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Inbreeding Cultivated Alfalfa in One Tetraploid-Haploid-Tetraploid Cycle: Effects on Morphology, Fertility, and Cytology¹

Nine haploids (2n=2x=16) from three cultivated alfalfa (Medicago saliva L.) clones (2n=4x=32) were retetraploidized using colchicine. The level of homozygosity in such retetraploidized plants is reportedly equivalent to about 3.8 generations of selfing, although they have not gone through a sexual generation. Also, they have only monoallelic and duplex diallelic loci. Tetraploid leaflet shape and serrations were restored in all cases. All other size and vigor (fresh weight) relationships and fertility were influenced by inbreeding depression, individual genes, or an interaction of these and ploidy. In general, vigor was restored to a greater degree than fertility; perhaps a reflection of selection pressure for vigor, but none for fertility, imposed on developing haploids. Factors causing low fertility were operative postmeiotically since chromosomes paired mainly as bivalents (multivalents only 0 to 0.7 per cell) and meiosis was normal in induced tetraploids. Evidence for inbreeding depression being manifested at both gametophytic and zygotic levels was discussed.

Key Words: Medicago saliva • Breeding • Polyploidy • Colchicine

² Research Assistant and Associate Professor, Department of Agronomy.

Received for publication May 25, 1972.