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Application of GOSSYM to Genetic Feasibility Studies. I. Analyses of Fruit Abscission and Yield in Okra-Leaf Cottons¹

The cotton (Gossypium hirsutum L.) model GOSSYM was used to demonstrate how a computerized crop simulation model can be used in a breeding or in an agronomic research program to predict the performance of cottons such as okra leaf when grown under various environmental conditions. The GOSSYM computer simulations indicated that the higher fruit load produced in okra-leaf compared to normal-leaf cottons results from the carbohydrate (not used in leaf material) being used in the initiation of more fruiting sites. Then, as the fruit load increases late in the fruiting period, larger carbohydrate stresses develop in the okra-leaf type than in the normal-leaf crop. The plant simulated by GOSSYM balances those shortages of materials by aborting fruit. The abortion of fruit is higher in okra-leaf than in normal-leaf cotton because it develops a higher fruit load. GOSSYM predicted that the percent fruit retention in okra-leaf cottons was not correlated with N-application rate; however, as the application rate increased, the number of fruiting positions produced also increased. Increasing carbohydrate supply by increasing the photosynthetic rate by 50% improved percent fruit retention at all rates of N. Okra-leaf cottons perform inconsistently under field conditions apparently because the plants fall to produce and maintain sufficient leaf area index (LAI) to intercept enough solar radiation and provide the photosynthate required to meet the fruit growth requirements under adverse growing conditions. Under favorable growing conditions, both normal and okra-leaf types produced a dense canopy; however, the LAI was larger in the normal-leaf type. The more efficient distribution of carbohydrates into the fruits by the okra-leaf type resulted in higher yield. Under adverse conditions, the LAI was lower in both genotypes. However, it remained higher in the normal than in the okra-leaf type, which thereby intercepted more solar radiation and resulted in higher yield. Okra leaf appears superior for yield under optimum conditions, normal leaf under adverse conditions. An intermediate leaf type such as sub okra may be valuable in increasing the stability of cottons to adverse environmental conditions.

Key Words: Gossypium hirsutum L. • Cotton breeding • Crop simulation • Carbohydrate balance • Nitrogen balance • Light interception

² Research associate, Dep. of Agronomy, Mississippi State Univ.; research agronomist, and research geneticist, Crop Sci. Res. Lab., USDA-ARS, Mississippi State, MS 39762.

Received for publication June 8, 1981.