Studies On Low Temperature Tolerance And Downy Mildew Resistance Of Cucumber Inbred Lines And Their F₁ H=ybrids

Low temperature is the main limiting factor in cucumber production and downy mildew is a common disease in cucumber production.In this experiment,in order to identify materials with strong cold and downy mildew resistance,selection of cucumber inbred lines and their Fi hybrids by our group were used as test materials.The low temperature tolerance of cucumber was evaluated by the germination condition of cucumber under different indoor temperature and different sowing date in the field,and the regression equation of germination index on germination temperature was made.At the same time,Physiological and biochemical indexes and the morphological character of the materials were determined under the condition of suitable temperature,and the disease resistance of cucumber was identified by investigating the disease index after artificial inoculation in the field.The main findings are as follows:In laboratory identification,there were significant differences in germination rate and germination index of cucumber at different temperatures.In field identification,there were significant differences in seedling emergence rate and emergence index between different sowing dates.The 11 cucumber materials in our group could be divided into three grades by comprehensive analysis:The hybrids of Chang x Jin,Chang × Ning,Xin × Jin,Xin ×Ning and Shan × Jin were belonged to strong low temperature resistant materials;The hybrids of Shan × Ning,the lines of Changchun and Shandong were belonged to mid low temperature resistant materials;The lines of Xintai,Jinqi and Ningyang were belonged to weak low temperature resistant materials.The regression equation between germination index and germination temperature was gotten.The critical temperature of low temperature germination of 11 materials were found out.The critical temperature of low temperature germination of 6 cucumber hybrids was between 13.7-14.1 ?,the critical temperature of low temperature germination of 5 inbred lines was between 14.9-15.7 ?.The relationship between the content of related substances at the room temperature and low temperature resistance of the materials was determined.The SOD content of inbred lines was between 13.46-38.60 U.min-1ug-1protein.The SOD content of hybrids was between 39.52-50.63 U.min-1.ug-1 protein;The POD content of inbred lines was between 3.92-8.24 guaiacol.G-1FW.hr-1.The POD content of hybrid was 9.66-12.51 guaiacol.G-1FW.hr-1;The MDA content of inbred lines was 33.11-49.42umol.g-1,and the MDA content of hybrids was 21.60-43.65umol.g-1;The soluble protein content of inbred lines was 18.50-27.40 mg.g-1.The soluble protein content of hybrids ranged from 28.33 to 47.22 mg.g-1.The SOD activity and the POD activity and soluble protein content of the varieties with strong cold tolerance were higher than those with weak cold tolerance.The MDA content of the materials with strong low temperature tolerance was less than that of the medium and low temperature sensitive materials.The results showed that there was a positive correlation between the content of SOD activity,POD activity,MDA content and soluble protein and the cold tolerance of cucumber at room temperature.The chlorophyll A content,chlorophyll B content and chlorophyll content of inbred lines were 0.06-0.34mg.g-1,0.04-0.16mg.g-1,0.11-0.50mg.g-1,respectively.The chlorophyll A content,chlorophyll B content and chlorophyll content of hybrid were 0.03-0.34mg.g-1,0.02-0.07mg.g-1,0.06-0.41mg.g-1,respectively.The proline content of the inbred line was 37.73-49.87ug.g-1,and the proline content of the hybrid was 39.16-58.19ug.g-1.The soluble sugar content of inbred lines was 0.0143-0.0224ug.g-1,the souble sugar content of hybrid was 0.0141-0.0240ug.g-1.The chlorophyll content,proline content and soluble sugar content of inbred lines and hybrids had no obvious regularity in a certain range under normal temperature.This showed that there was no obvious relationship between chlorophyll content,proline content,soluble sugar content and low temperature tolerance.According to the disease index of cucumber after inoculation,the disease resistance grade of 11 materials in our group can be divided into the following four grades.The lines of Jinqi and the hybrids of Chang × Jin,Xin x Jin,Xin × Ning were belonged to resistant descendants;The lines of Ningyang and the hybrids of Chang x Ning,Shan x Jing,Shan x Ning were belonged to diseased-resistant materials;The lines of Shandong were belonged to medium sensing material;The lines of Changchun and Xintai were belonged to susceptible materials.There is a significant linear correlation between the disease index and the number of days after inoculation of various cucumber materials.5.The plant height,stem diameter,maximum leaf area and leaf number of each material showed an increasing trend with the advance of growth and development,and there were significant differences among the materials.Synthesis of four morphological traits showed the materials with strong resistance to low temperature and downy mildew have better growth and yield and the hybrids were generally superior to the inbred lines,but the growth and yield of the lines of Ningyang was prominent.There are significant differences between the single melon weight of each material and the total yield of the plot.The order of single melon weight of each material from high to low is the hybrids of Chang × Jin,the lines of Ningyang,the hybrids of Chang × Ning,the hybrids of Xin × Jin,the hybrids of Xin × Ning,the lines of Changchun,the hybrids of Shan × Jin,the lines of Jinqi,the hybrids of Shan × Ning,the lines of Xintai,the lines of Shandong.The total output of each material is in turn from high to low is the lines of Ningyang,the hybrids of Chang × Jin,the hybrids of Chang × Ning,the hybrids of Xin × Jin,the hybrids of Xin ×Ning,the hybrids of Shan × Ning,the hybrids of Shan × Jin,the lines of Changchun,the lines of Xintai,the lines of Shandong,the lines of Jinqi.