Corn stunt disease complex increases charcoal rot ( Macrophomina phaseolina ) under field conditions

Maize production areas where corn stunt epidemics have been observed in the last three years exhibited severe symptoms of plant lodging. Consequently, plant lodging has been attributed to the causal agents of corn stunt disease complex. This study evaluated the association between corn stunting and charcoal rot diseases, and explained the occurrence of plant lodging in areas with a high incidence of corn stunting. Maize hybrid P30F53 VYH, which is susceptible to stalk rot and corn stunting, was sown in two areas. All maize plants from half of each experimental area were inoculated with the fungus of charcoal rot in corn, Macrophomina phaseolina. Corn stunting occurred naturally in the experimental areas, allowing the establishment of the following treatments: 1) inoculated with M. phaseolina and showing typical corn stunting symptoms; 2) inoculated with M. phaseolina and showing no symptoms of corn stunting; 3) not inoculated with M. phaseolina and showing symptoms of corn stunting; and 4) not inoculated with M. phaseolina and showing no symptoms of corn stunting. The incidence of early death was highest under combined infection (treatment 1). Plants with combined infection had 30% higher severity of charcoal rot in the inoculated internode that those with only charcoal rot. Plants with combined infection had 93.7% higher severity of charcoal rot in the internode above the inoculated internode and higher number of internodes with charcoal rot symptoms than those under other treatments. Plants with no disease had higher grain yield than those with isolated or combined infections. Combined infections resulted in reductions of all productivity components. For our knowledge this is the first scientific report showing that corn stunt disease complex increase stalk rot severity caused by M. phaseolina .