Major Leaf Shapes of Cotton: Genetics and Agronomic Effects in Crop Production

There exist four major leaf shape alleles in tetraploid cotton: normal, sub-okra/Sea-Island, okra, and super-okra. This allelic series has long served as a model genetic locus both in cotton and the broader leaf development research community. Over the years, numerous studies have attributed various production advantages to specific leaf shapes. The objective of this study was to provide a comprehensive review of this literature in order to provide a definitive report on the true benefits of these leaf shapes. In addition, a history of the genetic dissection of the major leaf shape locus was compiled. Leaf shape was found to have consistent effects on boll rot resistance, earliness, flowering rate, chemical spray penetration, lint trash, and yield. Reported effects on various insect resistances, photosynthetic rate, water use efficiency, and fiber quality were not consistent across studies. An ideal cotton cultivar would produce normal leaves up until the point canopy closure is obtained and then it would switch over to an open canopy of okra or super okra. Major leaf shapes of Upland cotton are a multiple allelic series of a single incompletely dominant genetic locus L-D1 on chromosome 15-D1 (Chr15). Genetic analysis studies have precisely mapped the major effect leaf shape genes in cotton and deciphered the causal nucleotide and gene expression changes leading to leaf shape phenotypic diversity in cotton. Recent advances in understanding the molecular processes underlying leaf shape phenotypic changes could help open new avenues for developing cotton cultivars with ideal leaf shape and could enhance sustainable and profitable cotton production. D the vast majority of cotton cultivars carrying “normal (NL)” or broad leaves, there has been periodic interest in the use of the major leaf shape “mutants” to improve particular aspects of cotton production. These alternate leaf shapes; sub-okra/Sea-Island (subOL), okra (OL), and superokra (superOL), have been reported to influence a wide range of characteristics from disease and insect resistance to yield and fiber quality. The four leaf shapes are well-established as alleles at a single locus called L or L-D1. All four are easily distinguishable by brief visual observation (Figure 1) and heterozygotes are intermediate between the parental types.