Studies On The Bioactivities Of Plant Extracts And Their Synergistic Actions

In this study, the hioactivities of twenty-eight ethanol or acetone extracts of corresponding organa and parts of twenty species of plants against 3 species of vegetable pests and 8 species of pathogen fungi, and the co-toxicities of the plant extracts mixed with them and Lc mixed with Bt and abamectin were studied by different methods, the results indicated that:Among the extracts, the antifeeding rate of 10 plant extracts were more than 90% and 2 plant extracts had significant growth inhibition (>80%) to Plutella xylostella, and Laphygma exigua and Xanthium sibiricum had strong contact poison effects on the hatching larvae of P.xyloslella and their corrected mortalities were both 100%; The antifeeding rate of 1 plant extracts (Canavalia ensiformis) was more than 90% and 2 plant extracts had significant growth inhibition (>80%) to Laphygma exigua, and Celastrus orbiculatus (stem) and Solatium aculeatissimum (stem) had strong contact poison effects on the hatching larvae of L.exigua; The antifeeding rate of 2 plant extracts were more than 90% and Melia toosendan had significant growth inhibition (92.14%) to Helicoverpa armigera, and the all extracts had no good contact poison effects on the hatching larvae of H.armigera.The results, through comparatively analyzing the inhibition activity of the same plant extract to 8 species of fungi, indicated that only the inhibition effects of Sophara flavescens, X.sibiricum, Macleaya cordata (leaf), Camptotheca acuminata, and Veralrum nigritm on one or some species of fungi.were potent (above 70%), and S.flavescens was the best.The results of combinatorial (v/v) test of the plant extracts showed that 5 combinations had summationof antifeed against L.exigua and 9 combinations presented synergistic action of contact poison against 1st instar larvae, and the co-toxicity exponent of the combination of Strychnox mix-vomica and Nicotiana tabacum (2:1 ) was maximal (1401.50) . Most combinations had antogonism of poison against 1st instar larvae of L.exigua. All combinations including C. ensiformis brought about striking antifeeding activities against P.xylostella. The combinations of M. toosendan and C.ensiformis, M.loosendan and N. tabacum and the other combinations including C.ensiformis presented high contact poison action and great poisonaction against the hatching larvae of P.xylostella respectively. Most combinations had antogonism of antifeed with regard to H.armigera. The synergistic action of contact action of the combination of M.cordata (leaf) and S.aculeatissimum (stem) (1:1) was the most prominent to 1st instar larvae, and the co-toxicity exponent was up to 700.28. Combinations else hardly had poison action with the exception of M.cordata and S.aculeatissimum against 1st instar larvae of H.armigera and the most presented antogonism.The substance-Lc was extracted from the seeds of C.ensiformis refer to Rosenthal's method and the extraction rate was 2.4%. The value of Rf of Lc and standard sample (L-canavanine) was tested to be the same by the analysis of paper chromatography, which proved that Lc included L-canavanine. The results of synergistic action test showed that Lc had summation and synergistic action on Bt and abamectin in varying degrees. The co-toxicity coefficient (CTC) of the mixtures of Bt and Lc (1:5) , abamectin and Lc (1:5) were maximal, and their values were 166.47 and 191.33 respectively. The experiment of pot of the mixture of abamectin and Lc (1:5 ) proved that Lc really had synergetic action on abamectin.