Identification Of Tobacco Resistance To Bacterial Wilt In The Field And Study Of Identification Method At Seeding Stage

Tobacco bacterial wilt(TBW)is a bacterial disease caused by Ralstonia solanacearum,which has seriously affected tobacco yield and quality.Breeding and planting disease-resistant varieties is a fundamental way to control the occurrence and prevalence of TBW,and screening and identification of resistant materials is very important for resistance breeding.In this study,the TBW resistance of 186(133+21+32)tobacco accessions in the field was evaluated based on disease index,and the results of the resistance ranking were statistically tested and corrected.Meanwhile,using the days for the first seedling to be diseased after inoculation(D1),the days for half of the seedlings to be diseased after inoculation(D50),the days for all seedlings to be diseased after inoculation(D100)and wilt index as the indicator of resistance,we screened out suitable bacterial concentrations that can distinguish well the resistance of three species(lines)at this seedling age,the four-leaf tobacco seedlings of three tobacco varieties(lines)with significant differences in resistance(performance in field)were used as materials.After that,4-leaf tobacco seedlings of 66 tobacco accessions(all from the above field test)were inoculated by direct irrigate method using the suitable bacterial concentration.The resistance index(D1,D50,and D100)were observed and recorded and the wilting index was calculated.The correlation analysis between the seedling resistance index(D1,D50,and D100,wilt index)and the field disease index was applied to determine the appropriate resistance index;Regression analysis of wilting index in the seeding stage and disease index in the field was applied to determine the seedling resistance evaluation criteria and the seedling resistance of 66 tobacco accessions-was-evaluated according to this standard.The results were as follows:1.Identification of the TBW resistance in the field of 133 tobacco accessions from Qingzhou Tobacco Research Institute of China showed that 39 accessions were resistant,73 mid-resistant,20 mid-susceptible and 1 susceptible.Statistical tests confirmed the reliability of 6 resistant and 6 mid-resistant accessions and corrected the resistance ranks of the other accessions.2.Identification of the TBW resistance of 21 tobacco accessions from Fujian Province showed that 4 accessions were resistant,3 mid-resistant,6 mid-susceptible and 8 susceptible.Statistical tests confirmed the reliability of 1 resistant,1 mid-resistant and 3 susceptible accessions and corrected the resistance ranks of the other accessions.3.Identification of the TBW resistance of 32 tobacco accessions from all over the country showed that 4 accessions were resistant,16 mid-resistant,11 mid-susceptible and 1 susceptible.Statistical tests confirmed the reliability of 4 mid-susceptible and 1 mid-resistant accessions and corrected the resistance ranks of the other accessions.4.The results of bacterial strain concentration screening showed that all of the three concentrations could distinguish the resistance among the varieties.To save the experiment time,the concentration 106 cfu/ml could be adopted.5.The correlation analysis of resistance index at seedling stage and disease index in the field of 66 accessions showed that:D1,D50,and D100were significantly negatively correlated with disease index,while the wilting index was significantly positively correlated with disease index.Moreover,the correlation coefficient between the wilting index and the disease index was the highest.6.Regression analysis showed that there was a significant linear relationship between the wilting index at seedling stage and disease index in the field,and the linear equation was:Y=0.645X+33.4.According to this linear equation,the criteria for resistance ranking based on wilt index corresponding to disease index was formed:I:0-33.4;R:33.5-46.3;MR:46.4-59.2;MS:59.3-72.1;S:72.2-85;HS:85.1-97.9?7.The resistance ranks of 66 tobacco accessions at seedling stage were evaluated.The results showed that 20 accessions were resistant,21 were mid-resistant,18 were mid-susceptible and 7 were susceptible.The results of resistance ranking at seedling stage were basically the same as those based on the field trials except for 7 accessions.It is indicated that the seedling resistance identification method of this experiment(The four-leaf tobacco seedlings were inoculated with the bacteria solution of 1×106 cfu/ml concentration by directly watering root method.The wilting index was used as a resistance index,and the resistance was evaluated using the seedling resistance classification criteria.)was feasible.This result will facilitate the identification of bacterial wilt resistance of large amount of tobacco accessions.