Use of Leaf Temperature to Measure the Effect of Brown Stem Rot and Soil Moisture Stress and Its Relation to Yields of Soybeans. A. Mengistu, Postdoctoral Research Associate, Department of Plant Pathology, Seed and Weed Sciences, Iowa State University, Ames 50011. H. Tachibana, A. H. Epstein, K. G. Bidne, and J. D. Hatfield. Research Plant Pathologist, USDA-ARS, Professor, Agricultural Research Technician, and Former Agricultural Research Technician, Department of Plant Pathology, Seed and Weed Sciences, Iowa State University, Ames 50011. Plant Dis. 71:632-634. Accepted for publication 17 November 1986. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/PD-71-0632.

Soybean cultivars susceptible to brown stem rot and tested in soil infested with high and low levels of the causal fungus (Phialophora gregata) showed significant differences in leaf temperature minus air temperature (DT) with different degrees of moisture stress. Significant differences in DT occurred between 11:00 a.m. and 4:00 p.m. for five consecutive days during the R6–R7 growth stages on plants with higher levels of stem browning, with both moisture-stressed and nonstressed treatments showing the higher temperature. Plants exposed to a high level of inoculum in combination with moisture stress had higher DT values and had significantly lower yields than other treatments. However, neither moisture stress in combination with a low inoculum level nor low or high inoculum levels in environments without moisture stress resulted in reduced yields. Higher values of DT were consistently associated with increased levels of moisture stress but not with increased stem browning. Although differences in percentage of stem browning among treatments were observed, the differences were not always significant. DT was significantly, negatively correlated (r = –0.79) with yield but was not significantly correlated with stem browning and level of inoculum. DT provided a convenient indication of soybean yield reduction caused by a combination of moisture stress and severe Phialophora gregata infection.

Keyword(s): interactions.