Resistance Mechanisms Of Tea Plant Cultivars To Tea Green Leafhopper

Tea green leafhopper Empoasca vitis G the (Hemiptera: Cicadellidae), is an importantpest of tea plant in China, and seriously affect the tea quality and yield. Because the eggs werelaid in plant tissues, chemical pesticide applications usually fail to achieve the desired result.Standing on the piont of view of variety resistance, the tea cultivars were grouped basing onthe results of leafhopper’s field population density, life cycle duration, adult reproduction, etc..Secondly, resistance factors location of tea cultivars were achieved through the study ofleafhopper’s feeding behavior on different cultivars, which was investgited by electricalpenetration graph (EPG) technique. Based on these results, the morphology, anatomicalstucture and biochemical compositions of different tea cultivars were analyzed, as for thecompositions with significantly different content between resistant and susceptible cultivars,the bioassay experiment were then carried out to determine the resistance factors and theresistance mechanism in resistant tea cultivars. The main results are as follows:1. The eight tea cultivars including En biao (EB), Zhu shan1(ZS), Lan tian (LT), Banzhu yuan (BZY), Chang xing zi sun (CX), Ju yan (JY), Jian de (JD) and De qing (DQ) wereselected for the further study according to the results of hatched nymph number from the fieldtea shoots, hatched nymph number from the artificially infested tea shoots and fieldpopulation density on12tea cultivars such as TT etc.2. Life cycle duration, nymph number from per female and nymph survival rate of E.vitis on the eight tea cultivars were investigated, and two groups were classified according towhich results. Ⅰ: resistant group including JY, DQ, JD and CX, which were resistant to E.vitis; Ⅱ: susceptible group including LT, BZY, ZS and EB, which were susceptible to E. vitis.JY is the most resistant to E. vitis and EB is the most susceptible to E. vitis in the eight teacultivars.3. The feeding behaviors of E. vitis on tea plant were identified by using planthistological and insect behavioral mothods, which including EPG, transmission electronicmicroscope and other techniques. Thus the result firstly comfirmed that E. vitis blongs to cellrupture feeder. Seven EPG waveforms were produced by E. vitis on tea plant, the mainwaveforms Np, E1, E2and E3were correlated with stylet non-probing, channel-cutting and multiple-cell laceration, mesophyll active ingestion and vascular active ingestion, respectively.The whole process of a probe was used to performing as Np-E1-E2-E3-E1-Np.4. The result of EPG non-sequential parameters analysis showed that the ingestiondurations of E. vitis on susceptible cultivars are longer than resistant cultivars, although onlyEB and ZS were significantly longer than all of resistant cultivars. On the other hand, EPGsequential parameters caculation showed that the surface resistance was existed on CX, DQand JD, but this resistance was absent from LT; the epidermis-mesophyll of JY, JD and DQshowed resistace to E. vitis, but all of the four susceptible cultivars were lack of the resistance;the mesophyll tissue of JY, CX and JD were resistant to E. vitis, but this resistance have notbeen discovered in BZY and EB.5. In morphology, the difference between resistant and susceptible cultivars wasdiscovered in new tea shoots color (resistant cultivars showed darker than susceptiblecultivars), length of new tea shoots with one bud and three leaves (resistant cultivars＜susceptible cultivars), leaves size (resistant cultivars＜susceptible cultivars), leaveshardness (resistant cultivars＞susceptible cultivars) and extension of leaf body. As forphysical structure, the trichome length and density of leaves of resistant cultivars weresignificantly higher than of susceptible ones; all resistant cultivals had significantly higherwax content than susceptible cultivars except EB. Additionally, lower epidermal thickness ofresistant cultivars were higher than that of susceptible ones. For the biochemical compositions,the content of tea polyphenols and chlorogenic acid in resistant cultivars were significantlylower than susceptible cultivars. On the contrary, the content of γ-aminobutyric acid inresistant cultivars was obviously higher than that of susceptible cultivars; theanine content inDQ, JY and CX was significantly lower than all susceptible cultivars; moreover, the contentof aspartic acid of resistant cultivars was lower than all susceptible cultivars, although thevalues of resistant cultivars and two susceptible cultivars ZS and BZY reached significantlevel.6. Correlations of physical and chemical data of tea cultivars with life cycle duration andnymph number of each female of E. vitis were analyzed. The result showed that trichomelength and density, wax content and γ-aminobutyric acid content were negatively correlatedwith the nymph number from per female, this correlation reached highly significant level; leaflower epidermal thickness showed significantly negative correlation with the nymph numberfrom per female, but content of tea polyphenols was positively correlated to it. On the otherhand, trichome length and density and leaf lower epidermal thickness showed significantlypositive correlation with life cycle duration of E. vitis. Contrarily, the significantly negativecorrelation was discovered between the content of tea polyphenols and life cycle duration of E. vitis.7. Artificial diets were made for the biaassay analysis of γ-aminobutyric acid. Theinhibition role was discovered in high concentration of tea polyphenols on growth andsurvival rate of E. vitis, which was inconsistent with the previous result of correlation analysis.High concentration of γ-aminobutyric acid had a negative impact on the growth and thesurvival rate of E. vitis. Although chlorogenic acid has not been found any certain correlationwith the survival rate of E. vitis, the duration of1stand2ndinstar of E. vitis were graduallyincreased with the increase of the content of chlorogenic acid in diet. Additionally, althoughaspartic acid was not related to tea resistance, the duration of1stand2ndinstar of E. vitis wasshortened with the concentration increasing; the survive and development of E. vitis have notbeen influenced by the changes of concentration of theanine.8. Different tea cultivars have different resistance mechanisms to E.vitis. The surfaceresistance was determined by wax content, trichome length and density. Thickness of thelower epidermis was the important reason for epidermis-mesophyll layer resistance.Biochemical components may be the main determinant of the mesophyll resistance. Moreover,the chemical resistance was the key role for determining the resistance level of tea cultivars toE. vitis, γ-aminobutyric acid may be one of the key factors of the chemical resistance.