| Because of its strong adaptability and versatile purposes, nowadays sweet potato has been playing great roles in food security and processing industry in China. Based on the previous experiment that six different types of cultivars in sweet potato had been choosed from 48 varieties or lines of breeding germplasm, and established in the ecological condition of Chongqing, this thesis mainly researched physiological traits such as photosynthetic characteristics, endogenous hormones, distribution of nitrogen and potassium, starch metabolism, and highly efficient planting mode controlled by physical and chemical measures, systematically contrast the difference and dynamic changes of different sweet potato varieties and types during tuberous root thickening. Through correlation analysis, the relationship among every trait of sweet potato was been obtained, which would provide theoretical foundation and base for high-efficiency breeding and high-yield cultivation of different types of sweet potato. The main experimental results were as follows.1. Contrast on photosynthetic characteristics of different types of sweet potatoThe research that contrasted photosynthetic pigment from six varieties of sweet potato suggested that the relative content of chlorophyll in Mianfen-1 leaves was higher. There was no significant difference between others, and no remarkable relationship between chlorophyll content and content of starch or dry matter. The regression curves, concerned with photosynthesis and photo intensity, indicated that Pn of every variety had changed parabolically with PAR increasing. The theoretical LCP of high-starch type of sweet potato was lower than that of low-starch type. Both the maximum of Pn and theoretical LSP from Yushu-2 were higher, while both of them from Yushu-10 were lower. During thickening, the changing trends of Pn, Tr, Gs, WUE every cultivar were different absolutely. However the changing curves about Ci and Ls were same basically. The photosynthetic rate was influenced by both stomatal limitation and non-stoma limitation. For different types, Pn and Tr of low-starch type were more apt to be affected by environmental temperature, and Pn of high-starch type was more stable. For all cultivars, the correlativity analysis suggested that the related coefficient between Tr and biomass was remarkably negative, there were significantly positive correlativity between Gs and Pn, and large significantly positive correlativity between Gs and Tr. For high-starch type, there was markedly positive correlation between Pn and Tr, Pn and Ci. For low-starch type, there were markedly positive correlation between Pn and tuberous roots yield, negative correlation between Tr and starch yield.2. Nitrogen and potassium distribution of different types of sweet potato during thickeningIn dry matter of vines or tuberous roots, the nitrogen content that decreased gradually after tuberous root formation accounted for 2% in vines, and it in tuberous root changed a little during thickening. The potassium content both in vines and in tuberous root was relatively stable. For distribution of N and K, N content in vines was far more than it in tuberous root, while K content was on the contrary. For high-starch type, N content of tuberous root ranged from 0.68% to 0.86%, and that of vine did from 1.98% to 3.32%; for low-starch type, N content of tuberous root and vine ranged from 0.69% to 0.86% and from 2.00% to 3.17% respectively. Correspondingly. for the part of high-starch type, K ranged from 5.83% to 6.66% and from 3.19% to 3.70%; for low-starch type, K ranged from 6.12% to 6.36% and from 3.48% to 3.90%. In addition for high-starch type, the changing range of K content was larger than that for low-starch. While K content of vine was relatively higher for low-type. Correlative analysis for all varieties suggested that K was related with N positively in root. And K in vine was closely related with the K content ratio of root to top negatively. For high-starch type, there were remarkably significant relationship between K content in vine and percentage of dry matter, and between K. content ratio of root to top and commercial percentage; and there was remarkably negative correlation between K content of root and biomass. For low-starch type, there were markedly positive correlation between N content in vine and biomass, large markedly positive correlation between K content in vine and biomass, and notably negative correlation between K content in vine and starch yield.3. The starch metabolic difference of different types of sweet potatoAGPP was essential for starch synthesis and accumulation. Its activity descended with environmental temperature declining and took on a marked difference between two types of sweet potato during thickening. Moreover it could not be the decisive factor of starch content in sweet potato. In this period, both SS and SPS activities were higher in high-starch type. For reducing sugar of all cultivars, its content was relatively high at initial thickening phase and at late stage, and it was relatively low at middle stage. However soluble sugar content fluctuated little during all the time. Except that, the content of two kinds of sugars was higher in low-starch type while the starch accumulation was higher in high-starch type. At the same time the percentage of different sizes of starch granules was not same for all cultivars, majority of granules appeared pellet-shape, and they almost were single-granule starch. The correlation analysis showed that the reducing sugar in root was very significantly and positively correlated with tuberous root yield, very significantly and negatively with dry matter content, significantly and positively with biomass. Moreover soluble sugar and tuberous root yield took a very significantly positive relationship, while the relationship was significant negative both between soluble sugar and dry matter content and between soluble sugar and starch yield. For high-starch type, there were all the significant positive relationship between SPS activity and commercial percentage, between soluble sugar and starch yield, and between soluble sugar and SS/SPS. For low-starch type, SPS activity was markedly and positively correlated with starch yield, and soluble did same with tuberous root yield. Also SS/SPS did same with biomass, but it did very significant and negative with starch yield.4. Dynamic comparison of endogenous hormones in different types of sweet potatoThe results showed that at initial thickening phase, the content of ZR,IAA and ABA in leaves increased, and it began to decline differently at last phase. At the time of 110 days after transplantation, the content of the three hormones was relatively high for Mianfen-1, Yushu-2 and S1-5. Otherwise the ZR, IAA, GA3 and the ratio of the sum of them to ABA were lower at the middle phase of thickening, and the corresponding ratio of Nanshu-88, Beijing-2 and Yushu-10 went up remarkably. For different type, the ZR and IAA high-starch type were higher before 80 DAP, after that it became opposite. And the GA3 changed not obviously different in two types during thickening, however it in high-starch sweet potato was higher than low-starch before 95 DAP, with tuberous root thickening proceeding, the changing tendency of GA3 content became contrary for the two types. For all varieties, only the very significant and negative relationship existed between commercial percentage and ZR content, and no notable relationship between other yield traits and hormones. As far as high-starch type was concerned, its ABA was very significantly and negatively related with tuberous root yield. And IAA/ABA did remarkably negative with commercial percentage. On the contrary obviously positive correlation occurred between GA3 and starch yield for the low-starch type. In general, that the ZR content became going up was not beneficial to big tuberous root formation, the ABA was disadvantageous to tuberous root yield of high-starch cultivar, and GA3 could make for increasing starch yield of low-starch variety.5. Physical and chemical controlling mode for high-yielding cultivation in different types of sweet potatoThe experiment, with orthogonal regression design, research the planting mode for three different types of cultivars (Yushu-2, Nanshu-88 and Yushu-10), whose growth and development were controlled by N fertilizer, K fertilizer and cutting branches. The results indicated that the equation about economic yield and starch yield of Yushu-2 was of significant regression, but the equation about biomass and commercial percentage was not significant for the total regression. For the low-starch type, such as Nanshu-88 and Yushu-10, their regression equations were not remarkable about all yield characteristics. Therefore under the circumstances of experimental controlling, different types of cultivars had discriminatory sensitivity to three factors. Through researching on the controlling effect of the factors, the measure, that cutting branches were not helpful to the three cultivars, would influence yield negatively. For dual-purpose cultivar Nanshu-88, fertilizing a small quantity of N fertilizer could help to improve biomass, and the economic yield could be obtained through fertilizing generous N and K fertilizer and cutting no branches. In addition, K fertilizer was beneficial to its commercial percentage while cutting branches could result in the starch yield declining. For the feeding cultivar, it was obvious that Yushu-10 especially demanded K fertilizer, which affected every yield trait significantly. At the same time the interactive effect was evident in fertilizing K and cutting branches. Therefore it was not advisable to cut or mow vines of sweet potato in reality. And also in terms of different cultivar, scientific planting sweet potato, high yield and good benefit could be achieved through physical and chemical controlling that based on adjusting measures to local conditions and varieties.
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