Bridging Classical and Molecular Genetics of Cotton Fiber Quality and Development

Abstract

Cotton is the single most important natural fiber in the world and represents a vital agricultural commodity in the global economy. Ninety percent of cotton's value resides in the lint fiber. Cotton fiber quality, defined by the physical properties of the lint fibers, is an important part of the cotton manufacturing process from field harvest through ginning and textile manufacturing and is reflected in the end product. The primary fiber properties affecting textile manufacturing and end product quality include fiber length and uniformity, strength, elongation, fineness, and maturity. Numerous techniques and tools to measure these fiber properties have been developed during the last 100 years. Classical quantitative genetics research methods have determined the heritability, components of genetic variance, environmental interactions, and correlations of fiber properties among one another and with fiber yield. In response to the advances made in fiber processing and manufacturing over the course of the 20th and 21st centuries, classical plant breeding based on phenotypic selection has improved fiber quality while also increasing fiber yields. At the same time, intensive phenotypic selection programs have resulted in decreased levels of genetic diversity within the primary gene pool of Upland cotton. Classical plant breeding programs have faced challenges and difficulties transferring new, stably inherited allelic variation from inter-specific hybridization. However, the last 15 years have witnessed an explosion of efforts to utilize molecular biology tools to study the structure, function, and evolutionary relationships of the cotton genome. Much of the first 15 years of molecular genetic research into cotton fiber quality has been devoted to developing core infrastructure including polymorphic DNAmarkers, discrete genetic mapping populations, and extensive nuclear genetic linkage maps. This activity has provided insight into the location, effects, and complexity of the quantitative trait loci (QTL) associated with fiber properties. A fascinating story is being written from the advances being made by combining classical and molecular genetics to explore fiber quality. Although fiber properties are affected by a large number of small effect QTLs, molecular research has also demonstrated that a large percentage of the loci controlling fiber quality properties are present in "gene islands" that are non-randomly distributed across the A- and D-genomes. The next 15 years of molecular genetic research will undoubtedly provide a clearer picture of the genetic basis of cotton fiber quality and the functions of genes controlling various fiber properties. Future research efforts that combine the power of molecular genetics with the knowledge and experience accrued by classical plant breeding will provide portable and inexpensive DNA markers that can be used by plant breeders to select and develop the next generation of high fiber quality cotton cultivars.