SEED TRANSMISSION OF PANTOEA-STEWARTII IN-FIELD AND SWEET CORN

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 inbre ds and two sweet corn cultivars that were inoculated with either a rif ampicin and nalidixic acid-resistant strain (rif-9A) or a wild-type st rain (SS104) of P. stewartii. Four additional seed lots were collected from naturally infected inbreds. Percentages of infected kernels rang ed from 0.8 to 72%, as determined by agar plating or by individual-ker nel enzyme-linked immunosorbent assay (ELISA). Plants grown from this seed were assayed by a stem-printing technique that consisted of cutti ng and pressing a cross-section of each stem onto agar media. Prints w ere examined for development of P. stewartii colonies after 24 and 48 h. The transmission rate from seed produced on the inoculated plants w as 0.066% (28 of 42,206 plants), based on all seedlings assayed. Trans mission was estimated to be 0.14% from infected kernels. The transmiss ion 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 = 0.03 4) from seed produced on naturally infected plants than from seed prod uced on inoculated plants, probably due to greater kernel damage cause d by ear shank inoculation. The rarity of seed transmission of P. stew artii from heavily infected seed lots that would ordinarily be rejecte d due to poor germination suggests that the likelihood of seed transmi ssion from good quality commercial seed corn is virtually nonexistent.