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UBC Theses and Dissertations

Breeding behavior in interspecific hybrids (Medicago falcata x M. sativa), parent stock of Rhizoma alfalfa Nilan, Robert A.

Abstract

Rhizoma, a new alfalfa variety possessing a distinctive spreading habit, was developed from six hybrids of a cross between the species Medicago falcata var. Don (seed parent) and Medicago sativa var. Grimm or Ontario Variegated (pollen parent). Because of its unusual origin, it differs from other alfalfa varieties grown in North America, Cytological investigations showed the falcata parent to be a low chromosome alfalfa (S = 16) and the sativa parent to be high chromosome alfalfa (S = 32). Three of the six hybrids were triploids (S = 24) and three were tetraploids (S = 32), the latter having received sixteen chromosomes from the female parent, possibly through the formation of unreduced gametes. It was concluded that the new variety Rhizoma is a permanent tetraploid hybrid (S = 32) containing an equal complement of chromosomes from each parent. Pollination and fertility studies on selected clonal lines of the F₄ generation revealed that a considerable amount of seed set under open-pollination was selfed seed and that much of the seed was being set without the aid of bees. The combining ability of the lines varied considerably and it was concluded that the effectiveness of each line as a male and female parent must be determined for a true criterion of combining ability. In addition, it was found that, in contrast to other varieties, the seed set after controlled cross-pollination did not greatly exceed the seed set after self-pollination.

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