| Tetranychus cinnabarinus (Boisduval) is a kind of worldwide harmful mites, which occurred seriously year by year in China, has become one of the most important pest attacking maize. Using chemical pesticides is the main method to control T. cinnabarinus. However, the use of miticide has led to "3R" problem. Cultivating and growing the resistant variety to mite is one of the most economic and effective approaches of integrated management of mite. Currently, some studies on maize resistance to mite focus on screening resistant material. Biochemical mechanism of maize risitanceto mite has not been very clear yet.In this thesis, the resistance level of 8 maize inbred lines were evaluated, the relationship between resistance to T. cinnabarinus and the activities of protective enzymes, the systematic induced effects of mite infestation, as well as induction effect of Zea mays defense signal molecules to mite infestation were studied, aiming to investigate the inducible resistance mechanism of maize to T. cinnabarinus, providing the theoretical basis for integrated management of T. cinnabarinus. The results are as follows.1.Identification of 8 maize inbred lines resistance to T. cinnabarinusWith maize covered with net in field and potted in the laboratory, and then inoculated with mites, the resistance of 8 maize inbred lines at seedling and heahing stages to Tetranychus cinnabarinus were evaluated on leaf hazard index.The results showed that the resistant level of 8 maize varieties at the seedling stage were consistent with that at the heahing stages. Leaf hazard index of H1014168 is the smallest with 0.31 at seedling stage and 0.34 at heahing stage, belonged to the high resistant inbred line,while that of H1019005 is the highest with 0.81 at seedling stage and 0.73 at heahing stage,belonged to the high susceptible inbred line.2. Relationship between the activities of protective enzymes in leaves of 8 maize inbred lines and resistance to miteTo clarify the relationship between the activities of protective enzymes and the different of mite resistant ability,8 maize inbred lines were examined 2-8 days after inoculating with T. cinnabarinus in seedling and heahing stages, and the changes of their protective enzymes (POD, SOD, PPO, PAL, CAT, CI and TI) were measured. The results indicated that, at the seedling stage, the activities of PPO, POD, SOD, TI, CI in leaves of 8 maize inbred lines were upward trend follow up days after inoculating. In addition, the activities of PAL and CAT were downward trend and the decrease rate was slower at 2 and 6 days after infesting of T. cinnabarinus. The activities of PPO, POD, SOD, TI and CI in leaves of 3 resistant maize inbred lines were significantly higher than 5 susceptible maize inbred lines. The analysis of linear correlation showed that after feeding the mites, there were considerably negative correlation between the average of increase rate of the PPO and CAT activities (x) and leaf hazard index (y), and the correlative coefficients were r=-0.75063(y 2.0415x+1.8454); r=-0.7483(y=-1.2045x+1.0674) respectively. Besides, there were significantly negative correlation between the average of increase rate of POD. SOD, TI and CI activities (x) and leaf hazard index (y); the correlative coefficients were r=-0.8467 (y=-0.5395x+0.703); r=-0.8374 (y=-0.8331x+0.8349); r= 0.9695 (y=-0.8589x+0.7615) and r=-0.9720(y=-1.1568x+0.8863) respectively. At the heahing stage, the activities of POD, SOD and TI in leaves of 8 maize inbred lines were an increasing trend follow up days after inoculating. The activities of CI reached the maximum in the second day. The activities of POD, SOD, TI and CI in leaves of 3 resistant maize inbred lines were significantly higher than susceptible maize inbred lines, meanwhile, the activities of PPO and PAL were different changes by level. The analysis of linear correlation showed that after feeding the mites, there was a significant negative correlation between the average increase rate of the PPO and PAL activities (x) and leaf hazard index (y), and the correlative coefficients were r=-0.7137 (y=-1.553x+1.1552); r=-0.7878 (y=-4.0668x+3.5226) respectively. Moreover, the negative correlation (P<0.01) between the average increase rate of POD, TI and CI activities (x) and leaf hazard index (y) was remarkable, the correlative coefficients were r=-0.9083 (y=-2.3447x+1.8392); r=-0.8560 (y= 3.5544x+2.9294) and r=-0.9046 (y=-5.04x+4.067) respectively. The above results showed that the overall trend of the protective enzyme activities was related to the damage inducement of harmful mites. Five protective enzymes play an important role in cultivating of resistant and sustainable maize inbred lines controlling mite.3. Induction of Zea mays defense signal molecules in response to T.cinnabarinus infestationHow infestation of Tetranychus cinnabarinus induces the generation of six defense signal molecules, including jasmonic acid (JA), salicylic acid (SA), ethylene (ET), nitricoxide (NO), abscisic acid (ABA) and hydrogen peroxide(H2O2) in Zea mays seedling leaves were studied. We measured the contents of these signal molecules at 0,24,48,72 and 96 h after inoculation (hai) of T. cinnabarinus by spectrophotometry (SP), high-performance liquid chromatography (HPLC) or enzyme-linked immunosorbent assay (ELISA).Our data demonstrated that the contents of JA, ABA and H2O2 increased rapidly, were summited at 24 h after inoculation of 30 individuals per leaf, and reached to 4.13-,3.84- and 3.20-fold of the un-inoculated control, respectively. Subsequently, the contents of JA, ABA and H2O2 descended sharply from 24 to 48 hours. The contents of ABA and H2O2 stayed at low level from 48 to 96 hours,whereas that of JA reached another peak at 96 h. The content of NO rose up from 24 to 48 h, and were summited at 48 h after inoculation of 30 individuals per leaf, and reached to 5.09-fold of the control. The contents of SA and ET have been increasing during the whole time of infestation, were summited at 96 h after inoculation of 30 individuals per leaf, and reached to 5.17 and 2.99-fold of the control, respectively. The contents of six signal molecules in leaves infested by 30 individuals were significantly higher than those in un-inoculated controls.These results suggest that the infestation of T. cinnabarinus can induce accumulation of JA, SA, ET, NO, ABA and H2O2 in seedling leaves of Zea mays, and they are activated sequentially during the infested process.4. Systematic induced effects of Tetranychus cinnabarinus infestation on 4 kinds of chemical defenses in Zea mays inbred linesThe systematic induced effects of Tetranychus cinnabarinus infestation on chemical defenses in Zea mays were investigated. T. cinnabarinus adult females were inoculated on the first leaf at two leaves stage of two maize inbred lines,’H1014168’(the mite infestation tolenrance)and’H1014591’(the mite infestation sensitve),and we measured the contents of DIMBOA, total phenol, trypsin inhibitors (TI) and chymotrypsin inhibitor (CI) in the second leaf and in the roots at the seventh day after inoculation.Our data demonstrated that the contents of DIMBOA,total phenol, TI and CI in the second leaf, as well as TI in the roots of’H1014168’and ’H1014591’were significantly higher than those of the un-inoculated control at the seventh day after inoculation.However, the contents of DIMBOA,total phenol and CI in the roots of the former significantly increased, whereas the contents of DIMBOA and CI in the roots of the latter were not significant, total phenol significantly decreased. These results suggest that the infestation of T. cinnabarinus can systematically induce accumulation of DIMBOA, total phenol, trypsin inhibitors (TI) and chymotrypsin inhibitor (CI), however, systematic induced effect on the higher resistant inbred line was stronger than the lower resistant inbred line to the mites. |
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