Drought Resistance Evaluation Of Six Newly Introduced Rhododendron Varieties

Rhododendron is one of the most important ornamental plants in the application of landscaping because of its diversity of flowers and varieties.There are few varieties of Rhododendron used in Fuzhou greening.It has no drought resistance,and the climate drought often occurs in Fuzhou area because of the uneven seasonal precipitation,which seriously affects the normal growth and development of Rhododendron and its popularization and application.In order to solve the single cultivated variety of Rhododendron and difficult to adapt to the drought climate in the local area,we hope to choose the varieties with good ornamental and drought resistance to promote the landscaping of Fuzhou.This study selects six Rhododendron varieties(’Ziqidongsheng’,’Zixiu’,’Xueqing’,’Shenzhouqi’,’Hongyang’ and ’Royal Wing’)as experimental materials from the Rhododendron varieties introduced by the garden Bureau to study the effects of PEG-6000 on physiological and biochemical indexes of Rhododendron leaves under different drought stress.The membership function method was used to evaluate the drought-resistance of six varieties,and the varieties with strong drought-resistance were selected for promotion and application.The application of Rhododendron in urban greening of Fuzhou city was investigated.The results show that:(1)The application of Rhododendron in the greening of Fuzhou city is mainly green hedgerow.The main cultivar is R.pulchrum Sweet,and the color is mainly purple red.There are some problems such as lack of varieties,single configuration and color,small area of road greening,poor growth.It is suggested to pay attention to the introduction of new varieties,strengthen the research on resistance and adaptability,select varieties with strong stress resistance for popularization and application,and strengthen the maintenance of Rhododendrons,scientific management and reasonable allocation.(2)PEG-6000 has high molecular weight,can not be absorbed by cells and produce toxicity to plants.lt has good hydrophilicity.The water potential of solution is inversely proportional to the amount of PEG added at a certain temperature.It is a common osmotic regulator for simulating drought.With the increase of stress time,the leaves of Rhododendron withered first and then withered gradually,accompanied by leaf shedding.With the increase of water stress time,the leaf blight of ’Ziqidongsheng’ and ’Xueqing’ appeared late,which was stronger under the same time of drought treatment.Under different drought treatments,’Ziqidongsheng’ had the longest half-lethal time,followed by ’Xueqing’,’Shenzhouqi’,and ’Hongyang’,’Zixiu’ and ’Royal Wing’ had the shortest half-lethal time.(3)Under the drought stress of PEG,with the increase of stress time and degree,the relative conductivity and MDA content of six Rhododendron varieties significant increase gradually(P<0.05),and the increase was obvious in the later period,and the maximum value occurred at the treatment of 48 h.Among the six cultivars,the relative conductivity and MDA content of ’Shenzhouqi’ increased relatively small,while that of ’Royal Wing’ increased relatively large.(4)Under the drought stress of PEG,the chlorophyll a,chlorophyll b,total chlorophyll content,chlorophyll a/b,Y(Ⅱ),qP,NPQ and ETR in six Rhododendron varieties were first increased,then decreased or gradually decreased with the increase of water stress time,there was significant different(P<0.05).Chlorophyll content of ’Zixiu’,’Hongyang’ and ’Royal Wing’ decreased rapidly in the late stage of stress.Y(Ⅱ),qP and ETR of ’Royal Wing’ decreased during the period of stress,and the ’Hongyang’ and ’Zixiu’ declined significantly in the later stage of the stress.(5)Under drought stress,SOD activity of six Rhododendrons increased first,then decreased or gradually decreased with the deepening of stress degree and the extension of stress time,showing a significant difference(P<0.05).The SOD activity of ’Ziqidongsheng’ and’Xueqing’ increased,while ’Zixiu’ and ’Royal wing’ decreased obviously.During the stress period,soluble protein and proline content gradually increased or first increased and then decreased,and soluble protein content in all cultivars showed significant changes(P<0.05).Besides ’Zixiu’,proline content in other cultivars also showed significant changes(P<0.05).The content of soluble protein and proline in ’Xueqing’ increased significantly,the content of soluble protein in ’Royal wing’ increased slightly,and the content of proline in’Zixiu’ decreased significantly at the later stage of stress.(6)Using the relative conductivity,MDA content,chlorophyll a,chlorophyll b,total chlorophyll content,chlorophyll a/b,Y(II),qP,NPQ,ETR,SOD activity,soluble protein and proline content,etc.13 indexes to comprehensive evaluation of drought resistance of the six Rhododendron varieties through the method of subordinate function.The drought resistance ranking of six varieties is:’Ziqidongsheng’>’Xueqing’>’shenzhou’>’Royal wing’>’Hongyang’>’Zixiu’.The results were consistent with plant morphological changes under drought stress.