Advances in Hybrid Breeding Methodology

Abstract

Hybrid cultivars are the first generation (F1) progeny of a cross between two or more selected and genetically diverse parents, and these exploit heterosis. Heterosis is defined as increased vigour, size, fruitfulness, speed of development, resistance to disease and insect-pests or to climatic rigours of any kind in F1 generation. Dominance of linked loci, over dominance, and epistatic gene action were proposed to explain the genetic basis of heterosis. Logically all types of gene action controlling the inheritance of a trait should be expected to contribute to heterosis. Hybrid breeding started in maize, and experiences in this crop have greatly contributed to the development of hybrid breeding methodology which is continuously evolving and expanding. In sorghum, pearl millet, sunflower etc., hybrid breeding started with the development of male sterility and fertility restoration system for pollination control. The technology was largely confined to cross-pollinated crops with a few exceptions like tomato and cotton. In the late 1970s, the success of hybrid rice, a strictly self-pollinated crop in China provided an impetus to hybrid breeding. The possibility to use environment-sensitive genetic male sterility and chemical hybridizing agents has opened the avenue of widening the base of parental germplasm and enhancing the magnitude of heterosis; and it is likely to simplify hybrid breeding and seed production. Further, the use of recurrent selection to develop hybrid breeding oriented source germplasm needs greater emphasis. The application of biotechnological techniques such as doubled haploidy, somatic hybridization, analysis of molecular diversity and marker assisted selection are expected to provide cutting edge to hybrid breeding; for which biotechnology needs to be integrated with hybrid breeding. Another exciting area is the development of apomictic hybrid that should greatly expand the coverage by hybrid cultivars.