USDA-ARS North Central Regional Plant Introduction Station
Department of Plant Pathology
Department of Plant Pathology and Seed Science Center, Iowa State University, Ames 50011
Seed transmission of Pantoea stewartii was evaluated by assays of more than 76,000 plants in greenhouse and field grow-out trials. Fourteen P. stewartii-infected seed lots were obtained from two dent corn inbreds and two sweet corn cultivars that were inoculated with either a rifampicin and nalidixic acid-resistant strain (rif-9A) or a wild-type strain (SS104) of P. stewartii. Four additional seed lots were collected from naturally infected inbreds. Percentages of infected kernels ranged from 0.8 to 72%, as determined by agar plating or by individual-kernel enzyme-linked immunosorbent assay (ELISA). Plants grown from this seed were assayed by a stem-printing technique that consisted of cutting and pressing a cross-section of each stem onto agar media. Prints were examined for development of P. stewartii colonies after 24 and 48 h. The transmission rate from seed produced on the inoculated plants was 0.066% (28 of 42,206 plants), based on all seedlings assayed. Transmission was estimated to be 0.14% from infected kernels. The transmission rate from seed produced on naturally infected plants was 0.0029% (1 of 34,924 plants), based on all seedlings, and 0.022% from infected kernels. Seed transmission occurred significantly less often (P = 0.034) from seed produced on naturally infected plants than from seed produced on inoculated plants, probably due to greater kernel damage caused by ear shank inoculation. The rarity of seed transmission of P. stewartii from heavily infected seed lots that would ordinarily be rejected due to poor germination suggests that the likelihood of seed transmission from good quality commercial seed corn is virtually nonexistent.