Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/1995
Publication Date: N/A
Interpretive Summary: Red leaf blotch, caused by the fungus Dactuliochaeta glycines attacks leaves of soybeans. The disease was first reported in Africa in 1957 and has been documented in only a few African countries. The fungus is soilborne. Field studies on red leaf blotch have been limited and reliable methods to assess the disease are critical to adequately evaluate soybean resistance and to understand the relationship of disease to yield. In this study, two field experiments were conducted in Zambia in each of two seasons. Disease severity or intensity was greatest on leaves lowest in the canopy. Yield losses ranged from 8 to 37%. In experiment two, one cultivar was either fungicide-sprayed at different times or not sprayed. The accumulated disease values over the season differed by the number of fungicide applications. Even one application of fungicide reduced the level of disease and increased yields by 18% over non sprayed plots. This study reports information about a potentially devastating soybean disease and provides significant information about how the disease develops on soybean plants and how the disease could potentially be controlled. These findings should be useful to researchers working on disease management in soybean production.
Technical Abstract: Red leaf blotch of soybeans, caused by Dactuiochaeta glycines, was evaluated on soybean plants in field plots located in Zambia. Two experiments were conducted in each of two seasons. Experiment one had four cultivars that were either fungicide-sprayed or not sprayed. Disease severity was greatest on leaves at the lowest nodes from early vegetative through the reproductive growth stages. Area under the disease progress curve (AUDPC) values and percentage of nodes defoliated at growth stage R5 were significantly (P=0.05) greater in non sprayed plots for all cultivars in both seasons. Yield losses ranged from 8 to 37% for the four cultivars. Number of pods per plant in fungicide-sprayed plots did not differ from those in non sprayed plots. However, the number of seeds per plant and seeds per pod were significantly (P=0.05) greater in sprayed than non sprayed plots for some cultivars. In experiment two, cultivar Tunia was either fungicide-sprayed at different times or not sprayed. The lowest attached leaf had the most variation in the amount of disease while ratings of the median-most leaf in the canopy were generally less variable. The AUDPC values calculated from the lowest attached leaf, the mean of all attached leaves, and the median attached leaf differed significantly (P=0.05) by the number of time plants were sprayed with fungicide. Defoliation and vertical incidence of red leaf blotch from lower to higher nodes were significantly (P=0.05) reduced in fungicide-sprayed plots in one season, but not the other. One-thousand seed weight and yield differed significantly (P=0.05) by treatment as one application of triphenyltin acetate increased yields by 18% over non sprayed plots in season one.