| Watermelon is one of the most important economic crops in the world, and is one of the pillar industries and the advantage products in Hannan province. Aphis gossypii Glover is an important pest in the world and a major destructive pest on watermelon. It can influence the yield of watermelon and transfect some serious virus.Breeding and utilizing aphid-resistant varieties is recognized the most active, the most effective and the most economic management strategy at home and abroad. The study set up a suitable evaluation technology system and reference materials,and then further develop the genetic and resistant mechanism of the aphid resistance of watermelon.These provides the technology, theory and material foundation design innovation and utilization of watermelon breeding for resistance to aphid molecules. The results are in below:1. To screen the aphid-resistant watermelon varieties, the resistance of different watermelon varieties to Aphis gossypii was identified by the ratio of aphid number in greenhouse and the ratio of the highest aphid index (Ⅰ)and average aphid index(Ⅰ*) in the field. The results showed that Black Watermelon and Green Beauty were the most resistant to A.gossypii; Black Beauty and Whelan were resistant to A.gossypii; Green Stripe and Sweet Beauty were the most susceptible to A.gossypii.15cultivars such as Golden Beauty and Xiaoling were susceptible to A.gossypii. The results above will provide a suitable evaluation technology system and reference materials.2. The resistant cultivar Black Watermelon and the susceptible cultivar Green Stripe as the parents was crossed. Their offspring phenotype of F1showed high resistance to aphis.Among F2population, the rate of the resistant and susceptible was3:1by x2test.It indicated that the resistance of watermelon to aphid was controlled by a single dominant nuclear gene,and was genetic stability.3. The physical defense effect to aphis was studied.The results showed the stomataldensity, hair density and the wax content were significant positive correlation with aphis-resistance (P<0.05, the correlation coefficients were respectively0.9608,0.9071and 0.8992). The stomatal density, hair density and the wax content of resistance varieties were respectively403.04～532.58individuals/mm2,6.46～7.02individuals/mm2and1.40～2.57mg/g. The stomatal density, hair density and the wax content of susceptible varieties were respectively283.34～337.39individuals/mm2,5.02～5.88individuals/mm2and0.70～0.97mg/g, and there are significant difference between resistance cultivars and susceptible ones (P <0.05).There was no significant difference between aphis-resistance and leaf thickness or hair length.Therefore, leaf morphology including wax content, stomatal density and hair density could be useful characters to screen resistance varieties.The results showed the changes of Chlorophyll content, Net photosynthetic rate, transpiration rate, the maximal photochemical efficiency of PSⅡ(Fv/F/m), the potential photochemical efficiency of PS Ⅱ(Fv/Fo), effective photochemical quantum yield of PS Ⅱ(Y(Ⅱ)) and coefficient of photochemical fluorescence quenching(qP) after infection were significant correlation with aphid-resistance (P<0.05, the correlation coefficients were respectively0.8048,0.9482,0.9110,0.8936,0.8266,0.8932and0.8396). The Chlorophyll content, Net photosynthetic rate, transpiration rate, Fv/Fm, Fv/Fo, Y(Ⅱ) and qP of resitance varieties were respectively0.70～0.75,0.82～0.85,0.49～0.57,0.95～0.98,0.84～0.91,0.72～0.76,0.60～0.63times as those of the former.Those of susceptible varieties were respectively0.54～0.60,0.62～0.72,0.44～0.48,0.83～0.93,0.73～0.77,0.51～0.61,0.49～0.55times as those of the former, and there are significant difference between resistance cultivars and susceptible ones (P<0.05). There were no correlations between intercellular CO2concentration (Ci), stomatal conductance (Gs) and aphid-resistance. The damage to resistance varieties were much smaller than the resistance ones while the same situation appeared in photosynthesis and the blade PSII reaction center.4. The nutrition defense effect to aphis was studied.The results showed the contents of soluble nitrogen, free amino acids and proline were significant negative correlation with aphid-resistance (P<0.05, the correlation coefficients were respectively0.8858,0.9267,0.8671).Aphid-resistance were positive correlation with higher soluble sugar/nitrogen ratios (P<0.05, the correlation coefficient was0.9069). The contents of soluble nitrogen, free amino acids, proline and soluble sugar/nitrogen ratios of resistance were1.86～3.03mg/g,2.62～2.77mg/g,0.23～0.46mg/g and5.38～7.94. Those of susceptible varieties were respectively5.26～5.82mg/g,3.44～3.83mg/g,0.67～0.87mg/g and2.27～ 2.95, and there are significant difference between resistance cultivars and susceptible ones (P <0.05). There were no correlations between soluble sugar, vitamin C and aphid-resistance.Therefore, leaf nutrient including soluble nitrogen, free amino acids, proline and soluble sugar/nitrogen ratios could be useful characters screen resistance varieties.5. The defense effect of secondary metabolites to aphis was studied.The results showed the content changes of phenol, tannin were significant positive correlation with aphid-resistance (P<0.05, the correlation coefficient were respectively0.8947,0.7578). Aphid-resistance were negative correlation with the changes of MDA (P<0.05, the correlation coefficient was0.8946).The content of phenol, MDA, tannin of resitance varieties after aphid damage were respectively1.15～1.35,1.43～1.47,2.04-2.19times as those of the former, but those of susceptible ones were respectively0.65～0.73,1.92～2.21,0.37～1.03times as those of the former, and there was significant difference between resistance cultivars and susceptible ones (P<0.05)6. The defense effect of enzymology to aphis was studied. The results indicated the activity incresse of PPO, POD, CAT, SOD and ASA-POD after infection were significant positive correlation with aphid-resistance (P<0.05, the correlation coefficients were respectively0.8144,0.8054,0.7798,0.8693and0.8175). The activities of PPO, POD, CAT, SOD and ASA-POD of resitance varieties were respectively1.93～2.23,2.86～3.78,1.78～2.59,2.77～3.59and2.12～2.83times as those of the former, those of susceptible varieties were respectively1.00～1.18,1.12～1.19,1.03～1.13,1.05～1.21andl.14～1.18times as those of the former. There were significant difference between resistance cultivars and susceptible ones (P<0.05)7. Random Amplified Polymorphic DNA was employed to detect a molecular marker linked to resietant gene in watmelon cultivar. A mark W0453o from89random primer was proved to be linked aphid resistant gene by bulk segregating analysis (BSA) with F2population. WO4530was also tested with F2population,resistant and susceptible cultivars. According to the sequence of fragment analysis, one pair of primers had been designed. The RAPD marker was converted into a SCAR marker which was named WO4-S.The results will help us screen seed resource of resistance to Aphid, clone and analyze resistance genes. |
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