Dry Matter Accumulation in Maize Hybrids Near Isogenic for Endosperm Mutants Conditioning Protein Quality 1

Six near isogenic genotypes of four maize ( Zea mays L.) single‐cross hybrids were grown in a randomized complete block design with a split‐split‐plot arrangement of treatments with four replications. The genotypes were sugary‐2 ( su2 ), waxy ( wx ) and opaque‐2 ( o2 ), the double mutant combinations [sugary‐2 opaque‐2 ( su2 02 ) and waxy opaque‐2 ( wx o2 )], and the normal counterpart. The plants in each plot were sib‐pollinated twice by hand to insure full seed sets. Harvests were made at 7‐day intervals beginning 10 days after pollination (DAP) and continuing through 73 DAP. The purpose of this experiment was to determine the effect of the six genotypes on kernel dry matter accumulation (grain weight), cob weight, and grain moisture percentage during the grain filling period. On the average su2 , o2 , wx o2 , and su2 02 accumulated 13, 18, 20, and 25% less grain weight than normal. The reduction in kernel dry matter accumulation was the result of shorter grain filling periods and less rapid rates of grain filling during the reproductive phase. Waxy accumulated 4% less grain weight than normal. The lower grain weight accumulation of wx was because of a less rapid rate of grain filling and not because of a shorter grain filling period. Opaque‐2 and su2 o2 showed a 9 and 11% reduction of cob weight, respectively, compared to the normal hybrids throughout development. Waxy, wx o2 , and su2 hybrids were similar to normal in cob weight accumulations. All of the genotypes retained a higher moisture percent during development than their normal counterpart hybrids. However, on the average, 02 was not significantly different in moisture than normal at 73 DAP.