| Establishment of accurate yield and quality evaluation system could accelerate the development of varietal experiments of sweet and waxy corn in China. In the study, sweet and waxy corn varieties of varietal experiment in southeast region, China, 2003-2006 were taken as materials. And data of varieties in four regions (Northeast and north China, Huanghuaihai, Southwest and Southeast) in recent years was taken as reference to establish yield and quality evaluation index. The influencing factors for evaluation on variety yield and quality traits were analyzed, and the new idea on establishment of varietal evaluation system was clarified. The main results were as follows:1. Influencing factors of evaluation on variety yield in sweet and waxy corn varietal experiment There were significant differences in the percentage of bract and silk weight, pedicel weight, and commercial ear weight to all ear weight among sweet corn varieties as well as among waxy corn varieties. The percentage of bract and silk weight accounted for 11.24%-40.25% and 9.16%-32.66% in the yield when it was reckon in yield in sweet and waxy corn varieties, respectively. 2.64%-8.93% and 1.66%-8.04% of the yield was unvalued when the yield including ear pedical in sweet and waxy corn varieties, respectively. And the percentage of commercial ear to all ear was only 51.76%-78.57% and 59.75%-72.30% in sweet and waxy corn varieties, respectively. Among various ear yield calculating methods, the yield was -12.64%-35.75% and -2.13%-41.96% higher than the commercial ear yield when it was calculated with the first ear excluding bract and pedicel in sweet and waxy corn varieties, respectively. The yield was 0.09%-35.75% and 0.26%-43.85% higher than the commercial ear yield when it was calculated with all net ears including bract and pedicel in sweet and waxy corn varieties, respectively. And the percentage of increment was significantly different in varieties. Among various kernel yield calculating methods, the kernel yield was -19.23% - 17.61% and -2.34% - 37.16% higher than the commercial kernel yield when it was calculated with the kernel weight of first ear in sweet and waxy corn varieties, respectively. The kernel yield was 0-17.61% and 0-38.81% higher than the commercial ear yield when it was calculated with the kernel of all the ear in sweet and waxy corn varieties, respectively. And the percentage of increment was significantly different in varieties.There were significantly positive correlations between ear water content and kernel water content for all the varieties. And there were significantly negative correlations between net ear weight and ear water content, between 100-kernel fresh weight and kernel water content for most varieties. The increment of ear weight excluding bract and pedicel was 0.40-2.40g for sweet corn and 0.78-3.36g for waxy corn when ear water content decreased 1%. The increment of 100-kernel weight was 0.18-0.75g for sweet corn varieties and 0.64-0.92g for waxy corn varieties when kernel water content decreased 1%. And the increment was different among varieties.2. Quality and kernel components differences at different days after pollination(DAP) among sweet and waxy corn varieties In present evaluation system,even the varieties have similar appearance quality grade, the differences of appearance quality scores could reach 16.7%-20.0% of the total scores. For the same variety, the appearance and eating quality scores were still different in various experimental locations and years. And compared with CK, the ranks of the variety were also different in various locations and years. The eating quality score was significantly different at various harvesting times. The maximal eating quality score occurred at 17-23 DAP and 21-25 DAP for sweet and waxy corn varieties, respectively, and during the stage, the day that maximal score occurred was different for varieties. For the same variety, the day with the best eating quality was different in different years. There were significant differences in soluble sugar content, sucrose content, reducing sugar content, fructose content, crude starch content, lysine content in kernels, Pericarp and dregs content (PADC) and kernel output rate (KOR) at different harvesting times among sweet corn varieties. There were also significant differences in crude starch content, soluble sugar content, PADC, starch viscosity traits (PV, TV, FV, SB, and BD) and KOR at different harvesting times in waxy corn varieties. In sweet corn varieties, along with the postponing of harvesting time, the dynamic changes of soluble sugar content, sucrose content in kernels and eating quality scores were similar, reducing sugar content, fructose content, lysine content and water content gradually decreased, while crude starch content and PADC gradually increased. In waxy corn varieties, along with the postponing of harvesting time, crude starch content and PADC gradually increased, soluble sugar content and water content gradually decreased, while starch viscosity traits didn't occurred clear tendency. At period with best eating quality, kernel quality components were significantly different in sweet and waxy corn varieties, which showed distinctly varietal characteristics, and only kernel water content was comparatively invariableness among varieties, which centralized in 68%-74% and in 59%-64% for sweet and waxy corn varieties, respectively.3. Eating quality influencing factors and establishment of easy operate and objective quality evaluation indecies The results of polynomial stepwise regression analysis and correlation analysis showed that "sweetness" and "pericarp thickness" were important in determine the eating quality scores, and higher values of soluble sugar content and lower values of PADC could result in higher eating quality scores, but other quality components including sucrose content, reducing sugar content, fructose content, crude starch content and lysine content in kernels had no significant effects on eating quality scores in sweet corn varieties. In waxy corn varieties, "viscosity" and "pericarp thickness" were important in determine the eating quality scores,and higher values of crude starch content, starch viscosity and lower values of PADC could result in higher eating quality scores.In the study, objective quality evaluation indecies were clarified, which were soluble sugar content and PADC for sweet corn varieties; crude starch content, starch viscosity and PADC for waxy corn varieties. Objective quality evaluation indecies avoided the subjective affection in present eating quality evaluation methods.4. Evaluation system establishment for yield and quality in varietal experiment The quality was best,kernel quality components content (soluble sugar content for sweet corn varieties and crude starch content for waxy corn varieties) was high, and the differences of yield and quality could reflect the intrinsic differences of varieties when kernel water content was 68%-74% for sweet corn varieties and was 59%-64% for waxy corn varieties, and ear water content was 69%-75% for sweet corn varieties and was 60%-65% for waxy corn varieties. 33.3%-50% of sweet corn varieties, and 37.5% of waxy corn varieties were not at the period with the best eating quality when the ear was harvested at the same DAP,which indicated that the kernel water content and ear water content should be adopted as the harvesting index.In yield evaluation system,the standard commercial ear was that the ear part excluded unvalued parts (mildew ear, bract and silk, barren ear tip, pedicel, and damnification part), and the length was longer than 10 cm. Under the fitting water content conditions, the plot ear yield was calculated using the commercial ear and plot kernel yield was calculated using the kernels denuded from the commercial ear.The improved appearance quality evaluation indecies were more precise and easier to operate. The improved eating quality evaluation were mainly base on objective physical and chemical indecies, viz., soluble sugar content, PADC for sweet corn varieties, and crude starch content, starch viscosity and PADC for waxy corn varieties. At the same time, a general evaluation on ear eating quality could be given by comparing the variety with CK, and the general evaluation was worked out as three ranks (better than CK, inferior to CK, and similar to CK), which were easier to operate. Considering of the appearance quality, eating quality and kernel quality components, the standard of better quality for sweet corn variety was that appearance and eating quality scores and kernel soluble sugar content of the variety were not less than CK, and PADC was not more than CK. The standard of better quality for waxy corn variety was that appearance and eating quality scores,kernel crude starch content and PV of the variety was not less than CK, and PADC was not more than CK. If only one of the three traits (crude starch content, PV or PADC) didn't reach to the above requirements, the variety could also be regarded as similar to CK.
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