It is very difficult to produce hybrids in case of interspecific and inter-generic crosses (crosses between distantly related plants), because abnormal development of the endosperm causes the premature death of the hybrid embryo and leads to sterile seeds. The embryo from such sterile hybrid seeds can be excised at an appropriate time and cultured on a suitable nutrient medium to produce novel hybrids which are otherwise not possible. This is known as Embryo Rescue. Several useful hybrids were produced in a variety of crops using this technique.
