REDUCING THE TETRAPLOID NONNODULATING ALFALFA (MEDICAGO-SATIVA) MNNC-1008(NN) GERM PLASM TO THE DIPLOID

MnNC-1008(NN) (referred to as MN-1008) is a tetraploid alfalfa mutant with two recessive genes (nn(1) and nn(2)) conditioning the non-nodula ting trait. The tetraploid level (2n=4x=32) of this Medicago sativa ge rm plasm was reduced to the diploid (2n=2x=16) level using the 4x-2x g enetic cross originally described as a workable method for the inducti on of haploidy in alfalfa by T. E. Bingham. In our experiments more th an 7000 emasculated flowers of a single non-nodulating MN-1008 mutant alfalfa plant with purple petals were cross-pollinated with pollen fro m a single, diploid, yellow-flowered alfalfa plant. Mature seeds from these crosses were collected and germinated, after which the plants we re subjected to morphological and cytogenetic analyses as well as to D NA fingerprinting. Out of 26 viable progeny, 6 were hybrid plants, 19 proved to be self-mated derivatives of MN-1008, while one descendant t urned out to be a diploid (2n=2x=16), purple flowered, non-nodulating plant denoted as M. sativa DN-1008. This diploid, non-nodulating alfal fa plant can serve as starting material to facilitate the comprehensiv e morphological, physiological and genetic analysis (gene mapping and cloning) of nodulation in order to learn more about the biology of the symbiotic root nodule development. To produce diploid; nodulating hyb rid F-1 plants, DN-1008 was crossed with a diploid, yellow-flowered M. sativa ssp. quasifalcata plant. An F-1 population segregating the nn( 1) and nn(2) genes in a diploid manner, in which the genetic analysis is more simple than in a tetraploid population, can be established by self-mating of the F-1 plants.