PEST MANAGEMENT: DISEASES Infection of Plants of Selected Rice Cultivars by the False Smut Fungus, Ustilaginoidea virens, in Arkansas

False smut, caused by Ustilaginoidea virens, has recently been found in Arkansas. Plants infected by the fungus remain symptom-free until heading and it is difficult to see spores on contaminated seeds. Field tests were conducted in 2006 to determine the effect of false-smut inoculation of rice seeds on the yields of selected rice cultivars. Seeds were inoculated by vacuum infiltration in suspensions containing one million spores per ml. Spores were obtained from mature spore balls found on panicles collected in Arkansas in 2005. Infiltrated and control seeds were planted into large pots placed in pools at the Agricultural Experiment Station at Fayetteville in a randomized complete block design with four replications for each cultivar and treatment. The data were collected at maturity and included the number of panicles set per plant per treatment and the amount of blanking found on the panicles. Tissue samples were collected for PCR analysis to determine if plants were infected. The results of these experiments show that inoculation of seeds by infiltration reduced the number of panicles produced compared to control plants. While this work must be repeated, the current data suggest that the recognizable symptoms of infection in rice plants by U. virens are cryptic and should perhaps be expanded to include the deleterious effect on panicle production as a symptom of infection. These preliminary data suggest that current estimates of yield reductions based on the number of spore balls formed might be inaccurate. We propose that infection, with or without spore-ball formation, is deleterious to panicle formation and directly causes increased seed blanking. Early detection of the fungus in asymptomatic plants is warranted for timely application of fungicide to minimize yield reduction through chaffing and reduced panicle formation.