| Cassava (Manihot esculenta Crantz) is not only the main food for 1/7 people worldwide but also the important raw material for animal feed, starch and alcoholic fermentation in China. The highly processed products of cassava are involved with food,medical, biological engineering and many other fields. Tetranychus cinnabarinus, an cosmopolitan pest mite, is one of the most important cassava pests in China. Breeding and utilizing mite-resistant cassava varieties is recognized the safest, the most economic and the most effective management strategy to control mite. The physical and chemical mechanism of cassava resistance to T.cinnabarinus was studied on the basis of resistant and susceptible cassava germplasms and the mite-resistant evaluation criteria of cassava germplasms in the field. Which provides theoretical and technical support for the study of mite-resistant mechanism, selective and transgenic breeding of cassava. The main results are as follows:1. The mite damage index and resistant grade of SC 101, SC 124, SC7 and SC 13 were calculated and identified by the method of evaluation of cassava germplasms resistance to T.cinnabarinus in the field. The mite damage index of four germplasms are 89.2, 65.8, 38.3 and 0.8. The resistant grade of four germplasms are HS, S, MR and HR.2. The physical resistance of cassava to T.cinnabarinus was studied. The results indicated that the mite-resistance of cassava germplasms was significantly positively correlated with the leaf thickness of cassava, and significantly negatively correlated with the stomatal density of leaf abaxial epidermis. There was no correlation between the mite-resistance and the leaf waxiness content of cassava. The leaf thickness and stomatal density of mite-resistant cassava germplasms were 49.51?55.39×10-4 g/cm2 and 328.02?567.59 No./mm2 , respectively. The leaf thickness and stomatal density of mite-susceptible cassava germplasms were 45.35?50.79×10-4g/cm2 and 492.22?571.56 No./mm2, respectively. Therefore, the leaf thickness and stomatal density of cassava could be used as indicators of evaluating the cassava germplasms resistance to T.cinnabarinus.3. The nutrients content in cassava germplasms leaves was determined and analyzed.The correlation between the mite-resistance of cassava germplasms and the content of water,soluble sugar,soluble nitrogen,free amino acids and reductive-form ascorbic acid in cassava leaves had not found. Therefore, the content of water and other nutrients of cassava leaves couldn't be useful indicators for evaluating the cassava germplasms resistance to T.cinnabarinus.4. Correlation analysis revealed that the malondialdehyde (MDA) content and the increase of MDA and flavonoid after cassava invaded by T.cinnabarinus were significantly negatively related to the mite-resistance of cassava germplasms. There was no correlation between the content or the changes in content of total phenol and tannic acid and the cassava mite-resistance before and after cassava damaged by T.cinnabarinus. The content of MDA in the leaves of mite-susceptible cassava germplasms was obviously more than those of in the leaves of mite-resistant cassava germplasms before cassava damaged by T.cinnabarinus. There was no significant difference in flavonoid content of mite-resistant and mite-susceptible cassava leaves before the mite damage. After the cassava leaves were damaged by T.cinnabarinus, the ratio of MDA and flavonoid content in the mite-susceptible cassava leaves before and after damaging were 1.04-1.16 times and 1.03-1.17 times, respectively, while in the mite-resistant cassava leaves, the ratio of MDA and flavonoid content were 0.79-0.97 times and 0.96-0.98 times, respectively, which is distinctly lower than those of in the mite-susceptible cassava leaves. The content and the changes in content of total phenol and tannic acid were significantly different in cassava germplasms leaves, but had no correlation with the mite-resistance of cassava germplasms. |
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