Twenty-two Plant Extracts On The Control Of Anthracnose Pathogen In Rubber Tree

In recent years, the harm caused by chemical pesticides on our living environment has increased dramatically. Thus, pest control of diseases, insects, and weeds through plant-derived pesticides has become a current hotspot for research. The effects of crude extracts from Tithonia diversifolia A. Gray and some other plants on the inhibition and control of anthracnose pathogen, and induced activity in rubber tree were examined in this study, which could provide a basis for environmentally-harmLess biocontrol of anthracnose pathogen in rubber tree. The main findings run as follows:1. Twenty-two plants across Hainan were collected, dried and shattered, and then they were soaked in methanol to obtain extract solutions. The inhibitory effects of methanol extracts of the twenty-two plants on anthracnose pathogen in rubber tree were bioassayed using growth rate method. The results showed that for eight plants, among them T. diversifolia, Eupatorium odoratum L., Allamanda cathartica L., Murraya exotica L., Eupatorium catarium Veldkamp, Datura stramonium L., Bidens pilosa L., and Euphorbia hirta L., methanol extracts at a concentration of0.1g/mL had inhibitory effects on the activity of anthracnose pathogen, with the inhibitory ratio ranging from21.46%to47.07%.2. T. diversifolia, E. odoratum L., and A. cathartica L. were selected to do bioassay experiment at different concentrations (0.05,0.075,0.1,0.5,0.75g/mL), and their virulence effects were obtained. The results showed that the EC50for T. diversifolia was0.08g/mL, and EC750.1g/mL, respectively, with R2being0.7163; the EC50for E. odoratum was0.11g/mL, and EC750.26g/mL, respectively, with R2being0.9905; the EC50for A. cathartica was0.17g/mL, and EC750.38g/mL, respectively, with R2being0.9505.3. Inhibitory effects of crude extracts of T. diversifolia and E. odoratum on the anthracnose pathogen were measured using pot experiments, and certain effects were determined. Extracts from T. diversifolia at the concentrations of EC50and EC75significantly inhibited the pathogen by14.89%and35.11%, respectively. Extracts from E. odoratum at the concentrations of EC50and EC75significantly inhibited the pathogen by11.70%and29.79%, respectively. Measuring the plant photochemical efficiency and quantum yield showed that extracts of T. diversifolia and E. odoratum at the EC50concentration significantly differed from the control, and extracts of T. diversifolia and E. odoratum at the EC75concentration extremely differed from the control.4. Extracts from the twenty-two plants and BTH on the induced resistance against the pathogen were measured using pot experiments. The results showed that extracts from A. cathartica, Hibiscus rosa-sinensis L. and BTH significantly induced resistance (areas of illness spot) against the pathogen in rubber tree, with the inhibitory ratio being24.39%,20.73%, and26.83%. The plant photochemical efficiency and quantum yield did not differ from the control.5. Four treatments (spraying and inoculation, spraying without inoculation, inoculation without spraying, and control) were designed to test the effects of extracts from A. cathartica on enzyme activity in rubber tree using pot experiments, and changes in activity of four enzymes in eight days suggested that when rubber trees were inoculated with pathogen, extracts at a0.1g/mL significantly elevated the activities of SOD, CAT, PAL, and POD. This indicated that the mechanism underlying this induced resistance had to do with defense enzymes.6. Five solvents were used to extract methanol solution of T. diversifolia, and the inhibitory effects of these five extracts on pathogen activity were tested in laboratory experiment. The results showed that extraction at a concentration of0.25mg/mL significantly inhibited the anthracnose pathogen, with the inhibitory ration for chloroform, petrol aether, water, butyl alcohol, and acetic ether being50.42%,25.42%,29.58%,15.69%, and34.31%, respectively.7. The virulence of extraction of methanol solution of T. diversifolia using chloroform as the solvent at different concentrations (0.05,0.1,0.15,0.2,0.3g/mL) was bioassayed. The results showed that the EC50, EC75, EC95, and R2for the extraction on the anthracnose pathogen were0.24g/mL,0.51g/mL,1.51g/mL, and0.9724, respectively.8. The physical and chemical properties of extraction of methanol solution of T. diversifolia using chloroform as the solvent were bioassayed using laboratory experiment. The preliminary results showed that the extraction could maintain a certain inhibition ration below temperature40℃, and could be stored stably. The inhibitory effect was stronger when pH was8.0. The extraction was sensitive to light, and was unstable under illumination. The time for store was quite long.These results suggest that T. diversifolia has a great application potential to control the anthracnose pathogen in rubber tree, and thus further exploitation and use of this species could be done.