Photosynthesis in guar: Recovery from water stress, basic parameter estimates, and intrinsic variation among germplasm.

Little is known about the photosynthetic physiology of guar (Cyamopsis tetragonoloba L. Taub), a legume crop, including how photosynthetic parameters intrinsically vary among germplasm and their recovery from water stress. To address this, two greenhouse studies were conducted: Study-1 to compare photosynthetic light response (AN–I) curves and related parameters in three contrasting guar genotypes under optimal and post-water deficit conditions; and Study-2 to quantify photosynthetic parameters in 44 guar genotypes and explore inter-relationships with plant growth parameters. In Study-1, the mean net photosynthetic rate (AN) statistically peaked with 1500 μmol (photons) m −2 s −1, though the maximum AN [33.29 μmol (CO2) m−2 s−1] was modeled to occur with 1950 μmol (photons) m −2 s −1. The light compensation point (Icomp), dark respiration rate (RD), and maximum quantum yield (Ф(I0)) were modeled to be 49.9 μmol (photons) m−2 s−1, 2.62 μmol (CO2) m−2 s−1, and 0.0526 μmol (CO2) μmol−1 (photons), respectively. Photosynthesis in guar was resilient to water stress. Despite reductions in growth, specific leaf area (SLA), and other growth parameters, persistently drought-stressed guar plants, on average, exhibited rapid and full recovery of photosynthetic functions when watered. Genotypes differed in their capacity to recover to some degree. In Study-2, AN differed only between two of the 44 genotypes tested, corresponding to the minimum and maximum AN values. There were no relationships between AN and most plant growth parameters. This finding suggested there is low potential to use point measurements of AN as a selection parameter for increased guar productivity. [ABSTRACT FROM AUTHOR]