Incidence and Survival of Cylindrocladium parasiticum in Peanut Seed

Sixty-three commercial seed lots of peanut produced in Virginia were examined for the presence of seed with speckled testae. Speckled seed were present in seed lots from the 1998, 1999, and 2000 growing seasons at average rates of 3, 1.2, and 0.6%, respectively. Speckled and normal seed from 19 seed lots were assayed on a medium selective for C. parasiticum. The fungus was isolated from speckled seed at rates ranging from 40 to 96%. C. parasiticum was isolated only from a single normal seed from one seed lot. The pathogen was recovered at high rates from speckled seed immediately after pods had been dried in commercial drying trailers at temperatures up to 35°C. Ambient temperatures during winter seed storage that fluctuated from -10 to 28°C in 1999 and -8 to 33°C in 2000 greatly reduced pathogen recovery in speckled seed stored for 16 or 24 weeks. In field plots with naturally infested soil, the number of speckled seed harvested was directly correlated to the number of symptomatic plants in plots on 29 September. Based on this finding, the harvest of seed peanuts in areas of a field with high incidence of Cylindrocladium black rot (CBR) should be avoided. Adoption of this policy is expected to lower the number of speckled seed entering commercial seed lots and reduce the risk for spread of CBR.