Plant-Based Culture Media for Improved Growth and Sporulation of Cercospora janseana.

Cercospora janseana is the causal agent of narrow brown leaf spot, one of the major diseases of rice in the United States. In vitro studies were conducted to evaluate various plant-based agar media in comparison with potato dextrose agar (PDA) for their effects on radial growth and sporulation of C. janseana. The agar media were evaluated individually with the following plant-extract ingredients: fresh rice leaves, dried rice leaves, dried rice stems, dried rice roots, dried rice hulls, dried rice straw, rice bran, dried sorghum leaves, and dried barnyard grass leaves. Plant-based extracts obtained from 25, 50, 100, or 200 g/liter (plant material/water) were tested either alone or in combination with 10 and 20% clarified V8 juice. PDA served as the control medium. Media with 10 and 20% V8 juice were also included for comparison. Media were inoculated with a disc of 1-week-old actively growing C. janseana at the center of Petri plates and incubated at 28°C with a 12/12-h (light/dark) cycle for 2 weeks. Radial growth was measured at 7 and 14 days after inoculation (DAI), whereas sporulation was measured at 14 DAI. Radial growth and sporulation differed among various media and their amendment concentrations. Media with extracts of fresh rice leaves, dried rice leaves, dried rice stems, dried barnyard grass leaves, and clarified V8 juice enhanced radial growth compared with the PDA control. Of all the agar media evaluated, fresh rice leaf extract amendment at 25 g/liter with no V8 supplementation consistently supported the greatest radial growth, and 10% V8-only medium resulted in greater sporulation of C. janseana than other media evaluated.