Epiphytic Movement and Survival of Pseudomonas syringae on Spring Wheat

FRYDA, S. J., and J. D. OTTA. 1978. Epiphytic movement and survival of Pseudomonas syringae on spring wheat. Phytopathology 68:1064-1067. Field, greenhouse, and growth chamber experiments seedlings at 10 C than at 16 or 22 C. In the field, with a demonstrated that Pseudomonas syringae, the incitant of serotype VI isolate as a marker, seedborne P. syringae was bacterial leaf necrosis of wheat, moved from inoculated recovered from Bounty 208 wheat first true leaves, but not wheat seed to the seedling and survived as an epiphyte on the from upper leaves up to 43 days after emergence. From date leaves. In greenhouse studies, 80-98% relative humidity of seedling emergence to day 41, total precipitation received favored movement of P. syringae to aerial parts of the was only 1.09 cm. After a rainfall of 3.48 cm on day 42, other seedlings. Movement was not different on wheat cultivars P. syringae serotypes (Ill, IV, and V) were isolated from susceptible or resistant to bacterial leaf necrosis. Under 70upper leaves. This suggests that other sources of inoculum for 98% relative humidity in a growth chamber, P. syringae bacterial leaf necrosis also were present. moved to a significantly higher (P = 0.01) percentage of A leaf necrosis incited by the bacterium, Pseudomonas populations of P. syringae on hairy vetch and subsequent syringae van Hall, has been widespread on certain spring outbreaks of bacterial brown spot of bean in adjacent and winter wheat (Triticum aestivum) cultivars in South fields. Others also have suggested that epiphytic Dakota from 1968 to 1974 (13, 14). Outbreaks of this populations of P. syringae can be a source of diseasedisease were reported in Minnesota (21) and Montana inciting inoculum (1, 2, 4, 20). The ability of (19) in 1975. Bacterial leaf necrosis probably is more phytopathogenic bacteria to move from inoculated seed prevalent than has been reported since P. syringae has to the aerial parts of the seedling and become part of the been isolated from winter wheat seed from Nebraska, epiphytic microflora also has been demonstrated (9). North Dakota, South Dakota, and the Canadian The objective of this investigation was to determine if provinces of Alberta and Saskatchewan (13, 15). P. syringae from artificially contaminated seed could The etiology of bacterial leaf necrosis was unknown become established as an epiphyte on the aerial parts of until 1972 when Otta (13, 14) determined that P. syringae wheat seedlings and, if so, to determine what influence was the incitant. In Minnesota, Sellam and Wilcoxson relative humidity (RH), temperature, and cultivar (21) also identified the bacterium isolated from blighted susceptibility to bacterial leaf necrosis might have on wheat leaves as P. syringae. bacterial movement to the seedling. Little is known about the epidemiology of bacterial leaf necrosis. Widespread outbreaks have appeared suddenly MATERIALS AND METHODS while the wheat is in the boot stage. Severity of the disease in South Dakota seems to be linked with the amount of Wheat seed inoculation.-A P. syringae serotype VI wind-driven rain received in the last week of May and the isolate (15) from diseased wheat leaves (culture number first 3 wk of June (14). 488-J. D. Otta, Plant Science Dept., South Dakota State In recent years, resident epiphytic populations of P. University, Brookings, SD 57007) was grown on King's syringae have been detected on many host and nonhost medium B (MB) (7) for 24 hr and then suspended in sterile plants (1, 2, 4, 5, 18, 20). Under field conditions deionized water at a concentration of about 1 X l0' pseudomonads identified as being either P. syringae or a cells/ml. Wheat seed was placed in the suspension under closely related species have been isolated from apparently vacuum (produced by a water aspirator) for 5 min, and healthy plants such as peach (3, 4), cherry (1, 2), pear (18), then air dried. The inoculated seed was used in apricot, almond, olive, rose, juniper (4), soybean (12), greenhouse, growth chamber, and field studies to tomato (20), and certain weeds (4, 5, 20). Ercolani et al. (5) determine movement of seedborne P. syringae to the established a correlation between large epiphytic seedling. Isolations from wheat seedlings.-Two methods were used to isolate P. syringae from wheat seedlings and ooo32-949x/78/o0o0 1 85$o3.0o/olevsOnmehdivldtruaigalafote Copyright © 1978 The American Phytopathological Society, 3340 leaves. One method involved triturating a leaf or the Pilot Knob Road, St. Paul, MN 55121. All rights reserved. excised aerial part of a seedling in three drops of sterile