| dc.description.abstract | Guar [Cyamopsis tetragonoloba (L.) Taub] is a legume grown worldwide with low production inputs and costs, tolerant of hot, dry, and saline conditions, with the potential to provide several ecosystem services. Guar production in the U.S. is centered in the Southern Great Plains (SGP). But regional cultivation of guar is challenged by a lack of scientific understanding and limited agronomic advances in several areas, including guar germplasm improvement, biological N fixation (BNF) functions, and alternative cropping systems. To address these issues, three distinct studies were conducted: [1] an evaluation of phenotypic variation and relationships among 50 guar germplasms; [2] a test of drought tolerance on growth and nodulation of guar at various stress levels and recovery functions; and [3] a systems study evaluating integration of guar into regional winter wheat system at different cropping intensities. Results of Study 1 showed phenotypic links between plant capacity to support nodulation, N2 assimilation, and plant biomass production, with genotypic differences in nodule mass, branch numbers, and stem diameter with moderate to high heritability. In Study 2, drought or water stress generally had the greatest negative impact on nodule weight, followed by biomass and reproductive parameters. However, except at extreme water stress levels, drought had little effect on nodule number, indicating that the basic machinery for BNF (nodules) remained largely intact. Both nodule and biomass growth exhibited strong and rapid recovery upon relief of water stress. In Study 3, dry and hot environmental conditions were detrimental to the growth, development, and yield of field-grown guar. Differences among the tested cropping systems were most pronounced in the driest year of the study with the most intensive cropping system exhibiting negative effects of soil water deficit. Among integrated wheat-guar systems, the double-cropping (WG2) system showcased high system productivity over time, but the seasonal likelihood for a productive crop was greater and the risk of crop failure was lower for WG1.3 (1.3 crop/year) under the regional climate. Overall, these studies revealed useful insights for improvement of guar production in the SGP and other guar production regions of the world. | |
