Application of GOSSYM to Genetic Feasibility Studies. II. Analyses of Increasing Photosynthesis, Specific Leaf Weight and Longevity of Leaves in Cotton1

Abstract

The model GOSSYM was used to demonstrate how a computerized crop simulation model can be used in a breeding or agronomic research program to simulate the performances of genotypes with different physiological response when grown under various environmental conditions. Results of simulating a cotton (Gossypium hirsutum L.) crop with higher leaf photosynthetic rate indicated that cotton lint yield could be increased up to 54% by increasing photosynthetic rate by 30%, providing that adequate N and water were available. With 30% increase in photosynthetic rate the high water (375 mm) input outyielded the low water (186 mm) treatment in both 56 and 112 kg/ha of N treatment, however, no difference in lint yield was obtained between the water regimes at 336 kg/ha of N. Maturity was delayed in the higher water treatment. Simulation results indicated a higher N requirement to obtain maximum lint yields with a cultivar having increased photosynthetic rate. It was concluded that if the increased CO₂ exchange rate observed in a genotype were associated with increased specific leaf weight, more of the CO₂ fixed would be used in the production of thicker leaf rather than lint production. This suggests caution in using specific leaf weight to select indirectly for higher leaf photosynthetic rates in cotton. Keeping the leaves photosynthetically active for a period of up to 70 days resulted in a higher leaf area index (LAI), the crop intercepted a higher fraction of the incoming solar radiation, and produced a higher lint yield. This seems to be a more promising characteristic to be used as criteria in a breeding or agronomic research program oriented toward increasing lint yield.