Epiphytic Movement and Survival of Pseudomonas syringae on Spring Wheat

Field, greenhouse, and growth chamber experiments demonstrated that Pseudomonas syringae, the incitant of bacterial leaf necrosis of wheat, moved from inoculated wheat seed to the seedling and survived as an epiphyte on the leaves. In greenhouse experiments 80-90% relative humidity favored movement of P. Syringae to the coleptile and first true leaf of the seedlings. Movement was not different on wheat cultivars susceptible or resistant to bacterial leaf necrosis. Under 70-98% relative humidity in a growth chamber, P. syringae moved to a significantly higher (P=0.01) percentage of seedlings at 10C than at 16 or 22C. In a field experiment, using serotype VI as a marker, P. syringae was recovered from the first true leaf, but not from upper leaves up to 41 days after emergence. From date of seedling emergence to day 41, total precipitation received was only 1.09 cm. However, after substantial rainfall (3.48cm) on day 42, P. syringae serotypes III, IV, and V in addition to VI, were isolated from upper leaves in both inoculated and control areas. This suggests that other sources of inoculum or bacterial leaf necrosis were also present.