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Self-Incompatibility in Two Alfalfa Populations

USDA-ARS, Plant Sciences Inst., Soybean and Alfalfa Res. Lab., Beltsville, MD 20705

^* Corresponding author.

Self-incompatibility provides a useful mechanism for pollination control in alfalfa, Medicago sativa L. Five hundred randomly selected seedlings from each of two well-adapted multiple pest-resistant alfalfa populations (W10 AC3 and BMP8 AC3) were screened for self-incompatibility. Twenty-eight plants were selected following three evaluations in the greenhouse. Unemasculated hand pollinations of the self-incompatible plants, using plants with the singlegene, completely dominant red-root character as the pollen source, resulted in the production of 98.6% hybrid seed. Plants were intercrossed in the greenhouse using honey bees, Apis melifera L. Growth chamber forage-yield trials of half-sib progenies indicate that certain combinations of self-incompatible plants exist that will yield significantly better than the parent populations. Twelve elite self-incompatible plants selected after the initial screening produced (i) < 0.15 seeds floret^–1 when self pollinated, (ii) =30% viable pollen, and (iii) =3 seeds floret^–1 when used as the male or female in crosses with other plants. Pollen-pistil interaction studies of the self-incompatible plants showed that the pollen had normal viability and either failed to germinate upon self pollination or pollen tube growth was abnormal. Pollen tubes that grew near the ovules either formed bulbous structures and terminated, or formed several branches, or continued to grow past all of the ovules resulting in the failure of fertilization. However, normal fertilization and good seed set were obtained when the self-incompatible plants were used both as male and female in crosses with other plants. The 12 elite self-incompatible plants were shown to have the capacity to produce somatic embryos in vitro, indicating that these plants could be propagated utilizing artificial seed technology. Evidence to date indicates that the use of the self-incompatibility system may provide a mechanism for successfully producing high-yielding hybrid alfalfa cultivars.

Received for publication August 4, 1989.