Faculty Publications and Research, Page 32-33 (1957)
North Carolina State University. Graduate School

WEAVER, JAMES BODE, JR. A Study of Embryo Abortion in Reciprocal Inter-Specific Crosses of Gossypium (under the direction of DAN ULRICH GERSTAL).

Crosses were made between Asiatic diploids, American cultivated tetraploids and synthetic hexaploids and a few other species.

Certain general observations could be made: When the female parent had the lower chromosome number the endosperm and maternal tissue made a rapid initial growth but the endosperm became abnormal about 5-7 days after pollination. The endosperm showed irregular mitotic divisions, dumb-bell-shaped nuclei, and nuclei of abnormal size. The endosperm completely degenerated 2-3 weeks after pollination without ever forming cell walls. The embryo grew at a normal rate for the first 10-12 days after pollination but then growth lagged. Over 200 excised embryos from the low-chromosome X high-chromosome cross were placed on culture medium but all except three failed to become properly differentiated.

In the reciprocal crosses, that is, high chromosome females X low chromosome males, the development was entirely different. In 4n X 2n and 6n X 2n crosses only a small amount of endosperm, embryo or maternal tissue growth occurred. The endosperm growth ceased about 5-6 days after pollination and became cellular 2-4 days earlier than normal. In 4n X 2n crosses there was a competition or possibly inhibitory interaction between the embryo and the endosperm. The embryo and endosperm in this type of cross were unable to make normal growth within the same ovule, but when triple fusion occurred without fertilization of the egg cell the hybrid endosperm developed in a normal manner, producing a large embryo-less ovule. An exception among the high X low crosses was found in the 6n X 4n crosses which frequently gave viable seeds.

Other exceptions to the above generalizations include certain incompatible 2n X 2n crosses which behaved the same as low X high chromosome crosses, and one 4n X 2n combination which developed normally.

After pollination of 4n plants with a mixture of Asiatic (2n) and self pollen, it was found that culturable hybrid embryos were located near the selfed seeds in the locule. It was concluded that a stimulus produced by the endosperm of the selfed ovules influenced the growth and differentiation of the hybrid embryos. Embryo-less ovules had the same effect upon adjacent hybrid embryos. However, in 2n X 4n mixed pollinations selfed seeds had no influence upon the hybrid embryos.

Considerable variation was found in the behavior of different strains of G. hirsutum (4n) as female parent in mixed pollinations with G. arboreum (2n). Three types of reactions were observed. 1) Hybrids could not be obtained, 2) very small hybrids were produced that would survive only on culture medium, 3) viable hybrid seeds of normal size were formed.

The possibility of heterofertilization playing a role in natural interspecific hybridization is discussed. One condition necessary for heterofertilization to occur in cotton was shown by the occurrence of two pollen tubes within the same embryo sac.

Weaver Jr., J. B.: A study of embryo abortion in reciprocal interspecific crosses of Gossypium. Doct. dissert., North Carolina State College, Raleigh 1955.

Weaver, James B. Embryological Studies Following Interspecific Crosses in Gossypium. I. G. Hirsutum x G. Arboreum. American Journal of Botany 44(3): 209-214 (1957)

Weaver, James B. Embryological Studies Following Interspecific Crosses in Gossypium. II. G. Arboreum X G. Hirsutum. American Journal of Botany 45(1): 1-16 (1958)

Cotton Bibliography

Heterofertilization Bibliography

Pollen Mixtures Bibliography

Vysotskii: Wide Hybridization in the Malvaceae [cotton] (1960)