Effects of temperature on urediniospore germination, germ-tube growth, and initiation of infection in soybean by phakopsora isolates

Authors: Bonde, Morris; Berner, Dana; Nester, Susan; Frederick, Reid

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2007
Publication Date: 8/1/2007
Citation: Bonde, M.R., Berner, D.K., Nester, S.E., Frederick, R.D. 2007. Effects of temperature on urediniospore germination, germ-tube growth, and initiation of infection in soybean by phakopsora isolates. Phytopathology 97:997-1003

Interpretive Summary: Little information exists on effects of temperature on initiation of infection in soybean by the soybean rust pathogens. Temperature requirements are critical to disease development, and knowledge of these requirements is desired in order to assist farmers in determining whether or not to apply fungicides to control rust. In this study, isolates of the pathogen collected as long as 21 years ago were compared to recently collected isolates from South America and from Africa. All isolates were compared as to how temperature affected germination of the spores, germ-tube growth, and initiation of infection. Remarkably, each isolate behaved in a similar manner, suggesting that the pathogen has changed little in the past two decades. The information suggests that previously developed models will still be applicable in predicting disease.

Technical Abstract: Effects of temperature on urediniospore germination and germ-tube growth were compared among four isolates of Phakopsora pachyrhizi, one each from Taiwan, Zimbabwe, Hawaii, and Brazil, in addition to an isolate of P. meibomiae from Puerto Rico. Also compared were the effects of temperature during a nighttime dew period on initiation of infection in soybean by the isolates of P. pachyrhizi from Taiwan, Zimbabwe, and Brazil. All Phakopsora isolates behaved similarly as to how temperature affects urediniospore germination, germ-tube growth, and initiation of infection. Optimum temperature ranges were the same for germination, germ-tube growth, and infection, occurring from 17 to 28 deg C, regardless of rust isolate. Optimum temperatures for germination varied from 20 to 22 deg C, and for germ-tube growth from 19 to 21 deg C, depending on rust isolate and duration of incubation. Differences between specific isolates in optimum temperature for germination were sometimes statistically significant, but minor. Differences in optimum temperature for germ-tube growth were not significant. Results from this study show a close similarity exists in optimum temperatures for germination, germ-tube growth, and initiation of infection among four isolates of P. pachyrhizi and one of P. meibomiae, in spite of the fact that they had been collected from different parts of the world over a 21-year period.