| Abstract
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A trispecific F2 mapping population was developed by crossing G. arboreum (A2) cv. Nanking with G. trilobum (D8). The diploid hybrid was treated with colchicine to produce a synthetic allotetraploid 2(A2D8). This hybrid was crossed with G. hirsutum (AD1) cv. T-586, and the resulting hybrid was self-pollinated to obtain the segregating F2 population. A total of 426 markers (332 AFLPs, 91 RAPDs and 3 morphological markers) were scored among 90 F2 plants. Fifty-seven percent of the markers showed distorted segregation, perhaps due to divergence of the three-genome species associated with chromosomal rearrangements and areas of low recombination among the genomes. A linkage map was constructed comprising 51 linkage groups that spanned 6663 cM of the cotton genome with an average distance of 18 cM between markers. Higher levels of polymorphism were observed in the D genome compared to the A genome, thus the diploid D genome appears more divergent from its alloploid Dh subgenome than A is from the Ah subgenome. Three morphological markers, pilose (T1), red plant color (R1) and naked seed (N1), that are located on chromosome 6, 16 and 12, respectively, of the cotton classical genetic map, were found to be linked with molecular markers on three different linkage groups. These markers could be useful for marker assisted selection in cotton breeding program. Terpenoid aldehydes (TAs) accumulate in the lysigenous glands of Gossypium L. (cotton genus) and related genera, and are toxic to many insect pests. Qualitative and quantitative foliar analyses for seven TAs were performed on Thespesia thespesioides (Brown ex Benth.) Fryxell and on 40 Gossypium genotypes comprising 30 species, using high performance liquid chromatography. Gossypium mustelinum Miers ex Watt had the highest leaf concentration of the heliocides H and H4, and total TAs, while heliocides H2 and H3, and hemigossypolone were highest in G. capitisviridis Mauer, G. lobatum Gentry, and G. nobile Fryxell, Craven & Stewart, respectively. Gossypol was highest in T. rhespesioides and a G. laxum Phillips accession, although the former contained 60% more than the latter. Gossypium raimondii Ulbrich contained principally the unique TA, raimondal. The species in the B, C, F, G and K genomic groups had very low concentrations of gossypol compared to other TAs, however, gossypol was the principal foliar TA in most of the D genome species. In the AD genome, with minor exceptions, all six TAs occurred. Three distinct TA patterns were observed among seven G. laxum accessions. The diversity in biosynthesis and accumulation of TAs among Gossypium species should provide useful germplasm for modifying the TA quality and quantity of cotton. Resource material is also identified to study the metabolic pathways and regulatory mechanisms controlling the synthesis of these compounds.
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