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Yields of Alfalfa Varieties Selected for Aphanomyces Resistance in Kentucky

Dep. of Plant Pathology, Univ. of Kentucky, Lexington, KY 40546-0091.

Leonard M. Lauriault and Jimmy C. Henning

Dep. of Agronomy, Univ. of Kentucky, Lexington, KY 40546-0091.

^* Corresponding author (Email: pvincell{at}ca.uky.edu).

Field tests were conducted over 4 yr to investigate whether alfalfa (Medicago sativa L.) varieties and experimental populations selected for resistance to aphanomyces root rot (caused by Aphanomyces euteiches Drechsler) (here termed aphanomyces-selected varieties) would collectively outyield varieties not selected for resistance (unselected varieties). All entries were resistant to phytophthora root rot (caused by Phytophthora medicaginis E.M. Hans & Maxwell). At the conclusion of the tests, the mean cumulative dry matter yield of aphanomyces-selected varieties was higher (4.2% increase, P = 0.063) than that of unselected varieties in a site naturally infested with A. euteiches and P. medicaginis. However, total yields of certain unselected varieties equaled or even exceeded (P = 0.10) those of certain aphanomyces-selected varieties, and there was no correlation among varieties between yield and percentage of Aphanomyces-resistant plants. No significant difference in mean cumulative yield was observed between aphanomyces-selected and unselected varieties in two sites infested with A. euteiches alone nor in four sites not infested with either pathogen. Since outbreaks of seedling diseases were minor in all tests, the yield effects observed may be due to differences in plant health manifested after stand establishment. Our data are consistent with the hypothesis that selection for Aphanomyces resistance contributes to an overall improvement of elite alfalfa germplasm for cultivation in poorly drained soils infested with both A. euteiches and P. medicaginis. However, considered alone, selection for Aphanomyces resistance in individual varieties was not always predictive of high yield in Aphanomyces-infested sites. These tests do not rule out the possibility of a substantial yield benefit to Aphanomyces resistance under conditions unusually conducive to seedling disease induced by A. euteiches.

Received for publication May 23, 1994.

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				P. Vincelli, J. Henning, T. Hendrick, J. Brown, L. J. Osborne, B. Prewitt, V. Shields, D. Sorrell, K. D. Strohmeier, R. Tackett, et al. Improved Seedling Health, Yield, and Stand Persistence with Alfalfa Resistant to Aphanomyces Root Rot Agron. J., November 1, 2000; 92(6): 1071 - 1076. [Abstract] [Full Text]