Alteration of root and shoot morphologies by interspecific replacement of individual Upland cotton chromosome or chromosome segment pairs

Genetic approaches often lead to the most cost-effective and efficient means to improve crops, especially those grown widely. But for most crops, cotton included, genetic improvement efforts have focused far more on above-ground plant attributes than on root systems. Root system establishment is crucial to cotton seedling success, subsequent development, crop performance and sustainability. As a first step toward genetic enhancement of cotton root systems, significant heritable phenotypic variation must be found or created. The overall objective of this research was to study the effect of substituted chromosomes or chromosome segments from the donor tetraploid species Gossypium barbadense, G. mustelinum, and G. tomentosum on the selected traits of the stem, leaf, and especially root in CS lines. Twenty-seven chromosome substitution (CS) lines, containing different pairs or short segments of chromosomes from G. barbadense (CS-B lines), G. mustelinum (CS-M lines), and G. tomentosum (CS-T lines) and two parents, TM-1, parent quasi-isogenic to the CS lines and G. barbadense 3-79, the donor parent to all CS-B lines, were analyzed. Goals were to determine if CS lines significantly affect any of 17 morphological shoot and root traits. Indeed, significant line-based variation occurred for several root and shoot phenotypes. Comparisons of means and two-way hierarchical cluster analysis revealed several CS lines simultaneously affected multiple shoot and/or root traits, positively or negatively. Pairwise correlations of traits and the cluster analysis showed strong relationships among certain traits. The high correlation among several root traits suggests that easier-to-screen traits might be leveraged strategically to devise breeding-friendly methods for phenotypically evaluating root system morphology. Most importantly, this research identifies CS lines with prospectively novel individual trait effects and others with multi-trait effects that can be further dissected and used to improve our knowledge of cotton root systems, their development, genetic control and genetic improvement.