Sand and wind damage may facilitate entry of Corynebacterium michiganense ssp. nebraskense cells into maize seedlings. To test this hypothesis, wind tunnel experiments were conducted courtesy of the U.S.D.A. Wind Erosion Research Unit at Kansas State University. Fourteen day old seedlings of Mo17 x B73 (resistant) and A632 x A619 (susceptible) were given three treatments: 1) wind only, followed by spray inoculation; 2) sand abrasion followed by spray inoculation; and 3) abrasion with sand containing inoculum. Seedlings were exposed to sand abrasion for 10 minutes at a rate (31 grams/cm width/minute) that simulates erosion before thunderstorms. Spray inoculation consisted of applying 5 ml of inoculum. (2 x 108 colony forming units/ml) per pot of three seedlings. The sand/inoculum mixture contained one ml of inoculum per 115 grams of sand. Both wind and sand treatments followed by spray inoculation resulted in infection and expression of disease symptoms in susceptible A632 x A619 seedlings. C. m. ssp. nebraskense colony forming units (CFU) were isolated from plants exposed to these treatments. The wind treatment caused damage to leaf tips, which may have allowed bacterial cell entry. Sand treatment damaged both leaf tips and leaf surfaces, which caused inoculum droplets to adhere to the leaf surface. The sand/inoculum treatment did not produce disease symptoms in the susceptible A632 x A619 seedlings. The resistant Mo17 x B73 did not express symptoms after all treatments.
This experiment was repeated with the following changes: all plants were staked before treatment to assure contact of the sand with the plants, genotypes used were A632 x A619 and A632, bacterial inoculum concentration was increased to 2 x 109 CFU/ml, and 1 ml per 125 grams of sand were mixed together for the sand/inoculum treatment. Fourteen days after the treatments, there were no distinct disease symptoms on any of the plants. C. m. ssp. nebraskense CFU were isolated from plants that received the wind followed by spray inoculation treatment and from plants that received the sand abrasion followed by spray inoculation treatment. Bacterial CFU were not isolated from plants that received the sand abrasion/ inoculum mixture treatment. This experiment was still in progress at the time this report was submitted. The results of these experiments indicate that both wind and sand damage may facilitate entry of C. m. ssp. nebraskense cells into maize seedlings. Planned experiments are designed to evaluate the effect of higher levels of inoculum for the sand/inoculum treatment.
T. R. Rocheford, A. K. Vidaver, C. O. Gardner and D. L. Armbrust
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