Comparison Research On Cold Resistance Of Four Rhododendron Hybridum Cultivars

As one of the world famous ornamental flower with high merchantability, Rhododendron hybridum has been one of the horticultural cultivars with the best quality,the longest florescence and the largest sales market. But the low temperature in winter becomes an important restrictive factor in their popularization and application for the poor low temperature resistance. And no report can be found about some extra substance on Rhododendron hybridum, which has been found to enhance low temperature resistance of some plants. To solve these two problems, in this study, four common Rhododendron hybridum cultivars,’Fenhong’、’Puhong’、’Meihong’ and ’Wucai’ were used as experimental materials, artificial low temperature stress and different concentration of SA were choosen as influencing factors to investigate the change of cold resistance indexes.This study evaluated the cold resistance of four Rhododendron hybridum cultivars with the methodology of morphology,combining with analysis of variance,multiple comparisons,correlation and membership function between indexes,and the analysis of the effect of SA treatment of Rhododendron hybridum cultivars, which provided a theoretical basis for screening the cold resistance cultivars and improving cold resistance of Rhododendron hybridum cultivars.The main results are as follows:1、The effect of low temperature stress on growth morphology of the four horticultural cultivars,’Fenhong’、’Puhong’、’Meihong’ and ’Wucai’does exist under0℃、3℃,5℃and10℃, and some difference of the degree of damage can be identified due to different temperature and cultivars.The injury made by the stress of0℃and3℃is stronger than that made by5℃and10℃,and a little small number of plants can recover after the elimination of0℃and3℃stress,although almost all can recover which endured5℃and10℃. From growth morphology of the four horticultural cultivars, cold resistance from strong to weak could be estimated as follows:’Fenhong’>’Wucai’>’Meihong’>’Puhong’.2, Under low temperature stress,the obvious trend can be found on relative conductivity, soluble protein, soluble sugar, proline, MDA, CAT activity, POD activity and SOD activity of the four horticultural cultivars,’Fenhong’,’Puhong’’Meihong’ and ’Wucai’.and the overall trend was upward. Compared with contrast, the relative conductivity, osmotic regulation substances, MDA and antioxidant enzyme changed distinctively after eight days stress.Analysis of variance showed that the accumulation of each index of four Rhododendron cultivars all reached significant difference among cultivars and temperature (P<0.05), and the change of cold tolerance of Rhododendron hybridum can be evalued nicely by using these indexes.Therefore,the results showed that all the indexes were suitable for the screening of the cold-tolerant cultivars.3, Under low temperature stress, with temperature decreasing and time prolonging, the Ci of ’Puhong’ and ’Meihong’ was on the rise, but the Ci of ’Wucai’ and ’Fenhong’ decreased, which indicated that the nonstomatal limitations were the key factors for the decrease of Pn of Puhong’ and ’Meihong’ and stomatal limitations were the key factors for the decrease of Pn of Fenhong’ and ’Wucai’. According to comprehensive evaluation results, the cold resistance of four cultivars from strong to weak was:’Meihong’>’Fenhong’>’Puhong’>’Wucai’, therefore we cannot well explain which has a greater effect on the decrease of photosynthesis, and it remains to be further studied; with temperature decreasing and time prolonging, the Tr, Pn and Gs overall showed a downward trend. Analysis of variance indicated that, after eight days of low temperature treatment, the gas exchange parameters of four cultivars had significant difference between different cultivars and temperature (P<0.05).4、Analysis of chlorophyll fluorescence parameters of four cultivars showed that QP, Fv/Fm and Yield decreased with stress temperature decreasing and time prolonging, the lower the temperature and the longer the time, the greater the degree. Analysis of variance showed that:QP reached very significant difference between different temperature (P<0.01), and under the same temperature, the QP difference between cultivars was significant (P<0.05); Fv/Fm had significant difference between the cultivars and temperature (P<0.05); there was no significant difference lied in Yield among the cultivars (P>0.05), but significant difference between temperature (P<0.05);as for NPQ,it showed a upward trend and reached very significant difference between temperature (P<0.01),but under the same temperature, the NPQ difference between cultivars was not significantly (P>0.05).5、By the principal component analysis from the16cold resistance indexes of Rhododendron hybridum,the results showed that the relative conductivity、soluble protein、soluble sugar、Ci、Tr、QP and NPQ can be choosed as comprehensive evaluation indexes of cold tolerancc,and the effects of the other indexes can be ignored.The subordinative function analysis showed that the cold resistance of four cultivars from strong to weak was:’Meihong’>’Fenhong’>’Puhong’>’Wucai’, the results were consistent with morphological observation under low temperature stress.6、SA addition had significant influence on cold resistance of Fenhong’ and ’Puhong’. But the ability of adjusting the physiological and biochemical responses of membrane lipid peroxidation, osmotic regulation substances, photosynthetic efficiency and chlorophyll fluorescence parameters would gradually decreased with stress temperature decreasing and time prolonging.7、From the subordinative function analysis on the main physiological and biochemical indexes of ’Fenhong’ and ’Puhong’treated witn five different concentration of SA,0.3mmol/LSA processing had the best effect on ’Fenhong’with D being1.671,which was9.934%higher than that of contrast.Howerer,1.5mmol/LSA processing had the best effect on ’Puhong’with D being1.544,which was16.178%higher than that of contrast.8、SA addition had better effect on ’Puhong’,and all the concentration of SA could improve the cold resisitance of ’Puhong’ except for0.5mmol/L. In accordance with the concentration from low to high, the growth of D were:9.330%,6.020%,16.178%,13.469%, but the D decreased under0.5mmol/LSA treatment,with a decreasing amplitude of3.311%.