Meiosis of a Triple Species Hybrid in Gossypium

Abstract

SKOVSTED^1,2 brought forward considerable cytological evidence that New World (n = 26) cottons originated by amphidiploidy from crosses between ancestral Asiatic (n = 13) and American (n = 13) parents. Recently Harland³ and Beasley⁴ have independently synthesized by colchicine treatment amphidiploids from hybrids between present-day Asiatic and American diploid species. Since the synthesized amphidiploids produce partly fertile hybrids on crossing with present-day New World types, they contribute strong supporting evidence to Skovsted's theory. It should be pointed out, however, that such evidence can only be considered critical if it can be shown that genom combinations other than Asiatic + American do not pair equally well with the New World complement. I have brought forward^5,6 phenogenetic evidence which suggests that critical examination of Skovsted's hypothesis may now be confined to testing combinations between Asiatic species and one or other of several entire-leaved species. The following combinations should be worth testing: It will be noted that all combinations except the fourth include an American diploid genom. Clearly if G. sturtii could be eliminated as a possible ancestor of New World cottons, Skovsted's hypothesis would be considerably strengthened. The low meiotic pairing found by Skovsted² in New World × G. sturtii hybrids (A C D) and the high pairing found by Beasley⁷ in the corresponding hexaploid (A C D)₂ certainly do not suggest G. sturtii as a possible parent—a conclusion which is supported by the data presented below.