Interspecific Hybrid Sterility Research Articles

Hexaploid Cotton: Some Plant and Fiber Properties 1

Hexaploid cottons were made by crossing Gossypium hirsutum L. (Acala 44-10-1) and Gossypium sturtianum Willis. The chromosome number of the sterile interspecific hybrids was doubled with colchicine. The hexaploids were selected and grown for several years. Fiber and spinning data were collected for the first time from plants having more than 52 chromosomes. The hexaploid cotton fibers produced yarn with very high yarn strength.

Interspecific Hybridization in Trifolium1

The interspecific relationships among several Trifolium spp. in the section Calycomorphum were studied. Crosses involving T. israeliticum, T. globosum, and T. pauciflorum failed to produce hybrid seed. Crosses among T. subterraneum, T. eriosphaerum, and T. pilulare gave varying results. Complete interspecific sterility was most common; however, 3 F1 plants (1 plant from the T. eriosphaerum ✕ T. subterraneum cross and 2 plants from the T. pilulare ✕ T. subterraneum cross) survived till after flowering. The F1 plants had morphological characteristics of both parents. F2 seeds were formed, probably through backcrossing, in two male sterile interspecific hybrids, T. subterraneum ✕ T. eriosphaerum and T. pilulare ✕ T. subterraneum. Fertility was partially restored in the F3 and F4 lines, although several fertile F3 plants produced sterile progenies. The results suggest that this group is young and shares common morphogenetical and physiological systems because interspecific hybrids can be obtained by conventional methods. Morphological specialization is more advanced than the reproduction barriers because the taxa involved are self‐fertilized annuals and are isolated spatially.

The Inviability, Weakness, and Sterility of Interspecific Hybrids

In this chapter, the review of available data clearly points to the conclusion that the causes underlying the erection of barriers of reproductive isolation, therefore of the origin of species, differ considerably from one group of organisms to another. Furthermore, these differences are related to other differences among groups of organisms, such as size and structure of populations, rates of reproduction, and methods of adaptation. In the future, therefore, the study of the origin of species should not be a search for any more general causes, which might be considered as responsible for speciation in all groups of organisms, but a series of special and comparative investigations, by means of which the interrelationships mentioned above, as well as others as yet unknown, can be further explored and more firmly established.