Studies On Growth And Some Physiological And Senescence Characters In Different Cassava Varieties

The characters in agronomy, yield, quality, gas exchange, photosynthetic metabolism, photosynthate allocation, nitrogen metabolism and senescence in five cassava varieties, SC124, GR911, Baxizhong and GR891 and Nanyanghong , were compared with the later as the control. The results were as follows.For the characters related to the agronomy, yield and quality, GR911 and SC124 emerged fastest with the highest gemination rate of 100%, and GR891 showed the lowest germination rate of 42.2%. GR911 grew fastest, and SC124 and GR891 the most slowly. The order of the theoretical earthnut yield per unit area was GR911> SC124>GR891> Nanyanghong > Baxizhong. And that of starch content was Baxizhong >GR891>GR911> Nanyanghong.For the gas exchange characteristics, all the cassava varieties showed the highest net photosynthetic rate in June and descended with growth since then, and that in the control showed the lowest although different varieties behaved veried. There were highly significant and positive correlations between any two of the indexes of stomata conductance, intercellular CO2 concentration, transpiration rate and net photosynthesis rate. The correlation between intercellular CO2 concentration and net photosynthetic rate was the highest with the correlation coefficient of 0.8388**, followed by that between transpiration rate and photosynthetic rate.For the characters related to the photosynthate allocations, the leaves of cassava accumulated and deposited sucrose and starch from assimilation in the chloroplasts and cytoplasm. The earthnut starch of cassava accumulated mostly depending on the sucrose transferred from the leaves from July to August; but depending on the invertion of starch deposited in the leaves after September.For the characters related to the nitrogen metabolism, the correlation coefficient between NRA and soluble protein content was not significant in cassava.For the characters related to the photosynthetic metabolism, during the fast growing period, the total chlorophyll content and the activities of GO, Hill reaction, photophosphorylation and ATPase kept at high levels, and descend with the senescence of plants, and they showed the lowest in the control. The correlations between net photosynthetic rate and photophosphorylation and Ca2+-ATPase activity were significant and positive, that between net photosynthetic rate and GO activity was highly significant and positive.During senescence of cassava, the POD activity were constantly increased; the CAT activity descended a little; the SOD activity and MAD content went up at the beginning of the senescence, and then went down. The correlation between MAD content and SOD activity was significant and positive. Based on the performances of the activities of POD, CAT and the content of MAD in different cassava varieties, Baxizhong and GR891 showed the strongest resistant ability to senescence, and SC124 and Nanyanghong medium, and GR911 the weakest.For evaluation of the tested varieties based on the comprehensive performance, the varieties GR911 and SC124 show the best, GR891 medium, and Baxizhong the worst.