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Effect of Seedborne Diaporthe phaseolorum var. sojae on Germination, Emergence, and Vigor of Soybean Seedlings. M. M. Kulik, Plant pathologist, Seed Research Laboratory, Agricultural Research, Science and Education Administration, Beltsville, MD 20705; J. F. Schoen, plant pathologist, Seed Standardization Branch, Agricultural Marketing Service, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 71:544-547. Accepted for publication 4 November 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-71-544.

A total of 244 soybean (Glycine max) seed lots were assayed over a 3-yr period for infection by Diaporthe phaseolorum var. sojae (DPS) by using an agar health test, and for germination, vigor, and emergence in laboratory and greenhouse tests. Field emergence was recorded at several locations. Simple correlation coefficients were computed between the incidence of DPS and measurements of germination, vigor, and greenhouse and field emergence. Correlations between DPS and germination or vigor in the official towel test and the modified towel test were often negative and highly significant (P = 0.01). Correlations between DPS and nearly all of the results of the accelerated aging test and between most of the measurements from the sand bench and cold tests were not significant. The correlations between DPS and field emergence were sometimes negative and highly significant but were of lower magnitude than in the germination and vigor tests. Results indicate a definite inverse relationship between infection of soybean seeds by DPS and their germination, vigor, and field emergence. Also, the need for large-scale comprehensive studies to assess the effects of infection by seedborne pathogens on seed quality and seedling performance was confirmed. Of the tests used in this study, the official towel test and the modified towel test were the best for determining the effect of seedborne DPS on soybean seed quality. We suggest that the former be used for this purpose because it is simpler than the latter.