Division of Genetics, Indian Agricultural Research Institute, Delhi-12
Crosses between Gossypium arboreum (2n=26) and G. hirsutum (2n=52) give rise to viable hybrids only rarely and, in view of the economic potentialities of this cross, a clear understanding of the crossability barriers operating and of the methods of overcoming them is desirable. Detailed study has been reported of seed development in selfed arboreum and hirsutum, and in reciprocal crosses between them. The cross arboreum × hirsutum appears to faii due to some kind of physiological imbalance between the hybrid endosperm and the embryo, as the endosperm first degenerated round about the embryo. A majority of the mature seeds was empty but occasionally undifferentiated embryos were observed which never sprout, if sown directly. The cross hirsutum × arboreum failed due to the collapse of the maternal tissue, the hybrid endosperm growth being subnormal right from the beginning. Difficulties in nutrient supply perhaps affect the growth of the endosperm and cause the collapse of the integuments. Grafting prior to crossing improved the fruit setting by about 10-fold. An embryological study of the crosses grafted-arboreum × hirsutum and grafted-arboreum X grafted-hirsutum revealed that the endosperm survived upto 10 days. Later it underwent the same course of degeneration as in the normal cross. However a large number of hybrid seeds with underdeveloped embryos were obtained as a result of increased seed setting in crosses made in grafted plants The pollen from, the grafted plants did not influence the fruit setting and seed development
