Genetics, cytology, and crossing behavior of an alfalfa (Medicago sativa) mutant resulting in failure of the postmeiotic cytokinesis

Abstract

During pollen investigations on diploid alfalfa (Medicago sativa L.) several plants were identified which produced "jumbo" pollen. The cause of the jumbo pollen is failure of the postmeiotic cytokinesis. These plants produce a single, four-nucleate microspore from one microspore mother cell (MMC) rather than the normal four, single-nucleate microspores from one MMC. Subsequent gametophyte development is characterized by fusion of the four nuclei into a single nucleus in most cases (range of 80 to 100%), followed by a developmental sequence comparable to normal alfalfa. Mature 4n male gametophytes are thus formed from 2n sporophytes. Genetic control of the postmeiotic cytokinesis failure is by a single recessive gene, designated jp. Although a low frequency of jumbo pollen does germinate (range of 3.1 to 37.8%), crossing studies demonstrate jumbo pollen is incapable of effecting fertilization. The use of the jp mutant in breeding studies, and interspecific hybridization research, is discussed.