Monday, November 5, 2007 - 9:45 AM
54-2
Breeding Maize for Total Biomass Production: Examination of Harvest Index and the Relationship between Stover Yield and Grain Yield.
Maize stover will serve as an important feedstock for an emerging lignocellulosic ethanol industry in the U.S. Large increases in stover yield are required to meet national transportation fuel goals established by the U.S. Department of Energy and other federal agencies. Our objective was to determine if breeding for stover yield will be antagonistic to maintaining current genetic gains in grain yield. To do this, we surveyed the literature for reports on the genetic relationship between grain and stover yield of maize. In contrast to what has been observed in small grains crops, where advances in grain yield have been primarily associated with increases in harvest index, the harvest index of temperate maize has not changed, and increases in grain yield have been associated with increases in biomass yield. Modern hybrids produce heavier, healthier plants better able to withstand various types of stresses, especially population density. Studies on the indirect responses of recurrent selection programs have given mixed results depending on selection conditions and germplasm. Those including temperate maize populations indicate that stover yield has either increased or remained constant with recurrent selection for grain yield. When recurrent selection within tropical populations is aimed at increasing grain yield under drought conditions, greater grain yield is achieved through more efficient dry matter partitioning and comes at the expense of stover yield. Within the studies reporting correlations between grain yield and stover yield reviewed thus far, most correlations were significantly positive while none were significantly negative. To this point, we conclude that breeding for increased stover yield will not hinder genetic advances in grain yield within temperate germplasm under drought-free conditions. In fact, because grain yield of maize has been associated with biomass yield and not harvest index, increasing stover yield might help lift the ceiling on grain yield.
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