Wild taxa are invaluable sources of resistance to diseases, insects/
pests, nematodes, temperature extremes, salinity and alkalinity
stresses, and also of nutritional quality; adaptation; genetic diversity
and new species. Utilization of wild relatives of a crop depends largely
upon its crossability relations with cultivated varieties. Sev- eral
wild species are not crossable with the commercial cultivars due to
various isolation barriers. Furthermore, in a few cases, hybridiza- tion
is possible only in one direction and reciprocal crosses are not
successful, thus depriving the utilization of desired cytoplasm of many
species. However, techniques have been developed to over- come many
barriers and hybrid plants are produced. New crop species have been
developed by overcoming the F 1 sterility and producing amphidiploids
and such crops are commercially being grown in the field. The
segregation pattern ofF 1 hybrids produced by distant hybridization in
segregating generations are different from the intervarietal hybrids. In
former cases, generally, unidirectional segregation takes place in early
generations and accordingly, selec- tion procedures are adopted. In most
of the cases, backcross or modified backcross methods have been followed
to utilize wild species, and thus numerous types of resistance and other
economical attributes have been transferred in the recurrent parents.
Protoplast fusion has been amply demonstrated in a number of cases where
sexual hybridization was not possible and, as a result, hybrids have
been produced.