Study And Screening On Extracts Of Six Woody Plants Including Myrica Rubra Against Plant Pathogens

Botanical pesticides, which had many merits such as low toxicity,high selectivity,good environmental compatibility, had become the hot spot in field of pesticide research. The research is to find out some substance from woody plants against plant pathogens for the development of botanical pesticides.In this paper, six plants including Myrica rubra,Sapium sebiferum,Quercus glauca,Ligustrum lucidum,Gardenia jasminoides,Broussonetia papyrifera were extracted with acetone .Based on this, Myrica rubra which had the best inhibitory efficiency was screened through testing 11kinds of phytopathogenic fungi by using mycelial growth rate method. Then its extracts and myricetin were determined for further antifungal activity In vitro and in vivo. Meanwhile, preliminary bioactivity of the two samples were investigated against Bursaphelenchus xylophilus In vitro. In addition, myricetin content in extracts of M. rubra leaves was tested by HPLC. The resulsts were as follows:(1) The extracts of M. rubra leaves had the strongest antifungal effects at the concentration of 1.0×10⁵mg . L^-1. Inhibition rates to seven fungi were 100%, to three fungi were above 99%, to Helminthospirium turcicum was 60.93%; and others displayed moderate bioactivity to certain of fungi.(2) The extracts of M. rubra leaves and myricetin both had strong toxicities against the mycelial growth of fungi. EC₅₀ of extracts from M. rubra against 6 fungi were ranged from 19847.23 to 25858.30mg . L^-1, the minimum and maximum were recorded in Sclerotinia sclerotiorum and Botrytis cinerea respectively ; EC₅₀ of myricetin to 3 fungi were ranged from 315.86 to 342.77 mg . L^-1, to the other 3 fungi were ranged from 690.40 to 2088.82 mg . L^-1.(3) The extracts of M. rubra leaves and myricetin both had weak inhibition to spores germination of B.cinerea and Pyricularia oryzae.Inhibition rates of the extracts of M. rubra to the two were 10.00% and 11.11% at the concentration of 2.0×104mg . L^-1,and with the inhibition rates of 5.00% and 9.16% for myricetin at the concentration of 400mg . L^-1.(4) The extracts of M. rubra leaves and myricetin in vivo both had certain inhibitory efficiency against B. cinerea on tomato,cucumber leaf, and Penicillium italicum on orange. The results showed that their protective effects were better than their therapeutic effects. At the concentration of 4.0×104mg . L^-1, protective effects of the extracts were 45.61%,40.00% and 33.92% on tomato,cucumber leaf and orange, and therapeutic effects were 42.25%,35.13% and 31.01%, separately . At the concentration of 1042.62mg . L^-1, protective effects of the myricetin were 20.02%,19.34%,18.55% and the therapeutic effects were 18.54%,17.90%,17.86%, respectively.(5) In nematicidal experiments, both of the extracts of M. rubra and myricetin had poor effects on B.xylophilus, with the correction mortality of 15.88% and 12.05% respectively for the extracts at the concentration of 2.0×104mg . L^-1 and the myricetin at the concentration of 200mg . L^-1.(6) The myricetin content of acetone extracts from M. rubra leaves was 1.12% by HPLC method.