C ULTIVATED Upland cotton, Gossypium hirsutum L., has leaf, extrafloral, and floral nectaries. The nectar secreted attracts many insects and provides an important food for them. A nectary is usually found on the midrib on the lower side of each leaf. (Figure 1). Extrafloral nectaries are commonly found below the bracts (Figure 2) and also between and inside the bracts. Floral nectaries are located between the sepals and petals. (These have not been studied in the plant material reported in this paper.) G. tomentosum Nuttall is a wild cotton species, native to Hawaii, which has no leaf or extrafloral nectaries. G. hirsutum and G. tomentosum, tetraploid species with 2n = 52 chromosomes, produce a fertile Fj hybrid. Among the many interesting genetic appeared in plants derived from hybrids of G. tomentosum, the absence of leaf and ries was selected for transfer to Upland cot in the transfer program, C.
Male sterility in Upland cotton (Gossypium hirsutum L.) has been produced by mutant genes, cytoplasm from other species, environmental stress, and chemical treatment. Genetic sterilities vary in expression from complete sterility due to a single dominant gene to partial sterility due to recessive genes. The cytoplasmic‐genetic sterile strains with cytoplasm from either G. anomalum Wawra & Peyr. or G. arboreum L. vary in response to genes, cytoplasm, and the external environment. Daily maximum temperature 15 to 16 days before anthesis affects sterility more than any other aspect of the external environment. A‐lines and B‐lines have been produced for pure‐breeding sterile strains, one set for G. anomalum cytoplasm, the other for G. arboreum cytoplasm. All of the commercial strains of G. barbadense L. tested with these two sterilities produced completely fertile F1 hybrids. The commercial cotton crop is largely self‐pollinated. The most critical problem for production of hybrid cotton appears to be finding some way to get the male‐sterile flowers pollinated.
Genetically or cytoplasmically uniform crops may be vulnerable to disastrous pest infestations. Upland cotton (Gossypium hirsutum L.) cytoplasm is present in most of the cotton cultivars grown commercially in the U.S. However, experimental breeding material has been developed from Upland cotton hybrids with cytoplasms from seven other species of Gossypium. The most uniform and productive progenies within each of these seven cytoplasms were selected for making reciprocal backcrosses to Upland cotton cultivars. Backcrosses with cytoplasm from two tetraploid species (G. barbadense L. and C. tomentosum Nutt.) showed no significant differences from their reciprocal hybrids with Upland cytoplasm, but similar backcrosses with cytoplasm from each of the five diploid species (G. herbaceum L., G. arboreum L., G. anomalum Wawra & Peyr., G. harknessii Brandagee, and G. longicalyx Hutchinson and Lee) differed significantly from their reciprocal hybrids.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.