Semigamy Gene Is Associated with Chlorophyll Reduction in Cotton
2004
Zhang, J. F. | Stewart, J. McD.
Haploids produced by semigamy can be used to facilitate selection in cotton (Gossypium barbadense L.) breeding and gene mapping. The objectives of the present study were to detail the genetic mechanism of semigamy and its relationship with reduction in chlorophyll content. Pima 57-4, a semigametic line isolated as a doubled haploid (DH) from Pima S-1, produced 46 to 50% haploid progeny when selfed. Compared with its natural isogenic line S-1, 57-4 had lower leaf chlorophyll content, photosynthetic rate (Pn), and boll weight, and had higher lint percentage, seed index, and shorter and coarser fiber. Three segregating populations (F₂ and two BC₁F₁) from a cross of 57-4 × S-1 were progeny tested to investigate the genetic basis of semigamy. Haploid production in F₁, F₂, and backcrosses were also recorded. The results verified that semigamy in cotton is controlled by one gene, previously designated Se The gene functions sporophytically and gametophytically, resulting in incomplete dominance nature. A generation-mean analysis for the cross of 57-4 × S-1 identified one gene responsible for the parental differences in chlorophyll content. Consistent with the difference between the two parental isogenic lines, semigametic F₂.₃ lines had significantly lower chlorophyll content than nonsemigametic F₂.₃ lines, an observation that was confirmed by a significant association between haploid production and chlorophyll content. The Se gene and the gene for reduced chlorophyll content could be either the same or closely linked. The elucidation of the relationship between semigamy and fiber development will help characterize the molecular function of the semigametic gene.
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