Genetic and Agronomic Studies of Efficiency in Phosphate Utilization by Com (Zea mays L.)

Abstract

Twenty-eight corn inbreds were screened for their growth in pots under two levels of phosphorus, 0.011 ppm and 0.06 ppm in soil solution. Ten inbreds differing in growth under low P were selected to produce a diallel cross. The inbreds showing good growth under low P were Mp68:616, Ph9, CI21E, B14A, and CM104 and those showing poor growth were Ky226, Oh51A, FR9, Va35, and Tx601. The inbreds and their 45 F1 hybrids were planted in the field in two P treatments, low P (0.011 ppm) and high P (0.1 ppm). Seedling dry weight, grain yield, ear length, 100 kernel weight, and P uptake of these genotypes were generally higher under high P. Significant genotype x P interaction mean squares were observed for seedling dry weight, days to anthesis, grain yield, yield components, P concentration, and P uptake. These results suggest differential response of corn genotypes to levels of P fertilization. Combining ability analyses for this 10-entry diallel grown in low and high P were performed for P concentration, P uptake, and grain yield. General combining ability (GCA) and specific combining ability (SCA) mean squares were highly significant for these three characters at both levels of P, suggesting that both additive and nonadditive genes are important in controlling the expression of these three characters. In combined analysis, GCA x P and SCA x P interaction mean squares were highly significant for all three characters. The narrow-sense heritabilities estimated from the low P condition were 32.7% for P concentration, 35.4% for P uptake, and 31.7% for grain yield. These estimates were higher than the estimates in the high P condition. Twelve corn cultivars of diverse genetic background were evaluated for their grain yield in the field under 10 levels of P; 0.003, 0.006, 0.012, 0.025, 0.05, 0.1, 0.2, 0.4, 0.8, and 1.6 ppm in solution. External P requirements of these c o m cultivars were estimated by two regression models; a square root model and a linear-response-plateau model. Corn cultivars differed greatly in grain yield production. Although the external P requirements varied and in general ranged from 0.02 to 0.8 ppm when estimated from the square root model, the external P requirement of most corn cultivars ranged from 0.04 to 0.06 ppm when estimated by the same model. The latter range is tentatively recommended for corn production. External P requirements of these corn cultivars estimated from the linear-response-plateau model ranged from 0.02 to 0.1 ppm. In this study, cultivars with extremely low external P requirements (0.02 ppm) and high yield potential were found which suggests that it is possible to select a corn cultivar with low external P requirement and high yield for areas with soils which have low P availability. Twenty-five corn inbreds were grown under laboratory conditions for 10 days and acid phosphatase (AP) activity of their root extracts was assayed. The AP activity of root extracts of these corn inbreds differed. Six inbreds which differed in the AP activity of their root extracts were selected to produce a diallel cross. General combining ability and specific combining ability mean squares were highly significant, suggesting that additive and nonadditive genes were important in controlling AP activity of root extracts. Genotypes in a 4-entry diallel were grown in nutrient solution with two levels of aluminum. AP activity of intact roots was assayed. Genotypes differed in AP activity of their intact roots, suggesting that corn genotypes differ in the ability to make organic phosphate available. Significant genotype x aluminum interaction mean squares were found for AP activity of intact roots and shoot weight. These results suggest genetic variation in c o m population in their response to aluminum. GCA and SCA for AP activity of intact roots were highly significant at both levels of aluminum treatment indicating both additive and nonadditive genes were important in controlling AP activity of intact roots.