|Johnson, D - UNIVERSITY OF MINNESOTA|
|Plaisance, K - UNIVERSITY OF MINNESOTA|
|Wyse, D - UNIVERSITY OF MINNESOTA|
Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: February 12, 1998
Publication Date: N/A
Technical Abstract: Inundative foliar application of Pseudomonas syringae pv. tagetis (Pst) in an aqueous suspension containing Silwet L-77 (0.3%) provides control of sunflower and Canada thistle but has no effect on soybeans. Apical chlorosis in host plants is due to the production of tagetitoxin by Pst. Factors regulating the efficacy of Pst on host (sunflower) and nonhost (soybean) plants were examined. Pst (1 x 109 cfu/ml) was sprayed on leaves of 8-day-old sunflower and soybean plants. Endophytic populations of Pst were determined following sterilization of the leaf surface. In the case of sunflower, a rapid increase in the endophytic Pst population occurred during the first 24 h after treatment, followed by a slow decline during the subsequent 48 h. When sprayed on developing soybean leaves, almost all of the applied Pst remained on the leaf surface. Preliminary results suggest that spray droplets were trapped on the leaf surface by trichomes. Rubbing the leaf surface of soybean with ethanol to remove trichomes prior to Pst application facilitated establishment of an endophytic Pst population, but at a lower density than that observed in sunflower leaves not rubbed with ethanol. The effect of injecting 500 ng of tagetitoxin into the cotyledons of 8-day-old sunflower and soybean was also investigated. Injecting tagetitoxin into sunflower cotyledons reduced chlorophyll content of developing leaves by approximately 90% after 72 h. In contrast, injecting tagetitoxin into soybean cotyledons resulted in less than a 50% reduction in chlorophyll content of the developing trifoliate after 120 h. The results suggest that soybean may not be injured by inundative foliar applications of Pst due to restricted entry of the bacterium into leaves and reduced susceptibility to tagetitoxin.