Viable hybrids are produced as a result of sexual crosses between two varieties of the species. However, if sexual crosses are done between the species of the same genus or between two different genera, production of hybrid is rather difficult because of several barriers arising either during pollination, fertilization or embryogenesis. It has been observed that in some cases in spite of successful pollination and fertilization, embryo does not develop. This is due to inherent deficiencies or incompatibility between the developing embryo or endosperms. In such cases, immature embryos are dissected out from the fruit (seed) and grown artificially on medium which differentiate into shoot, root and plantlets. This technique of growing immature embryo is termed as 'embryo rescue'.
Embryo rescue technique is very useful in wide hybridization, complete growth of embryo in plant, breaking dormancy of certain seeds where dormancy period is very long. By using embryo rescue technique wild varieties can be crossed with cultivars. As compared with cultivars, the wild species have greater resistance to pests and pathogens, and produce grains of better quality. At the International Crop Research Institute for Semi Arid Tropics (ICRISAT), Hyderabad, this technique has been used to improve groundnut, pigeon pea and chick-pea. A new hybrid variety of pigeon-pea (ICPH8) has been developed at ICRISAT that matures in 100 days instead of 200 days. This variety is resistant to pathogens and pests and yields 20% higher than original cultivars. However, it can grow in a wide range of conditions.