| Two experiments were conducted to study physiological reasons for yield differences among diverse maize (Zea mays L.) cultivars. Growth analysis techniques were used to test the hypothesis that high yields of commercial maize hybrids are due to: (1) high rates of dry matter accumulation, (2) a proportionally larger distribution of assimilates to reproductive growth, and/or (3) longer filling period. Attention was also given to storage of assimilates.;In 1978, the hybrid and inbred ear yields were drastically reduced by poor environmental conditions; however, the hybrid yield was significantly greater than that of the inbred. Stalk refractometric readings per unit land area were higher in the inbred than in the hybrid. This suggested a higher accumulation of soluble solids in the inbred line, probably because of its lower sink capacity.;Except for Nal-Tel, the cultivars compared in 1979 did not significantly differ in CGRv and LAI. However, Coker 77 maintained its high LAI for a longer period than the other cultivars. During reproductive growth, all cultivars showed a decrease in canopy assimilate production. Although CGRr values of Chapalote and Coker 77 were not significantly different, the CGRr of Coker 77 was sustained for a longer period. Maiz Criollo and Nal-Tel had the lowest CGRr values. Partitioning coefficient varied among cultivars. Nal-Tel had the highest PC followed by Coker 77, Maiz Criollo, and Chapalote. Final ear yields for Coker 77, Maiz Criollo, Nal-Tel and Chapalote were 1023, 776, 607, and 578 g m('-2), respectively. Total available carbohydrates were higher in the plant components of Coker 77 than in the other cultivars. Contributions of remobilized TAC from vegetative components to final ear yield were estimated to be 9, 13, 21, and 26% in Coker 77, Maiz Criollo, Nal-Tel, and Chapalote, respectively.;Similar CGRv values in Chapalote, Coker 77, and Maiz Criollo indicated similar potential to produce high yields. Chapalote, however, produced many barren tillers in addition to ear-bearing stalks. This tillering habit of Chapalote explains its lower PC and yield. Nal-Tel had the highest PC, but its ear yield was low probably because of its low LAI. Length of filling period, either as EEFP or ESFP, was not a significant factor in yield differences. Coker 77 had the highest EGR; differences in EGR accounted for most of the yield differences among cultivars.;In 1978 the single-cross hybrid Pioneer Brand '3369A' was compared with the inbred line Iowa B37, and in 1979 the hybrid 'Coker 77' was compared with two ancient Mexican races, 'Chapalote' and 'Nal-Tel', and a Cuban accession, 'Maiz Criollo'. These experiments were planted at the University of Florida Agronomy Farm in Gainesville at population densities expected to give approximately equal leaf area indices (LAI). Refractometric readings per internode and per unit area were determined in both experiments. Also, in 1979 total available carbohydrate (TAC) in plant components (stalk, leaf, cob, and grain) were measured. Rates of dry matter accumulation (crop growth rates), computed during the vegetative (CGRv) and reproductive (CGRr) phases, were examined as estimates of canopy capacity to produce assimilates. Ear growth rates (EGR) were also determined. The partitioning coefficient (PC) was used as an estimate of assimilate distributed to ear growth as opposed to vegetative growth, and effective ear filling period (EEFP) and effective seed filling period (ESFP) were estimates of filling periods.;The results of these experiments suggested that under conditions of similar LAI, the physiological characteristics of a high-yielding maize cultivar are high PC, high EGR, and a longer duration of CGRr. |
