Creation of Heterotic Groups and Hybrid Varieties

Abstract

Capturing heterosis for dry matter yield in forage crops needs to consider both the final product of the breeding process (the type of cultivar) and the breeding method used to produce the cultivar. The discussion is focused specifically on alfalfa and on the semi-hybrid variety model allowing partial expression of heterosis with the technology currently in use and no drawbacks to seed production. The search for heterotic groups is a key point to improve the process of semi-hybrid construction. Among-subspecies diversity (i.e., Medicago sativa subsp. sativa and falcata) and selfing within subspecies are reviewed as tools to manage genetic diversity and to test the value of gene and linkat interactions in crosses. Different breeding methods have been proposed to produce semi-hybrid varieties. Experimental results on heterosis expression and yield gain of semi-hybrids vs the corresponding synthetic variety or elite cultivar are discussed in pointing out the basis of heterotic performance and in defining what are the key points in method and selection procedures to effectively exploit heterosis.