ABSTRACT
Transfer of useful genes to crop species from other accessions or species through hybridization has been the most effective approach in crop improvement programmes for many decades. Broadening the genetic base of cultivated species is an essential prebreeding requirement to maintain stability and further improve yield. A large number of accessions of related species and often wild species of cultivars have to be screened to identify those with desirable genes before they can be transferred to the cultivated species. Use of pollen for screening for desirable genes is dependent on the expression of the required gene(s) in the pollen grain. Strong crossability barriers between parents which may operate before and/or after fertilization are the major constraints in any hybridization programme. The most important physical barrier for wide hybridization is non-synchronous flowering or geographic isolation of the parent species.
