Tetrasomic Segregation for Multiple Alleles in Alfalfa1

Evidence of tetrasomic inheritance in alfalfa, Medicago sativa L. and M . falcata L., for multiple codominant alleles at three isozymic loci is reported in this study. The locus Prx-I governing anodal peroxidase and the loci Lap-I and L a p 2 governing anodal leucine-aminopeptidase were studied by starch gel electrophoresis in seedling root tissue or seeds. The progenies from several di-, trior tetra-allelic plants belong to the species M. sativa and M . falcata and their hybrids were studied for the segregation of the three genes. In all cases, tetrasomic inheritance of chromosomal-type segregation was observed. In another progeny resulting from the crossing of two plants involving four different alleles at locus Lap-2, tetrasomic segregation with the possible occurrence of double reduction was observed. This study presents direct evidence of autotetraploidy and the existence of tetra-allelic loci in alfalfa. I t also supports the concept that the species M . sativa and M. falcata are genetically close enough to be considered biotypes of a common species. M O S T of the information dealing with the biochemical genetics of polyploids has been obtained from allopolyploid species. ROOSE and GOTTLIEB (1976) have provided a good review of this field. In their study of Tragopogon they discuss the fitness advantages of this type of polyploid, due perhaps to fixed heterozygosity, which is likely to result in increased biochemical versatility. For autotetraploids there is much indirect evidence on the tetrasomy and the possible origin of these species (HARLAN and DEWET 1975). For instance, in several species of fish, evidence of autotetraploidy is based on gene duplication, chromosome number, relative DNA value and residual tetrasomy (WRIGHT et al. 1980). In plants, evidence of autopolyploidy has been obtained mostly on the basis of segregation ratios for morphological characteristics and chromosome pairing. Alfalfa (Medimgo sativa L. and M . falcata L.) is considered to be an autotetraploid (2n = 4.x = 32) (BARNES and HANSON 1967; BUSBICE, HILL and CARNAHAN 1972; BARNES et a2. 1977; BINGHAM 1979). STANFORD (1951) presented the best documented evidence of autotetraploidy in this crop after demonstrating tetrasomic segregation for flower color in F, generations. The availability of electrophoretic markers in alfalfa representing various loci wtih multiple alleles (QUIROS and MORGAN 1981) provides a better insight into the genetic structure of this crop. This is facilitated by having both diploid and tetraploid 1 This paper i s dedicated to Profess9r C H ~ R L E S >!I R i c e in the gear of his rellrement 2 Present address Internatlonal Plant Re>earch Instltute, 853 Industrial Rd San Carlos, Callfomla 94070, U.S A. Genetics 101: 117-127 hIay, 1982