Gas exchange and time to reach maximum rate of photosynthetic rateand their relationship with whole-plant traits in sugarcane in water abundant Louisiana, USA

Variety development of sugarcane (Saccharum spp. hybrids) is necessary to continue to improve sugar yields, and selecting for photosynthetic traits can improve carbon inputs for sugar production beyond just the increase in carbon allocation to sugar production. In this study, gas exchange and whole plant measurements were made on 55 sugarcane genotypes in Louisiana. All traits had significant genotype effect and phenotypic variation was consistent among replicates of each variety. Variation in the relationship between CO₂ assimilation and stomatal conductance suggests that sugarcane exhibit variation in both photosynthetic capacity and CO₂ substate availability. Genotypes with insensitive stomates that exhibited a short time to reach physiological steady state had greater cumulative photosynthesis during transitory periods. Temporary shading and fluctuating light are common in the field, so increasing stomatal insensitivity may improve photosynthesis in sugarcane in Louisiana. Whole plant traits showed that leaf area matters in that genotypes with greater canopy leaf area and leaf mass had larger stalk mass and volume. Gas exchange traits were not correlated with whole plant traits, even though there are implicit relationships between photosynthesis and whole plant growth and water loss. The relationship between leaf and whole plant traits needs to be better understood to identify suitable physiological traits and develop more accurate selection methods that lead to increased genetic gain.