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 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, 4 nucleate microspore from 1 microspore mother cell (MMC) rather than the normal 4 single-nucleate microspores from 1 MMC. Subsequent gametophyte development is characterized by fusion of the 4 nuclei into a single nucleus in most cases (range of 80-100%), followed by a developmental sequence comparable to normal alfalfa. Mature 4n male gametophytes are formed from 2n sporophytes. Genetic control of the postmeiotic cytokinesis failure is by a single recessive gene, designated ip. Although a low frequency of jumbo pollen does germinate (range of 3.1-37.8%), crossing studies demonstrate jumbo pollen is incapable of effective fertilization. The use of the ip mutant in breeding studies, and interspecific hybridization research, is discussed.