| Rubber is a kind of renewable and strategic resources, which with oil, coal and steel were singled out as the fourth-largest industrial raw materials. China is the first majority consumers and the importing country of natural rubber. The development of natural rubber industry has far from enough to satisfy demand of construction of national security. However, with the rapid development of the natural rubber industry, the problem of dangerous mites widespread and damage situation also become seriously, which has become one of the important factors that restricted natural rubber industry. The six-spotted spider mite (Eotetranychus sexmaculatus) is one of the most important pests in rubber tree, and recently, the harm caused by the mite becoming more and more serious. The mite feeds on plant juices and causes leaf yellowing as well as discoloration is brown to purple, which mainly affects the light reaction process and inhibits the effects of photosynthesis. As a result of the mite damage seriously, the rubber tree stops growing and stops making latex and the yield would be reduced destructively. If young rubber trees have been seriously damaged, twigs will slowly become dry and dead finally. For a long time, pesticides are the main control method against E. sexmaculatus, however, pesticides also bring the problems of environment pollution and serious "3R" problem. Host plant resistance have been considered as the most active, effective and economic measures against insects and mites, and has already become directional measure for pests control both at home and abroad. In view of the situation that there’s no definitive mite-resistant rubber gernplasms at home and abroad so far, and lack of systematic research theory and technical support of mite-resistant rubber germplasms. Furthermore, according to the development and the actual needs of the modern natural rubber industry, after establishing the mite-resistant evaluation criteria of rubber germplasms and obtaining the stable resistant and susceptible rubber germplsms, this study compared the difference of development, reproduction and the protective enzyme activities of E. sexmaculatus feeding on resistant and susceptible rubber tree leaves. The difference of nutrients, secondary metabolites products contents and the activities of protective enzymes (PPO, POD, CAT, SOD, AsA-POD, a-NA EST andβ-NA EST) in leaves damaged by the mite were also be compared with the key point of interaction mechanism between pest mite and the host plant, so that we can elucidate the mite-resistant mechanism of rubber germplasms, and at the same time, provide basic information, experimental material, theory and technical support for the molecular design breeding in mite-resistant rubber germplasms. The main results are as follows:1. Five germplasms steadily developed resistance to E. sexmaculatus, IRCI12, Reyan87-6-5, IAN717, RRIM600, RRIC52, and five susceptible germplasms, Guiyan77-11-23, IAN2904, IAN2887, RRII103, and RRII105were screened from24rubber core germplasms on the basis of the established mite-resistant evaluation criteria of rubber germplasms. It provided experimental material and technical support for the resistant breeding of rubber germplasms. 2. The development and the reproduction of E. sexmaculatus fed on the resistant germplasms and the susceptible germplasms were differences significantly (P<0.05). After feeding on the high resistant germplasm IRCI12, E. sexmaculatus could not complete their development and reproduction, the survival rate of the adult was only6.80%, female adults could only lay4.90eggs on average, however, no eggs could hatch. In compared with the susceptible germplasms, the resistant rubber germplasms extended the developmental duration of each stage and reduced the fecundity, egg hatchability,offspring female percentage and offspring survival rate were significantly lower. It laid the foundation for the mite resistance mechanism studies of rubber germplasms.3. The nutrient contents in the mite resistant rubber germplasms leaves were significantly different with those of in the susceptible rubber germplasms leaves (P<0.05). The contents of sugar(S), proline, S/N in the leaves of resistant rubber germplasms was significantly more than those of in the leaves of susceptible rubber germplasms, they were1.4-3.5times,1.4-5.0times, and1.6-8.2times, respectively. On the contrary, the contents of free amino acids, nitrogen (N) and vitamin C (Vc) in susceptible rubber germplasms leaves were1.3-3.7,1.2-2.4,1.8-4.9times higher than those of in the resistant rubber germplasms leaves, respectively. These results suggest that the rubber germplasms on E. sexmaculatus resistance and rubber germplasms leaves free amino acids, nitrogen(N) and vitamin C (Vc) was a significantly negatively correlated (P<0.05, correlation coefficients were0.9553,0.9813and0.9521), while and sugars(S), proline and S/N was a significantly positively correlated (P<0.05, the correlation coefficients were0.9768,0.9671and0.9635), It suggested that the lower content of vitamin C (Vc), free amino acids and nitrogen (N) as well as the higher content of S/N, proline, and sugar(S) might lead to the fewer eggs E. sexmaculatus females laying and fewer days adults surviving in the leaves of resistant rubber germplasms.4. The contents of secondary metabolism products increased after the leaves were damaged by E. sexmaculatus, however, more significant increasing were detected in the resistant rubber germplasms than those of in the susceptible rubber germplasms (P<0.05). the resistant rubber germplasms contain higher total phenol, malondialdehyde, tannic acid more than the susceptible rubber germplasms, the former is the latter’s1.21to2.09times,1.23to1.98times,1.18to2.79times; after the leaves were damaged by E. sexmaculatus, the resistant rubber germplasms in leaves total phenol, malondialdehyde, tannic acid content increase rate was also significantly higher than the susceptible rubber germplasms. Compared with those before damaged the resistant rubber germplasms in leaves total phenol, malondialdehyde, tannic acid content, at the leaves were damaged1d and4d is greater than0.99mg/g,5.50X10-2mg/g,0.70mg/g, respectively before damage increased1.60to2.20times and1.69to2.26times,1.60-2.04times and1.69-2.15times,1.73-2.25times and1.86-2.38times, and the susceptible rubber germplasms in leaves total phenol, malondialdehyde, tannic acid content after E. sexmaculatus harm with also increased, but the increase was small, total phenol,malondialdehyde, tannic acid content at the leaves were damaged1d and4d is less than0.58mg/g,3.27X10-2mg/g,0.41mg/g, respectively before damage increased1.02to1.21times and1.09to1.28times,1.01-1.11times and1.02-1.20times,1.11-1.27times and1.15-1.23times. Correlation analysis showed that the rubber germplasms on E. sexmaculatus resistance and the rubber germplasms leaves total phenols, malondialdehyde, tannic acid content increased of E. sexmaculatus damage after was a significant positive correlation (P<0.05, the correlation coefficient R was0.9068and0.9229,0.9408and0.9526,0.9401and0.9336), It suggested that the changes of the secondary metabolism products contents are associated with the mite resistance of rubber germplasms.5. The activity of the protective enzymes POD, SOD, CAT and PPO increased after the leaves were damaged by E. sexmaculatus, however, more significant increasing were detected in the resistant rubber germplasms than those of in the susceptible rubber germplasms (P<0.05). Compared with those before damaged, the activity of POD, SOD, CAT and PPO in the resistant rubber germplasms leaves increased by1.91-2.20and1.96-2.22times,2.00-2.26and2.10-2.34times,2.06-2.35and2.12-2.40times,2.45-2.62and2.53-2.70times, respectively after they were damaged1d and4d by the mite. However, in the susceptible rubber germplasms leaves, those of them only increased by1.15-1.26and1.20-1.34times,1.16-1.24and1.20-1.30times,1.09-1.20and1.15-1.35times,1.22-1.34and1.29-1.38times, Correlation analysis showed that the rubber gennplasms on E. sexmaculatus resistance and the activity of the protective enzymes POD, SOD, CAT and PPO increased after the leaves were damaged by E. sexmaculatus was a significant positive correlation (P<0.05, correlation coefficients were0.9445and0.9435,0.9012and0.9437,0.9393and0.9323,0.9334and0.9390). It suggested that the changes in POD, SOD, CAT and PPO activities in the rubber germplasms leaves are associated with the mite resistance of rubber germplasms.The activity of the protective enzymes POD, AsA-POD, PPO, SOD, CAT, and a-NA/p-NA EST, however, in each stage of the mite fed on resistance rubber germplasms were significantly decreased compared with those of them fed on susceptible rubber germplasms (P<0.05), only0.25-0.63times of those of them fed on susceptible rubber germplasms. Correlation analysis showed that the rubber germplasms on E. sexmaculatus resistance and the E. sexmaculatus body protective enzymes POD, AsA-POD, PPO, SOD, CAT and a-NA/p-NA EST activity decreased after feeding on rubber germplasms a significant positive correlation (P0.05, correlation coefficients were0.9376,0.9278,0.9374,0.9321,0.9383,0.9396/0.9390;0.9404,0.9272,0.9458,0.9322,0.9267,0.9346/0.9318;0.9356,0.9294,0.9423,0.9345,0.9429,0.9374/0.9360;0.9223,0.9382,0.9393,0.9488,0.9420,0.9253/0.9387). It might be a good explanation for E. sexmaculatus that could not well complete their development and reproduction in the resistant rubber germplasms. |
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