Transmission of Erwinia stewartii through seed of resistant and susceptible field and sweet corn

Plant-to-seed and seed-to-seedling transmission of Erwinia stewartii was evaluated while considering the influence of resistant and susceptible seed parents. Leaves of 20 sweet corn (Zea mays) hybrids and eight dent corn inbreds were inoculated weekly from the three- to 10-leaf stage in 1992 by the pinprick method with a rifampicin-resistant strain or wild-type strains of E. stewartii. In 1993, leaves of four sweet corn hybrids and eight dent corn inbreds were inoculated by the pinprick method, and inoculum also was injected into ear shoots, ear shanks, or silk channels of selected plants. Seed from inoculated plants were harvested at maturity and assayed for E. stewartii. Seed and seed leachates were plated on nutrient broth yeast extract (NBY) agar amended with rifampicin, and leachates were inoculated into the susceptible sweet corn hybrid Jubilee in a greenhouse assay. Erwinia stewartii was detected in seed produced in 1992 on four hybrids, 89-3889, 88-2757, 91-1209, and 91-1574, which had systemic Stewart's wilt following leaf inoculation. The bacterium was not detected in seed from hybrids or inbreds with nonsystemic Stewart's wilt. In 1993, E. stewartii was isolated from cob and shank tissues and from seed of plants inoculated in ear shoots, ear shanks, or silk channels. Erwinia stewartii was recovered in 2 to 5% of leachates from individual seed of Jubilee inoculated in ear shanks and silk channels and from 1 to 16% of leachates of individual seed of FR632 inoculated in ear shanks and silk channels. There was no evidence of seed-to-seedling transmission of E. stewartii when over 75,000 seed from infected plants were planted in field or greenhouse trials. This may have been due, in part, to low rates of plant-to-seed transmission in seed produced on plants that were not systemically infected.