Breeding Open-Pollinated, Hybrid and Transgenic Outcrossing Species

Abstract

At least 50 % of crops are outcrossing species whose reproductive system includes devices promoting it. These species exhibit mild to severe inbreeding depression and significant heterosis. There are composite, hybrid, and synthetic cultivars of outcrossing species. Inbred line development, population improvement, genetic engineering, and DNA marker-aided breeding are used for the genetic enhancement of outcrossing species. Maize is an outcrossing species model system for genetics and breeding. Many of its traits are multigenic and show small effects. Maize breeding success depends on developing adapted germplasm with desired traits for various end-users. DNA markers have been used for linkage and association-based mapping, and to identify marker–trait association, but single-nucleotide polymorphisms are preferred today for maize genetic enhancement. Transgenic maize cultivars widely grown by farmers include insect resistance and herbicide tolerance alone or stacked. Cotton may have up to 30 % of outcrossing and its domesticated diploid and tetraploid species show the lint or the spinnable seed fibers that result from human selection. The crossbreeding methods for cotton include mass selection, pedigree, backcrossing, hybrids to exploit heterosis, and recurrent selection. Biotechnology led to developing transgenic cultivars, which account for 81 % of the world’s cotton acreage plantings due to their significant production gains, plus economic, environmental, health, and social benefits. Cassava is a vegetatively propagated crop whose tuberous roots are used as a main staple by many millions of people in the tropics. This root crop is an outcrossing species because of monoecy and protogyny. A sort of mass phenotypic recurrent selection is its main crossbreeding scheme. Cassava breeding may become more efficient through aid by DNA markers, while genetic engineering is a complementary approach for cassava germplasm enhancement.