Complementary Gene Interactions in Alfalfa are Greater in Autotetraploids than Diploids

Abstract

Greater complementary gene interaction in autotetraploid alfalfa (Medicago sativa L., 2n = 4x = 32) may explain differences in vigor and breeding behavior between diploids and autotetraploids. Complementary gene interaction is nonallelic gene interaction or epistasis where dominant alleles at heterozygous loci may complement each other by masking recessive alleles at respective loci. This paper describes how tetrasomic segregations of linkage blocks in linkage disequilibrium produce tetraploid individuals and populations with greater complementary gene interaction than is possible at the diploid level. This finding helps explain autotetraploid superiority and unique breeding behavior. Research on gene action in autotetraploid alfalfa has demonstrated that favorable alleles in linkage blocks underpin population improvement and increased heterosis. The individual favorable alleles with additive effects also contribute to non‐additive complementary gene interactions in linkage blocks. Apparent multiple allelic interaction (overdominance) effects discussed in earlier studies inbreeding depression and progressive heterosis in alfalfa are due mainly to linkage disequilibrium, which agrees with findings in maize. The severe inbreeding depression in autotetraploids is due mainly to the rapid loss of complementary gene interactions in the first few generations of inbreeding. Correspondingly, the progressive heterosis of autotetraploids is due mainly to a progressive increase in complementary gene interactions. Greater complementary gene interactions in tetraploid alfalfa also helps explain recent DNA research indicating that yield in tetraploids is more responsive to genetic diversity than in diploids. Many differences between diploid and autotetraploid alfalfa reported in earlier studies now may be explained by inherent differences in the levels of complementary gene interactions.

Karyotype analysis ofAstragalus effususBunge (Fabaceae)

“…This has been reported in cultivated plants such as alfalfa (BARCACCIA et al 2003), white clover (HUSSAIN and WILLIAMS 1997), and red clover SMITH 1984, 1986;PARROTT et al 1985), among others. On the other hand, these species had forage uses and therefore, polyploidy could exist in nature with adaptive advantages of lushness and largeness, and high biomass yield (BINGHAM et al 1994). For this reason, somatic polyploidization (TAY-LOR et al 1976) or sexual polyploids (RAMANNA and JACOBSEN 2003) are important tools in forage plant breeding.…”

Microsatellite Analysis of Genetic Variation and Population Genetic Differentiation in Autotetraploid and Diploid Rice

“…Further improvement in yield is difficult with diploid breeding, however, because of the small genome, DNA, and chromosome size. Experience with other crops, such as wheat and rye, indicates that plant polyploidy existed in nature with adaptive advantages of lushness, largeness, and high biomass yield, which could be used to improve the crop yield (Bingham et al 1994).…”

Breeding lucerne for persistence

“…This trend of using large numbers of parents began in the early 1970s and was based on the theoretical considerations of alfalfa's autotetraploid genetics indicating inbreeding was reduced by large parental numbers via achievement of maximum heterozygosity for intra-allelic interactions (Busbice and Wilsie 1966;Hill 1987). A reduction of complementary gene interactions rather than intra-allelic interactions was later proposed to be responsible for inbreeding depression in alfalfa (Bingham et al 1994).…”