Difference In Resistance Of Tea Plant Cultivars Against Tea Green Leafhopper And Disparity Of Quality Of Their Steamed Teas After Leafhopper Damaged

The tea green leafhopper,Empoasca vitis G?the,is one of the most important pests in the Chinese tea growing area,which results in the obvious reduction of output and deterioration of quality of teas year after year.Breading and extending the resistant cultivars are beneficial to restraining the leafhopper’s population and cutting down the application amount of insecticides.In order to investigate the potential for tea plant against the leafhopper,eleven national grade of elite cultivars and local characteristic cultivars were chosen out,on which the feeding behaviors of the leafhopper was recorded and prepared according to the detection of Electrical penetration graphy(EPG).The recorded data were analysed by cluster analysis to assess the resistant grades of the eleven cultivars.Cultivars Zijuan,Zhongcha 108 and Wuniuzao were respectively screened as the resistant,middling resistant and susceptible cultivar.The leafhopper-damaged fresh leaves of every cultivar was processed into the steamed tea samples,with the steamed tea samples processed from the intact fresh leaves as CK.The taste,the aroma and the soup color of the three resistant grades of samples and CK sample were respectively detected by electronic tongue,electronic nose and colorimeter.The data acquired were analized to disclose the difference in the potential for the three tea plant cultivars against the leafhopper and explain the difference among the damaged degree of the steamed tea samples of resistant and susceptible cultivars by the leafhopper.The main results as follows.Part 1: Resistance/Susceptibility of 11 Tea Plant Cultivars to the Tea Green Leafhopper Determined by EPG Technique and Its Correlation with the Defensive Substances in the Tea Leaves: Using EPG technology to detect the probing behavior of E.vitis on 11 varieties of tea plants and judge resistance,main components of tea was detected by HPLC and analyze the correlation betweenresistance and chemical composition.Result showed that:(1)7 distinct EPG waveform and its possible biological significance had been cleared,namely,Np,A,S,C,E,F and R wave,the characteristics and rules of various waveform was analysed.E,F and uncertain biological significance R were resistant-related wave;(2)During the test period of 5 h,probe numbers of E.vitis on Huangguanyin and Longjing 43 were the most,followed by Zijuan Ningbohuangjinya and Jinguanyin,Tieguanyin and Anjibaicha were the least.Averageduration ofE on Tieguanyin and Huangmudan were the longest,followed by Wuniuzao and Anjibaicha,Zijuan was the shortest.The average duration of F on Huangguanyin wasthe longest,followed byLongjing 43 and Ningbohuangjinya,Jinguanyin was the shortest;(3)The 11 tea cultivars were claasified into two groups with cluster analysis,based on the three major parameters which were probe number,E,F.The firet class included six cultivars,Anjibaicha,Wuniuzao,Zimudan,Zhongcha 108,Huangmudan and Tieguanyin;and the second were Zijuan,Longjing43,Ningbohuangjinya,Huangguanyin and Jinguanyin.The resistance of the second class was stronger than the first class;(4)From susceptiblevarieties to resistant varieties,catechins content increased significantly,and the correlation between total catechins and the duration of E was significantly negative(P < 0.05).Caffeine,amino acids and soluble sugar content were not related with the resistance-susceptiblility.Part 2: Disparity in taste,aroma and color between leafhopper damaged and intact tea samples by means of techniques of electronic tongue and electronic nose and colorimeter: In order to investigate the effect of the damage from tea green leafhopper on taste,aroma and color of merchant teas as well as the disparity in the resistance of different cultivars against the leafhopper,Pest damage affected the physiological metabolism of tea foliage,which resulted in changes in taste,volatiles and soup color of tea.In order to investigate the influnce of the leafhopper damaging on tea physiology,the cultivars Zijuan,Zhongcha 108 and Wuniuzao,which respectively occupied resistance,middling-resistance and susceptibility to the tea green leafhopper,were chosen.Tested tea plants of each of the three cultivars were introduced by the same number of the leafhoppers and damaged for 0 h,12 h,24 h,36 h,48 h and 60 h respectively.After being damaged,the leaves were pluckedand processed into the steamed tea samples,the taste and thearoma of whose soup was respectively detected by electronic tongue and electronic nose.Subsequently the acquired data were analized by the principal component analysis(PCA)and the soft independent modeling of class analogy(SIMCA).Then used colorimeter to detect change in color of the tea soups of the series of the steamed tea samples.It was found out that electronic tongue and electronic nose could be applied for discriminating intact tea leaves from pest-damaged tea leaves,making a distinction among tea leaves with different damaged time,and differentiating cultivars with resistance and susceptibility to the leafhopper.The colorimeter revealed that as for the steamed tea samples damaged from 0 h to 60 h,the chroma of yellow-green of tea soups of cultivars Zijuan and Wuniuzao deepened,and the brightness of tea soup of cultivar Zhongcha 108 obviously fell.It was considered that: The duration of E,F and probe number can be used as main parameters on tea plants of resistance-susceptiblility.R may be associated with phloem feeding resistance,still needs further research.Catechin is the material related to resistance.The leafhoppers’ s damaging markedly altered the taste of tea soup,and the changes in the taste became obvious while the damaging time prolonged.The transformation in flavouring materials were responsible for the tea soup chroma deepened and the brightness declined.As the extension of leafhopper damaging time,the taste and aroma and colour of steamed tea samples of the resistant cultivar Zijuan varied slightly more regularly than other two cultivar.The research work provided reference todeeply inquire intothe mechanism of insect-resistant of tea plants,and offered evidence to evaluation for tea samples damaged by diseases and pests.