CARBOHYDRATE-LEVELS IN FIELD-GROWN LEAFY AND NORMAL MAIZE GENOTYPES

Photosynthate contribution to grain yield Is complex depending, in par t, on the translocation of photosynthate within the plant. A 3-yr held study was conducted to compare the distribution of leaf and stem carb ohydrate concentrations of two leafy maize hybrids, both with extra le aves above the ear, vs. a normal hybrid on a loam soil (Typic Eutrochr ept) at Ottawa, Canada (45 degrees 23'N, 75 degrees 43'W). The Leafy 2 hybrid outyielded the Check (both with stay green characteristic), bu t the Leafy 1 hybrid had yields inferior to the other two. Patterns of leaf and stem carbohydrate concentrations with leaf level varied amon g hybrids. This genetic variability could be quantified by fitting dat a to a cubic equation and by calculating mean leaf or stem concentrati ons for the upper canopy. Patterns in total nonstructural carbohydrate s paralleled patterns in sugar concentrations. Leaf carbohydrate conce ntrations were less than one-third those of stem concentrations, showe d more diurnal variation, and appeared to be directly influenced by ph otosynthate production. Mean stem carbohydrates for both leafy hybrids and the Check showed a small rise during the first 10 to 12 d after p ollination (DAP), followed by a decline before 35 DAP, which was large st in Leafy 2. Between 40 and 60 DAP, concentrations in Leafy 1 fell s ightly, while those in Leafy 2 and the Check rose. The larger drop in stem carbohydrates in Leafy 2 could be an indication of greater transl ocation to the grain during early grain fill in this hybrid. The decli ne in Leafy 1 stem concentrations just before black layer mag have pro vided a later source of carbohydrates to the grain. This study suggest s that analysis of canopy carbohydrates may identify the actual photos ynthetic contribution of leaf area to grain yield.