Effects of leaf thickness and trichome density of grapes on their resistance to Apolygus lucorum

Abstract: 【Objective】Grapes are one of the important fruits in China. In recent years, the damage byApolygus lucorum is increasing year after year, which results in the reduction of the quality and also decreases of production and leads to greater economic losses. Therefore, it is necessary to study the grape va⁃rieties resistance to A. lucorum. It is also necessary to evaluate the resistance levels of different grape vari⁃eties to A. lucorum. We must make clear the relationship between the leaf thickness, leaf upper epidermisthickness, leaf abaxial epidermis thickness, filamentous trichomes density, spinous trichomes density ofdifferent grape varieties and their resistance to A. lucorum.【Methods】We investigated the damage causedby A. lucorum on 9 grape varieties in the field during 2012—2014, and calculated the damage indexes ac⁃cording to the results obtained. The leaf damage level can be divided into 0, 1, 2, 3, corresponding to 0, 0-20%, 20%-40% and 40%-100% of the total leaf area, respectively. The resistance value of each year wasset as 1 to 5 and the damage indexes ranged from larger than 20% to smaller than 20%. We then averagedthe resistance values of three years to determine the resistance index. The resistance indexes ≤2 were thelow resistance varieties, 2-3 were moderate sensitive varieties, 3-4 were moderate resistance varieties,and ＞4 were high resistance varieties. The grape leaves used were the third leaf of each new shoot at theshoot-growing stage. By making temporary slides, we measured the leaf thickness, leaf upper epidermisthickness and leaf abaxial epidermis thickness under 400 times magnification in a laboratory microscope.The number of filamentous trichomes, with a density of 1 cm on the midrib of the grape leaves, was count⁃ed at 40 times magnification under a microscope. The spinous trichomes were distributed on the back ofgrape leaves. The spinous trichomes density was divided into 5 levels from low to high. We observed thespinous trichomes density at 100 times magnification under a microscope. All data were analyzed by usingDPS 9.50 statistical software. Multiple comparisons of damage index, leaf thickness and trichome densitywere analyzed using Duncan’s methods. The relationship between the leaf thickness, leaf upper epidermisthickness, leaf abaxial epidermis thickness, filamentous trichomes density, spinous trichomes density ofdifferent grape varieties and their resistance to A. lucorum were analyzed by using the liner regressionmethod.【Results】The resistance levels of the different grape varieties was obviously different (P＜0.05).The resistance indexes of‘Red Globe’‘Muscat Hamburg’‘Kyoho’‘Cabernet Sauvignon’‘CabernetFranc’‘Ruby’‘Cabernet Gernischt’‘Fujiminori’‘Chardonnay’were 1.33, 1.33, 2.00, 2.33, 2.33, 2.67,2.67, 4.33, 4.33, respectively.‘Fujiminori’and‘Chardonnay’had high resistance to A. lucorum (resis⁃tance index＞4).‘Red Globe’‘Muscat Hamburg’and‘Kyoho’had low resistance to A. lucorum (resis⁃tance index≤2). The leaf thickness, leaf upper epidermis thickness and leaf abaxial epidermis thicknessof different grape varieties were significantly different (P＜0.05). The maximum of leaf thickness, leaf up⁃per epidermis thickness and leaf abaxial epidermis thickness of grape varieties was with‘Kyoho’, whichwas 435.26, 65.60 and 39.87 μm. The minimum of the leaf thickness, leaf upper epidermis thickness andleaf abaxial epidermis thickness was with‘Muscat Hamburg’‘Cabernet Sauvignon’and‘Fujiminori’,which were 358.44, 49.37 and 31.24 μm, respectively. The filamentous trichomes density and spinous tri⁃chomes density of the grape leaves were found to be different among the various varieties (P＜0.05). Theleaves of‘Red Globe’and‘Ruby’were smooth and hairless, their filamentous trichomes density werelowest.‘Kyoho’‘Muscat Hamburg’and‘Cabernet Sauvignon’had the highest filamentous trichomesdensities. The number of filamentous trichomes per cm of‘Kyoho’‘Muscat Hamburg’‘Red Globe’‘Ru⁃by’‘Fujiminori’‘Cabernet Sauvignon’‘Cabernet Gernischt’‘Chardonnay’and‘Cabernet Franc’were6.60, 252.67, 18.87, 37.33, 10.87, 32.12, 137.73, 16.20, 40.07, respectively. The spinous trichomes densi⁃ty of‘Muscat Hamburg’was significantly higher than other grape varieties (p＜0.05). Through linear re⁃gression analysis, we found there were no significant correlations between the leaf thickness, leaf upperepidermis thickness, leaf abaxial epidermis thickness and their resistance to A. lucorum (y=-1.935 8+0.011 8x，R²=0.080 1，P=0.460 6；y=-1.358+0.070 3x，R²=0.131 1，P=0.338 3；y=9.536 3-0.202 3x，R2=0.239 0，P=0.181 7), and the filamentous trichomes density and spinous trichomes density showed nonsignificantcorrelations with the grape resistance to A. lucorum (y=2.861 3-0.081 1x，R²=0.014 9，P=0.7547；y=2.938 9-0.005 7x，R²=0.177 3，P=0.259 1).【Conclusion】‘Fujiminori’and‘Chardonnay’had thehighest resistance levels to A. lucorum, and‘Red Globe’and‘Muscat Hamburg’had the lowest resis⁃tance levels to A. lucorum. The leaf thickness, leaf upper epidermis thickness, leaf abaxial epidermisthickness, filamentous trichomes density and spinous trichomes density of the different grape varietieswere shown to have significant differences. There were no significant correlations between the leaf thick⁃ness, leaf upper epidermis thickness, leaf abaxial epidermis thickness and their resistance to A. lucorum.The filamentous trichomes density and spinous trichomes density had no significant correlations with thegrape’s resistance to A. lucorum.