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Gametophytic Heterosis for In Vitro Pollen Traits in Alfalfa

Dep. of Plant, Soil and Insect Sciences, Univ. of Wyoming, Laramie, WY 82071-3354
Dep. of Agronomy, Univ. of Wisconsin-Madison, Madison, WI 53706.

^* Corresponding author.

Heterosis may occur in gametophytes of polyploid sporophytes. for genes expressed in the diploid pollen (n = 2x) of autotetraploid plants (2n = 4x), favorable dominance, overdominance, and increased epistatic interactions are possible and could result in heterosis for microgametophytic traits. Pollen competition could function to maintain high levels of heterozygosity in autotetraploid populations if highly heterozygous pollen is more competitive for ovules. The objectives of this study were to evaluate heterosis for microgametophytic traits and to compare performance of microgametophytic and important sporophytic traits in autotetraploid (2n = 4x = 32) alfalfa (Medicago sativa L.) using populations bred to be isogenic (same alleles and allele frequencies) but to differ in levels of heterozygosity. In vitro, more higly heterozygous pollen was more germinable and produced longer pollen tubes, indicating gametophytic heterosis. Numerouos positive correlations between microgametophytic and sporophytic traits were observed in these populations.

Received for publication October 17, 1990.