| Fusarium wilt is a serious threat to the production of watermelon worldwide soil-borne diseases,with the expansion of the protected cultivation area,continuous cropping caused a large area of occurrence of Fusarium wilt,breeding and screening resistant graft rootstock is the effective way to solve watermelon wilt,watermelon is very sensitive to low temperature,it belongs to thermophilic crop,protected cultivation is based on both early spring and late autumn in most parts of northern China,winter and spring temperature are low,low temperature affects the growth and development of protected cultivation watermelon,restricting the improvement of watermelon production and quality.To adapt to the environment of protected cultivation in northern,screening resistant wilt and high chilling tolerance watermelon graft rootstock has important practical significance to research Fusarium wilt resistance identification of watermelon rootstock,cold tolerance evaluation of rootstock and cold tolerance physiological mechanism of rootstock seedlings.Spore suspension inoculating artificially was used to identify 39 rootstock materials for resistance to Fusarium oxysporum f.sp.niveum,three excellent resistant rootstocks were screened to study effects of low temperature treatment on seedling growth,leaves physiological characteristics and nutrient absorption characteristics of seedling root.To explore low temperature adaptability and cold tolerance physiological mechanism of watermelon resistant rootstocks,clarify the absorption rules of N,P and K of seedling roots under low temperature,providing a theoretical basis for the cold tolerance evaluation of watermelon resistant rootstocks and nutrient scientific management in protected watermelon cultivation.The results were as followings:1.The experiment found that it is race1 of Fusarium oxysporum f.sp.niveum.Among 39 materials that were screened for resistance to Fusarium oxysporum f.sp.niveum,4 pieces were resistance,which accounting for 10.3% of the total tested materials,25 pieces are moderate resistance,accounting for 64.1%,10 pieces are light resistance,accounting for 25.6%,but none was found for immunization or complete susceptibility.2.The growth of seedlings was significantly inhibited under low temperature stress,chilling rate and chilling injury index increased significantly,the absolute increment of plant height,stem diameter,leaf area and leaf number,total dry matter accumulation and distribution were significantly decreased.The cross 'BEH×Ag2-1' showed significantly the least chilling index and morphological change than 'BYH×FR328' which demonstred less chilling injury than 'BEH×FR328' significantly.3.Low temperature significantly decreased photosynthetic ability of resistant rootstocks leaves.The content of Chl(a+b)and Car,Chla/Chlb,Pn,Tr,Gs,WUE and Ls of three rootstocks leaves were significantly decreased by low temperature,Ci was significantly increased,non-stomatal limitation is main cause of photosynthetic decline,the Fv/Fm,Fv/Fo,Y(?),ETR and q P of rootstocks leaves were significantly decreased,the NPQ of 'BEH×FR328' leaves was significantly decreased,but other rootstocks had increasing trend.The 'BEH×Ag2-1' showed significantly higher efficiency of absorption and utilization light and electron transport than others,the photosynthetic apparatus of 'BEH×FR328' leaves was destroyed and damage of photosynthetic activity was most severely.4.Low temperature stress destroyed the membrane integrity of three watermelon resistant rootstocks,started the antioxidant enzyme system and increased the osmotic adjustment content.The relative conductivity,MDA,soluble sugar,soluble protein and proline content,SOD,POD and CAT activities of rootstocks leaves were significantly increased by low temperature.The increase of antioxidant enzyme activity and osmotic adjustment substance increased the cold tolerance of plants,which was an important physiological mechanism of watermelon resistant rootstocks against low temperature.5.The growth of three resistant rootstocks root was significantly inhibited by low temperature.The root length,root volume,root activity,root total and active absorption area were significantly decreased,the above-mentioned root index of cold tolerance rootstock 'BEH×Ag2-1'showed significantly than medium patience and low temperature sensitive rootstocks,the N,P and K contents of stems leaves and the N,P contents of resistant rootstocks root were significantly decreased by low temperature,indicating that the low temperature reduced the plant root activity and inhibited the absorption of N,P and K elements.Under 10?/5?,the cold tolerance rootstock showed significantly higher N,P and K contents of seedling than low temperature sensitive rootstock. |
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