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

Photosynthate contribution to grain yield Is complex depending, in part, on the translocation of photosynthate within the plant. A 3-yr held study was conducted to compare the distribution of leaf and stem carbohydrate concentrations of two leafy maize hybrids, both with extra leaves above the ear, vs. a normal hybrid on a loam soil (Typic Eutrochrept) at Ottawa, Canada (45 degrees 23'N, 75 degrees 43'W). The Leafy 2 hybrid outyielded the Check (both with stay green characteristic), but the Leafy 1 hybrid had yields inferior to the other two. Patterns of leaf and stem carbohydrate concentrations with leaf level varied among hybrids. This genetic variability could be quantified by fitting data to a cubic equation and by calculating mean leaf or stem concentrations for the upper canopy. Patterns in total nonstructural carbohydrates paralleled patterns in sugar concentrations. Leaf carbohydrate concentrations were less than one-third those of stem concentrations, showed more diurnal variation, and appeared to be directly influenced by photosynthate production. Mean stem carbohydrates for both leafy hybrids and the Check showed a small rise during the first 10 to 12 d after pollination (DAP), followed by a decline before 35 DAP, which was largest in Leafy 2. Between 40 and 60 DAP, concentrations in Leafy 1 fell sightly, while those in Leafy 2 and the Check rose. The larger drop in stem carbohydrates in Leafy 2 could be an indication of greater translocation to the grain during early grain fill in this hybrid. The decline in Leafy 1 stem concentrations just before black layer mag have provided a later source of carbohydrates to the grain. This study suggests that analysis of canopy carbohydrates may identify the actual photosynthetic contribution of leaf area to grain yield.