, these vegetables are often included in the soybean rotational scheme and can possibly increase or maintain high inoculum levels for future soybean crops.  A greenhouse study was conducted to determine the reproductive ability of M. phaseolina on Cucurbita pepo  ‘Howden’ and ‘Sorcerer’, C. moschata ‘Libby’s Select’ and ‘Buckskin’, and C. maxima ‘Big Moon’  and ‘Mammoth Gold’ based on inoculation levels of  0, 10, 20, 50, and 100 CFU/g soil (or ~0, 6,000, 11,000, 29,000, 67,000 CFU/10 cm-dia. pot).  Although, no symptoms of charcoal rot were observed on pumpkin plants three months after inoculation, M. phaseolina readily colonized and reproduced on all cultivars.  No interaction was detected between inoculation level and cultivar, and no differences were observed between cultivars.  Results indicated that various species of pumpkins (Cucurbita spp.) provide excellent hosts for M. phaseolina and that if charcoal rot is a recurring problem on soybean, pumpkins should not be included in the rotation as they tend to increase the soil population densities of this soil-borne fungus.