Location: Foreign Disease-Weed Science
Title: Effects of frequency of extreme temperature highs on development of soybean rust Authors
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 6, 2013
Publication Date: June 17, 2013
Citation: Bonde, M.R., Nester, S.E., Berner, D.K. 2013. Effects of frequency of extreme temperature highs on development of soybean rust. Phytopathology. 103:708-716. Interpretive Summary: Soybean rust is a very important disease of soybean. In 2004, soybean rust was discovered for the first time in the United States (U.S.). Previous predictions suggested that if the disease ever reached the U.S., the environment would allow significant crop losses. However, in spite of dire predictions, the disease has remained relatively minor. As a result we decided to determine why the disease has remained at low levels. Infected soybean plants were placed in environmental chambers that simulated typical temperature conditions in southeastern U.S. We found that if the temperature reached or exceeded 94 degrees F for three or more consecutive days, disease was severely restricted. Because this temperature frequently occurs throughout southeastern U.S. during summer months, we conclude that high temperature is a major reason for little disease. The absence or delay of the disease in the southeastern U.S. has implications far beyond local production. Because the soybean rust pathogen cannot survive winters in the mid-western and northern U.S., the disease must first occur in the southeastern U.S., and then move northward if the disease is to affect the northern soybean growing regions. An understanding of how temperature affects soybean rust development takes on great importance and could lead to improved prediction models; thus reducing or possibly eliminating fungicide use.
Technical Abstract: Previously, we hypothesized that summer extreme diurnal temperature highs in the southeastern U.S were responsible for the absence or delay of soybean rust development until fall. In a temperature-controlled growth chamber study, a diurnal temperature pattern of 33 degrees C high/20 degrees C low reduced the number of urediniospores by 81 percent of that under optimum temperature conditions. In this present study, a temperature high of 35 degrees C for 1 hour on three consecutive days, initiated following lesion formation, reduced urediniospore production by 50 percent, and required approximately nine to 12 days for sporulation to resume once the extreme diurnal temperature highs ceased. Furthermore, three consecutive days in which the temperature high was 37 degrees C, beginning immediately after inoculation and subsequent dew period, reduced the number of lesions by 60 percent. The combined effects of reduced numbers of lesions and fewer urediniospores produced per lesion, caused by these high temperature peaks can account for the observed absence or delay of soybean rust development in the field in southeastern U.S. until cooler fall months. This is the first report showing the effect of frequency of extreme diurnal temperature highs on development of soybean rust.