Genotypic Difference For Sweet Corn Grain Quality Traits And Its Response To Eenvironmental Factors

The genotypic differences for grain quality were studied using the sweet corn varieties or lines released in recent years in China as materials. The correlations between sugar components accumulation and enzyme activities associated with sucrose metabolism during filling grain were clarified. In addition, the fresh ear yield and grain quality response to environmental factors (fertilizer such as N K2O application amount, low light, high temperature and water stress during grain filling) were researched. The main results were as follows.1. Genotypic difference of kernel quality traits for sweet cornThe contents of soluble sugar, reducing sugar, starch, protein, fat, pericarp and dregs and microelements and the grain textural properties (hardness, fracturability, adhesiveness, springiness, cohesiveness, chewiness, resilience) were significantly different among40sweet corn varieties. Among those parameters, the ranges of content of soluble sugar content, pericarp and dregs content were ranged from12.40%to21.00%and from7.90%to15.30%, respectively. The highest coefficient variation (CV) value of grain textural properties was fracturability and the lowest value was cohesiveness. The variation ranges for fracturability and cohesiveness were5308.34～1152.66and0.27～0.16, respectively. Significant correlations were observed among different grain textural properties. The correlation coefficients between hardness and chewiness, resilience and cohesiveness were reached0.90or more. Principal component analysis was performed based on7parameters of textural profile analysis (TPA). Top3factors were transferred and the cumulative contribution to variance was up to86.88%. Hardness and fracturability were the dominant factors. By cluster analysis,40sweet corn varieties were classified into2clusters according to the values of hardness and resilience. According to the values of fracturability and adhesiveness,40sweet corn varieties were classified into4sub-clusters. The grain textural properties of sweet corn were different among genotypes, which could afford references for its utilization.2. Dynamic change of carbohydrate accumulation and enzyme activity associated with sucrose metabolism during grain filling of sweet cornDuring grain filling,100-fresh-kernel weight first increased and then decreased, while grain starch, pericarp and dregs content were gradually increased. The100-fresh-kernel weights of Yangtian2and Chaotian135peaked on the22day after pollination (DAP), which were35.77g and37.63g with kernel water content were65.22%and67.28%, respectively. Accumulation dynamics of grain dry weight of two sweet corn hybrids could be fitted by Richards equation. The maximum grain-filling rate (Tmax) appeared on the16-17DAP. Tmax of Yangtian2was0.2g/d higher than that of Chaotian135. The grain filling duration and theory maximum100-dry-kernel weight were5.1d, and1.24g lower than that of Chaotian135, respectively. The contents of starch and pericarp raised gradually with grain filling. Contents of total soluble sugar (TSS), sucrose and water soluble polysaccharides (WSP) raise first and fall later. Contents of glucose, fructose, and mannitol fall first and raise later. Dynamic of sorbitol content was different between Yangtian2and Chaotian135. The maximum contents of TSS were101.99mg/g FW, and98.25mg/g FW in Yangtian2(DAP22d) and Chaotian135(DAP18d) respectively. The dynamic changes of activities of sucrose phosphate synthase (SPS), sucrose synthase (SS) synthesis were similar changes of TSS and sucrose content. The activity of SS cleavage was gradually increased with the grain developing. Activities of SPS, SS (synthesis) were significantly positive with contents of TSS and sucrose, while SS (cleavage) was negatively correlated with contents of glucose and mannitol. Sugar accumulation of kernel was cooperative action in SPS and SS.3. Effects of N rates on yield, quality and enzyme activity associated with sucrose metabolism of sweet cornThere were four nitrogen rates, N0,75,225and375kg/ha. With the increment of N rates, the fresh ear yield of Yangtian2and Chaotian135were significantly increased and peaked at N225kg/ha treatment. Compared with no-nitrogen treatment, the yields under N225kg/ha treatment of Yangtian2and Chaotian135were increased65.15%and99.61%respectively. The contents of soluble sugar and sucrose were increased by N rates and peaked at N225kg/ha treatment. N rates affect the textural properties of sweet corn. With the increment of N rates, the grain hardness was increased and the fracturability raise first and fall later and peaked at N225kg/ha treatment. The higher yield and quality under N225kg/ha treatment was due primary to the higher activities of SPS and SS (synthesis).4. Effects of K2O rates on yield and quality of sweet cornThere were five potassium fertilizer (K2O) rates,0,75,150,225and300kg/ha. With the increment of K2O, the fresh ear yield, the soluble sugar and sucrose contents raise first and fall later, the starch content fall first and raise later, while the residue ratio gradually increased. Compared with blank, the fresh ear yield of Chaotian135and Yangtian2were significantly increased by potassium fertilization and peaked at K2O150kg/ha treatment, which were increased by15.26%and19.52%, respectively. The textural properties of grains were changed by the K2O rates. The hardness of grains is significantly increased with the increment of K2O rates, and the fracturability raise first and fall later and peaked at K2O150kg/ha treatment. The results from regression analysis indicated that the optimum amounts of potassium fertilization are K2O151.9-164.8kg/ha for the high yield, and K2O150.8-176.6kg/ha for the high quality.5. Effects of low light stress during grain filling on yield, quality and enzyme activity associated with sucrose metabolism of sweet cornA split plot experiment was conducted under field conditions to study the effects of low-light stress (shading degree of50%) during grain filling using two sweet corn cultivars (low light sensitive hybrid Xiantian5and low light tolerant hybrid Huazhen). The growth process of sweet corn was delayed, the fresh ear and kernel weight, sugar content, ear length, ear diameter, kernel number, kernel weight and fresh ear weight were significantly decreased while kernel water content and barren tip were increased under shading treatments. The response of those characteristics to weak light stress were different between two varieties. The fresh ear weight, maximum fresh-100-weight and content of soluble sugar in Xiatian5were reduced significantly by42.6%,31.3%and19.5%, respectively, while those parameters in Huazhen were decreased by20.3%,19.8%and10.1%, respectively. The activities of SPS, SS (synthesis and cleavage) were reduced by shading, while appearance time of maximum SPS activity was delayed. The results indicated that the decrement of yield and quality were due to the restrained photosynthesis, which leading to insufficient of photosynthetic products. More importantly, the reduced enzyme activities associated with sucrose metabolism decreased the sugar accumulation and the transportation and distribution of photosynthetic products to grain.6. Effects of heat stress during grain filling on sugar accumulation and enzyme activity associated with sucrose metabolism in sweet cornThe trial was carried out in artificial phytotron using two sweet corn cultivars with two typical temperature treatments (high temperature, HT and control, CK) during grain filling. The growth process of sweet corn was accelerated, the weight and quality of kernel was decreased seriously under heat stress. The fresh grain weight and kernel water content were reduced, while content of pericarp was increased. At the optimum harvest stage of fresh ear (with kernel water content68%-74%), the fresh kernel weight of the two cultivars was decreased by20.8%(Xiatian1) and16.4%(Yuetian16) under heat stress, respectively. The contents of soluble sugar and sucrose raise first and fall later with the grain development. Heat stress decreased the sucrose content and increased starch content. Heat stress decreased the activities of SPS and SS (synthetic) and increased the activity of SS (cleavage), which inevitably leading to the decrease in sucrose content and deteriorate the kernel quality. The maximum SS (synthetic) activity in process of grain filling of two sweet corns appeared earlier under heat stress, the peak of SPS activity appeared earlier in Xiatian1and did not in Yuetian16.7. Effects of water stress during grain filling on sugar accumulation and enzyme activity associated with sucrose metabolism in sweet cornA negative pressure water supplying and controlling pot device was used to control different soil moisture contents (SMC) by setting the water supply tension of the device at different values. The effects of water stress (relative SMC was90%,75%, and60%, indicated the water supply was excessive, moderate, and deficient respectively) during grain filling on grain yield and quality were studied. The maximum100-fresh-kernel weights were reduced significantly by9.63%(Huazhen) and21.95%(Yuetian16), and soluble sugar contents were decreased significantly by9.37%(Huazhen) and13.64%(Yuetian16) when SMC was excessive. The maximum100-fresh-kernel weights were dropped significantly by11.63%(Huazhen) and 20.46%(Yuetian16), and soluble sugar contents were reduced by9.91%(Huazhen) and12.56%(Yuetian16) under water deficit treatments. Compared with control, the grain growth process was accelerated but the growing period was shortened under water deficit treatment. The grain weight, sugar content and the activities of SPS and SS were improved during early grain filling stage under SMC deficient, but those parameters were decreased during medium and late grain filling stage. The kernel weight, sucrose content and activities of SPS and SS in sweet corn significantly decreased, whereas pericarp and dregs content increased under SMC excessive applied treatments. In conclusion, soil moisture stress leaded to a reduction in grain yield and a deterioration in kernel quality.