Apomixis in crop improvement

Abstract

Apomixis is a method of asexual reproduction in plants with three main variants, viz., apospory, diplospory, and adventitious embryony. Genetic understanding of apomixis has been handicapped for a long time due to lack of techniques for a rapid and accurate identification of apomictic and normal plants. Subsequent development of techniques for isolation of embryo sacs, use of flow cytometry, and availability of molecular markers facilitated an early identification of apomictic genotypes. Apomixis is now considered to be a consequence of deregulation of the genes involved in sexual reproduction. Though the inheritance of apomixis appears to follow Mendelian principles, every conceivable complication for genetic analysis such as epistatic gene interactions, components that are expressed sporophytically and gametophytically, expression modifiers, polyploidy, segregation distortion, and suppressed recombination is now thought to have accumulated in apomicts. Biotechnological work carried out on some plant systems— Pennisetum, Brachiaria, and Paspalum —where apomixis has been subjected to detailed molecular genetic analysis is summarized here because of the importance of concepts and experimental strategies involved. The three features of apomixis, viz., (1) ease of multiplying and maintaining elite hybrid genotypes, (2) ease of producing high-quality pure seed without isolation requirements, and (3) possibility for selection of a diversity of more closely adapted genotypes, are expected to provide means for indefinite fixation of hybrid vigor and lower the cost of hybrid seed production. Though significant advancement has taken place in our understanding and handling of apomixis, no gene has yet been isolated that could convincingly be labeled as “apomixis gene.” Nevertheless, attempts made so far have led to the optimism that apomixis can be available to the breeder in a not too distant future.