Genetic Environmental Effects on Silage Productivity of Corn (Zea mays L.)

Lee, Myoung Hoon
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A series of 5 experiments were conducted on silage corn production in Hawaii, with assessment of a variety of genetic and environmental factors. Two corn hybrids were planted bimonthly for 2 years using 6 different population densities, ranging from 50,000 to 200,000 plants/ha. The optimum population density for silage yield was 167,000 plants/ha, but for grain was much lower. Optimum populations for grain under unfavorable seasons (winter) were lower than those in favorable seasons (spring and summer). Significant population x season interaction for grain and stover yields would recommend lower population density in winter planting for silage production in Hawaii. Increasing population resulted in reduction of yield components and plant characters such as height, stem diameter, and leaf area. Grain and stover yields showed seasonal cyclic variations throughout the years, with higher yields in spring and summer, and lower yields in fall and winter seasons. Plant characters and yield components showed similar seasonal variations to those of grain and stover yields. Minimum temperature and solar radiation were important determinant factors for corn production in Hawaii. Brown midrib-3 mutant corn, low in lignin content and high in digestibility, was compared to normal counterpart corn to determine yield response and their components. Significant grain and stover yield reductions were observed bm3, with average reductions of 20% for grain yield and 17% for stover yield. Several hybrids showed small reduction in total yield (6-7 %), indicating possible use of bm3 for high quality corn silage. Mean squares of general combining ability (GCA) and specific combining ability (SCA) were highly significant for grain and stover yields. The GCA/SCA ratio for stover yield was much higher than that of grain yield, indicating that the GCA effect was more important than SCA in stover yields. The GCA/SCA ratio for filled ear length and number of kernels were much higher than those for grain yield. This result indicated that the GCA effect was more significant for yield components than for grain yield. Corn genotypes were evaluated for yields and their characters, under normal daylength (average 12 hours) and extended daylength of additional 4 hours of light in Hawaii. Tasseling and silking were delayed under extended light for all genotypes. Plant characters, including plant height, ear height, number of stem nodes, LAI, and stem diameter increased significantly under extended light. The magnitude of increase for those characters depended on the sensitivity to photoperiod. Significant grain yield reduction was observed, but stover yield increased significantly under extended light. The interval from tasseling to silking was much longer under extended light, creating poor condition for pollination. No difference of total dry matter yield was observed between normal and extended daylength conditions. The increase in stover yield was offset by the decrease in grain yield. Tropical inbreds from wide genetic sources were evaluated for silage yield and plant characters with Hawaiian tester inbreds. Among the 217 hybrids studies, about 5 % of those were superior for silage yields to the Hawaiian superior check hybrid. CIMMYT, H632, and ICA inbreds revealed superiority for silage production. These inbreds also had high GCA effects for grain yield. In general, the superior hybrids selected were later in flowering and maturity. The late maturing hybrids were 10-15 days longer in maturity than early maturing hybrids. The superior hybrids had an advantage for silage production because of much higher yield even in the longer growing period. A 7-entry diallel set based on the factorial experiment was evaluated for silage yield and genetic characters. In general, late maturing hybrids showed higher grain and silage production. Stover yield was correlated with most of the plant characters and rust rating was negatively correlated to grain and stover yields. GCA and SCA were significant for both grain and stover yields. The GCA/SCA ratio indicated that additive genes were more important in the genetic variation. GCA x season and SCA x season interactions were significant for grain and stover yields, indicating that gene effects were not stable for grain and stover yield under dissimilar environment.
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