Variability in Fluorescence and Photosynthesis of Sorghum Genotypes to Cold and Drought Stress.

Sorghum bicolor (L) Moench is a promising bioenergy crop because of its high level of biomass production and tolerance to environmental stress, especially drought. Portable fluorescence and photosynthesis meters can be used to evaluate a large number of genotypes, exploit the sorghum genetic diversity and discover genes associated with stress tolerance. The objectives of this study were: 1) to determine the phenotypic diversity in fluorescence and photosynthesis of sorghum genotypes subjected to drought and cold stress and their subsequent recovery; and 2) to develop an accurate protocol for high-throughput phenotyping of sorghum plants to be used in linkage disequilibrium (LD) studies. Twelve genotypes from diverse origin were grown in growth chambers under two cold treatments with contrasting stress duration (5 and 7 days), and control conditions. Temperatures used were 28/24 °C (day/night) for control and 10/10 °C for cold conditions. After cold stress, control temperatures were reestablished for recovery evaluation. For drought experiments, plants were subjected to two final water levels (5% and 15% volumetric water content) after which they were re-watered. A wide range of responses were found for fluorescence parameters (non photochemical quenching, PhiPs2, Fv/Fm) and photosynthesis; and based on these results, the optimal cold and drought conditions were selected for future LD studies.