Study And Screening On Inhibitive Chinese Herbal Extracts Against Cucumber Angular Leaf Spot

Thirty species of Chinese herb ethanol extracts were tested for the antibacterial activities against Pseudomonas syringae pv.lachrymans with agar-well diffusion method. The results showed that Galla chinensis,Syzygium aromaticum and Sanguisorba officinalis had strong inhibitory activity to P.syringae pv.lachrymans.The diameter of inhibitory zone of G.chinensis extract(GCE,4000 mg/L)was 15.8 mm,and it was not significant different from that of chemical bactericide(72%streptomycin,100 mg/L).The 50%effect concentration(EC₅₀)of the above three extracts was 13.46 mg/L,19.75 mg/L and 36.80 mg/L respectively.These three extracts were further tested on detached leaves for both protective and curative effect,the results indicated that G.chinensis had the best protective effect,and the control efficacy reached to 60%;the protective effect of S.aromaticum and S.officinalis were not significant.None of the three extracts had curative effect.According to above results,GCE was selected and used for the further studies.The minimum bactericidal concentration(MBC)of GCE against different strains of P. syringae pv.lachrymans was tested,and the results were the follows:MBC of GCE against PSL-F2 and PSL-F3 was 1.0 mg/mL,that of GCE against PSL-8,PSL-F5 and PSL-F6 was 2.0 mg/mL,and that of GCE against PSL-2,PSL-F1 and PSL-F4 was more than 4.0 mg/mL.The result showed that different strains had different sensitivity to GCE.The inhibitory effect of GCE was measured after being treated at different temperatures and pH values.The result indicated that the inhibition activity of GCE increased after being treated with 121℃and was stable after being treated with -20℃～100℃.The inhibition activity of GCE was stable in pH value between 2 to 8,but it decreased obviously when pH value was between 10 and 14.This experiment studied the growth curve and respiratory metabolism of P.syringae pv.lachrymans affected by GCE.The result of the growth curve experiment showed that the growth of P.syringae pv.lachrymans was inhibited by GCE at logarithmic phase.The result of respiratory inhibition experiment reveals that GCE imposed distinct inhibition on metabolic approach of EMP,TCA,HMP by measuring the inhibition rate of GCE and three representative inhibitors,and the approach of TCA was the most important inhibition way.