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Published in Crop Sci 19:253-257 (1979)
© 1979 Crop Science Society of America
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Allocation of Resources in Selection for Resistance to Alfalfa Blotch Leafminer in Alfalfa1

R. R. Hill, Jr. and R. A. Byers2

Sixteen plants from each of 54 polycross families of alfalfa (Medicago sativa L.) were evaluated for reaction to the alfalfa blotch leafminer (Agromyza frontella Ron-dani). Reaction to the insect was measured as the number of mined leaflets in a 30-leaflet sample taken from each plant on first harvest and later-season forage in 1976 and 1977. Estimates of variance components were used to calculate heritability of resistance and estimated gain from mass, half-sib family, and modified ear-to-row selection. Predicted gains were compared to determine optimum allocation of number of replications and selection pressures to apply within and among families.

Variability among families was significant, but the heritability estimate was low (4.18%). Predicted gains with modified ear-to-row selection were greater than with mass selection only if the number of replications was large and the selection intensity within families was moderate. Half-sib family selection always had smaller predicted gains than the most effective modified ear-torow procedure. Mass selection had greater predicted gains when the number of replications was low and selection intensity within families was very low or very high. The predicted efficiency of mass selection increased relative to that of the other methods when the overall selection intensity decreased. The modified ear-to-row procedure with high selection intensity was recommended for increasing resistance to the leafminer alfalfa.

Key Words: Medicago sativa L. • Agromyza frontella Rondani • Selection methods

1 Contribution No. 467 from the U.S. Regional Pasture Res. Lab., AR, SEA, USDA, University Park, PA 16802.

2 Research agronomist and research entomologist, respectively.

Received for publication September 9, 1978.




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