| Vegetable soybean [Glycine max (L.) Merrill] is a large seeded soybean, which isharvested at R6-R7stage when seeds are immature and pods are not turning yellow. As a nutritious, healthy and good taste food, vegetable soybean is more popular allover the world. China is the largest vegetable soybean producer and supplier in theworld. However, the quality of China’s vegetable soybean still lags behindinternational statndard due to the late development of vegetable soybean industry andlack of research. Examining the quality of vegetable soybean, especially the ediblequality is the basis for vegetable soybean industry development.The present study investigated the differences in fresh pod yield and seed chemicalcompositions of30vegetable soybean varieties at edible stage; screened out the mainyield components of vegetable soybean by stepwise regression and path analysis;analyzed the correlations between seed chemical compositions and edible quality;determined the key component for vegetable soybean edible quality using principalcomponent analysis and correlation analysis. The accumulation of main qualitycompositions (sucrose, protein, oil, free amino acid, fructose+glucose, raffinose andstachyose) and regulation by key enzymes were investigated using three vegetablesoybean varieties differing in seed sugar content; the effects of nitrogen fertilizationrate and planting dates on the formation of fresh pod yield, edible quality as well askey enzymes activities were analyzed. The main results of the study were as follows:1. One-seed pod,2-seed pod,3-seed pod, plant height,2-seed pod width,2-seedpod length, and100-fresh seed weight were the most important traits in the yieldformation of vegetable soybean. The equation established through these seven traitsby stepwise regression estimated fresh pod yield well because the equation had thehighest multiple correlation coefficient (0.961) and the lowest standard error of theestimates (10.462). Path analysis further indicated that2-seed pod and3-seed podwere the most crucial yield components due to their greatest and positive direct effecton fresh pod yield with path coefficient of0.56and0.58respectively.2. Vegetable varieties differed in scores for edible quality. The cumulativecontribution of sucrose, fructose+glucose, raffinose, stachyose, protein, free aminoacid and oil to edible quality was67.8%. The first group principle component ofsucrose, free amino acid and protein contributed25.7%, the second group of raffinose,stachyose and oil contributed25.2%, and the third group of fructose+glucosecontributed16.9%of the variances. A significant and positive relationship was foundbetween edible quality score and sucrose content (0.864**); while a significant and negative relationship was found between edible quality score and protein content(-0.439*).3. The seed sucrose content of vegetable soybean increased in the early seed fillingstage and decrease in late seed filling stage. The accumulation peak of seed sucroseappeared on the edible stage, namely42days after flowering. The seed sucrosecontent in cv.121was51.8mg/g at edible stage which was33.9%and16.6%greaterrespectively than that of Tai292and CAS No.1. The seed protein content in Tai292was421mg/g which was the highest among the three varieties tested at edible stage.Seed oil content also increased during seed filling stage, and the variety with lowerprotein content had higher seed oil content. The highest seed oil content at ediblestage was178mg/g in cv.121which was10.9%and7.8%higher than that of CASNo.1and Tai292respectively. The seed free amino acid content was high in earlyseed filling stage and maintained at relatively lower level in the middle and late seedfilling stage. The highest seed free amino acid content at edible stage was7.1mg/g inCAS No.1which was13.5%and28.0%higher than that of Tai292and cv.121respectively.4. The seed fructose+glucose content of vegetable soybean decreased during seedfilling stage and the highest value was only3.68mg/g at edible stage. Theaccumulation of raffinose and stachyose were similar to that of fructose+glucose,and their content was only1.3-1.6mg/g and2.5-3.3mg/g. The variation of these threesugar contents was small, and thus had limited effects on eating and nutritional qualityin vegetable soybean.5. The changes of Sucrose Phosphate Synthase (SPS), Sucrose Synthase (SS), AcidInvertase (AI) and Neutral Invertase (NI) activities were consistent to the changes ofsucrose content during seed filling satge. Variety with higher seed sucrose contentconstantly had highest key enzymes activities and thus faster sucrose metabolic rate.Different enzymes had different functions in the processes of sucrose metabolism, andtheir activities differed in seed tissues.6. SPS played an important role in seed sucrose accumulation, was not the onlyenzyme controlling sucrose accumualtion. The difference of sucrose synthesis enzymeactivities (SPS) and sucrose decomposition enzyme activities (SS+AI+NI) waspositively correlated with seed sucrose accumulation (r=0.530**). Vegetable soybeanseed protein accumulation was regulated by Glutamine Synthase (GS). The GSactivity of CAS No.1was much higher than the other two varieties in the early seedfilling stage, while highest GS activities were found in cv. Tai292from edible stageto late seed filling stage. All these changes in GS activities were consistent to theaccumulation of protein content.7. Appropriate N application was benefical for root development in stimulating rootdry matter accumulation, increasing surface area, and enhancing nutrient absorptioncapacity. Excessive N application inhibited root growth, reduced the number of2-seed pod and3-seed pod and thus reduced the fresh pod yield. Excessive Napplication also decreased vegetable soybean eating quality.8. Nitrogen application influenced seed protein accumulation of vegetable soybean.The seed protein content decreased with the increase in nitrogen application rate in early seed filling stage. The seed protein content from N100, N200N300nitrogenapplication rates were2.5%,3.2%and8.5%lower than that of without nitrogenapplication (N0) at edible stage, and was higher in the late seed filling stage. The GSactivity of vegetable soybean seed without N was higher in early seed filling and wasthe lower in late seed filling stage. The effect of N application on seed sucrose contentwas in the order of N100> N0>N200>N300at edible stage, while the seed activitiesof SPS, SS, AI and NI was constantly in the order of N100> N0>N200>N300duringseed filling stage.9. The fresh pod yield of vegetable soybean varied across the years, delayingplanting date consistently reduced the fresh pod yield. The decline in2-seed pod and3-seed pod was correlated with the yield reduction. Delaying planting date was notbeneficial to the eating quality of vegetable soybean. The seed protein content wasincreased by0.8-6.9%, seed sucrose content was decreased by7.6-45.4%and seedraffinose and stachyose content was slightly increased after delaying planting datefrom3May to15May,27May and8June. A synergistic change between theactivities of SPS, SS, and NI and seed sucrose content was found, and delayingplanting reduced these enzymes activities. However, the change of AI activity afterdelaying planting date was not obvious. The GS activity increased after delayingplanting date and its activities differed among varieties. |
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