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Inheritance of Density of Erect Glandular Trichomes in the Genus Medicago¹

The successful development of an interspecific, erect glandular-haired, tetraploid population of alfalfa, involving Medicago sativa L.; M. prostrata Jacquin; and M. falcata glandulosa David, with an adequate density of hairs for resistance to several insect pests is described. The objective of this study was to determine magnitudes of genetic and nongenetic variance components, repeatability, and heritability of glandular-hair density in this population. A random sample of 40 genotypes from this population was randomly intermated. Twenty-two genotypes and their progeny were measured for density of glandular hairs in a randomized complete-block design with two blocks. Parental plots consisted of eight vegetatively propagated plants of each parental clone, and the progeny plots included 16 random-intercross individuals from each parent as a female. The third fully elongated internode from the apex on two stems per plant was measured for number of glandular hairs per square millimeter (g.h. mm^–2). The design variance components of parental clones were estimated. The phenotypic variance was partitioned into additive (29%), nonadditive (16%), general environmental (29%), and special environmental (26%) variances. A repeatability of 0.74 was obtained and used to compute the gain in accuracy to be expected from repeated measurements. The gain was substantial with two measurements per plant, but the extra time and effort required to obtain more than two measurements would be generally unwarranted. Parent-offspring regression analysis gave an estimate of 0.55 for the narrow-sense heritability. The predicted gain in number of g.h. mm^–2, obtained by selecting the upper 10% of the parent plants and recombining them, was 1.76 g.h. mm^–2. This gain represented 45% of the parental population mean.

Key Words: Medicago sativa L. • Medicago prostrata Jacquin • Medicago falcata glandulosa David • Repeatability • General environmental variance • Special environmental variance • Predicted selection gain

² Research associate, assistant professor of entomology, and professors of agronomy, Purdue Univ., W. Lafayette, IN47907, respectively.

Received for publication June 25, 1984.