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Disease Detection and Losses

Use of Near-Isogenic Host Populations to Estimate the Effect of Three Foliage Diseases on Pearl Millet Forage Yield. Glenn W. Burton, Research geneticist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and the University of Georgia, College of Agriculture Experiment Stations, Coastal Plain Station, Tifton 31794; H. D. Wells, plant pathologist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and the University of Georgia, College of Agriculture Experiment Stations, Coastal Plain Station, Tifton 31794. Phytopathology 71:331-333. Accepted for publication 25 July 1980. 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, 1981. DOI: 10.1094/Phyto-71-331.

Forage yields of F2 and F3 near-isogenic populations of pearl millet, Pennisetum americanum, were used to estimate the effect of Cercospora leaf spot (caused by Cercospora penniseti) red leaf spot, and brown leaf mottle (the latter two of unknown etiology). Pearl millet inbreds used to create the populations were: Tift 18 (susceptible to brown mottle); Tift 13 (resistant to brown mottle); 442 (susceptible to red spot and resistant to C. penniseti); and 664 (resistant to red spot and susceptible C. penniseti). The F2 near-isogenic populations of varying degrees of resistance were established based on disease data collected from about 1,000 spaced F2 plants of a cross between resistant and susceptible inbreds. Mean yields of plants in five disease severity classes were compared to determine the effect of Cercospora leaf spot on yield. The F3 near-isogenic populations were prepared by mixing equal quantities of selfed seed from F2 plants (of a resistant susceptible cross) having the same F2 disease classification. These seed mixtures were planted in a replicated small plot trial in which three forage yields were taken. Both procedures for establishing near-isogenic populations require the grouping of enough F2 plants or selfed seed to create populations with similar frequencies for all genes affecting yield except the genes controlling the disease and those closely linked to them. The F2 near-isogenic population tests showed that red spot had no effect on forage yield, whereas Cercospora leaf spot, when severe, reduced forage yields 2025%. In the F3 near-isogenic population test, brown mottle had no effect on the first forage yield, but reduced the second harvest by 23% and the third harvest by 30%. Thus, red spot susceptibility or resistance may become a useful genetic marker, whereas Cercospora leaf spot and brown mottle are diseases that should be controlled by the breeding of resistant lines.