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Molecular evolutionary genetics of crop and weed responses to crowding
Domestication of wild species is characterized by changes in diverse phenotypic traits, including inflorescence architecture, fruit and seed morphology, infructescence shattering, and the timing of developmental events. These changes result from human selection to increase the harvest index and harvest efficiency. Selection for appropriate environmental responses is also important in this regard. For instance, higher planting densities could increase yield in many crop species, but densities are limited by developmental responses to crowding, in which time to flowering decreases and relative allocation to structural organs increases at the cost of agronomically desirable traits such as leaf, root, and fruit production. Regardless of the trait selected in a crop species, agricultural weeds exhibit dramatic and rapid compensatory evolution that increases weed fitness at the cost of crop productivity. Using comparative genetic and genomics tools, the proposed research investigates the genetic basis of phenotypic responses to crowding. The results will contribute significantly to both crop improvement and an understanding of weed evolution that may aid in management.
The research program focuses on crowding responses in Brassica rapa. In addition to the morphologically diverse domesticated varieties of B. rapa, naturalized populations occur in both agricultural fields and disturbed, weedy sites. Thus, this system is appropriate for investigating both the loci targeted during domestication and those underlying adaptation of weed species to agricultural settings. Moreover, the near relative, Arabidopsis thaliana, is a model for the genetic characterization of shade-avoidance responses, facilitating the identification of orthologous loci under selection in B. rapa. The proposed research takes advantage of current genomic tools to investigate the genetic basis of competitive responses in agricultural and natural settings. Specific research goals include 1) identifying quantitative trait loci (QTL) for fitness and traits affecting competitive ability in field settings in B. rapa and A. thaliana, 2) using controlled light environments to identify QTL important for response to specific environmental cues, 3) quantifying evolutionary responses (measured as allele frequency changes) at QTL determining fitness and phenotypic responses to competition in agricultural and disturbed sites, 4) cloning QTL for traits important to competitive ability with the aim of determining both genetic targets for crop improvement and loci underlying evolutionary change in agricultural weeds.