Study On The Control Agents Of Xanthomonas Axonopodis Pv. Citriy

The citrus bacterial canker disease occur in most citrus-growing areas of our country, and is very serious to the citrus industry. So the thesis studied on the control agents of Xanthomonas axonopodis pv. citri, including chemical bactericides and botanical fungicides.The antibacterial activity of 193 species of plants belonging to 90 families and collected from the north and southeast of Guangxi province was studied. Based on the activity screening, the active ingredients of Ampelopsis cantoniensis (Hook. et Arn.) Planch. and Pithecellobium clypearia (Jack) Benth. showing high inhibitory activity against X. axonopodis pv. citri were isolated and the chemical structures were identified. The antibacterial mechanism of these Chinese herbal medicine plants was also preliminarily studied. The antibacterial activity of 14 bactericides was determined. Based on the screening of bactericides, the inhibitory activity of binary mixtures between antibacterial plants and bactericides against X. axonopodis pv. citri was Preliminary studied.The antibacterial activity of 193 plant extracts against X. axonopodis pv. citri was determined by plate culture medium coating method. The results showed that 15 plant extracts had high antibacterial activity, and could be completely inhibited the growth of X. axonopodis pv. citri in 72h at 10mg/mL. These plants included A. cantoniensis (Hook. et Arn.) Planch., P. clypearia (Jack) Benth., Pterocarya stenoptera C. DC., Gelsemium elegans (Gardn. et Champ.) Benth., Stephania dielsiana Y. C. Wu, Stephania kwangsiensis Lo, Polygonum perfoliatum Linn. Tetrastigma planicaule (Hook.) Gagnep., Eucalyptus robusta Smith, Psidium guajava Linn., Eucalyptus tereticornis Smith, Ternstroemia gymnanthera (Wight et Arn.) Beddome, Pterolobium punctatum Hemsl., Clerodendrum cyrtophyllum Turcz. and Lumnitzera racemosa Willd.. Tow plant extracts Cibotium barometz (Linn.) J. Sm. and Rubus corchorifolius L. f. could be completely inhibited the growth of Xanthomonas axonopodis pv. citri in 48h at 10mg/mL. And there were 23 plant extracts could be completely inhibited the growth of pathogenic bacteria in 24h at 10mg/mL, including Gnetum montanum Markgr., Paliurus ramosissimus (Lour.) Poir., Reynoutria japonica Houtt., Elaeocarpus hainanensis Oliver, Impatiens siculifer Hook. f., Actinidia chinensis Planch., Stephania cepharantha Hayata, Cocculus orbiculatus (Linn.) DC., Toxicodendron Succedaneum (L.) O. Kuntze, Rhus chinensis Mill., Osbeckia opipara C. Y. Wu et C. Chen, Callistemon viminalis (Soland.) Cheel., Euscaphis japonica (Thunb.) Dippel, Gordonia acuminata Chang, Eurya nitida Korthals, Schima superba Gardn. et Champ., Eurya patentipila Chun, Camellia oleifera Abel., Garcinia oblongifolia Champ. ex Benth., Alchornea trewioides (Benth.) Muell. Arg., Phyllanthus urinaria Linn., Excoecaria agallocha Linn. and Acorus tatarinowii Schott..The minimum inhibitory concentration (MIC) of 15 plant extracts that had high antibacterial activity to X. axonopodis pv. citri was further determined. The results showed that the extract of A. cantoniensis (Hook. et Arn.) Planch. and P. clypearia (Jack) Benth. had the best inhibitory effect to X. axonopodis pv. citri, with the MIC of 2mg/mL both, and the second were P. stenoptera C. DC. and G. elegans (Gardn. et Champ.) Benth., both with the MIC of 6mg/mL, and the third were S. dielsiana Y. C. Wu and S. kwangsiensis Lo, both with the MIC of 8mg/mL. The MICs of the other 9 plant extracts were 10mg/mL.The antibacterial activity of the extracts from different parts of A. cantoniensis (Hook. et Arn.) Planch. and P. clypearia (Jack) Benth. were determined. The results showed that the active parts of tow plants were branches and leaves, and the leaves was the mainly part. The MICs of the extracts from the branches and leaves of A. cantoniensis (Hook. et Arn.) Planch. were 4mg/mL and 2mg/mL, respectively, and the MICs of the extracts from the branches, leaves and flowers of P. clypearia (Jack) Benth. were 4mg/mL, 2mg/mL and 4mg/mL, respectively.The extract of the branches and leaves of A. cantoniensis (Hook. et Arn.) Planch. were preliminarily separated into 4 parts by the method of liquid-liquid extraction, and the result of bioassay show that the active ingredients mainly consist in the ethyl acetate fraction. The active fraction 2-11 was gained from the ethyl acetate fraction by silica gel column chromatography. The extract of the branches and leaves of P. clypearia (Jack) Benth. were preliminarily separated into 4 parts by the same way, and bioactivity measurement showed that the active ingredients mainly consisted in the ethyl acetate fraction. One active compound was isolated from the ethyl acetate fraction of P. clypearia (Jack) Benth. by several silica gel column chromatography and thin-layer chromatography using activity-directed isolation method, and identified for methyl gallate by NMR and MS. The MIC of methyl gallate was 1mg/mL.To screen the effective bactericides, the MICs of 14 bactericides against X. axonopodis pv. citri was determined in laboratory using plate culture medium coating method. Among the 14 bactericides, the MICs of 10 bactericides including 60%thiophanate-methyl·iprodione WP, 80%mancozeb WP, 72%streptomycin SP, 2%kasumin SL, crystals of copper sulphate, 53.8%kocide WDG, 25%metalaxyl WP, 64%oxadixyl·mancozeb WP, 20%bismerthlazol WP and 58%metalaxyl·mancozeb WP were 10mg/mL, 10mg/mL, 2.5mg/mL, 2.5mg/mL, 0.625mg/mL, 0.3125mg/mL, 0.3125mg/mL, 0.1563mg/mL, 0.1563mg/mL and 0.0391mg/mL, respectively. The inhibitory activity of these 10 bactericides from high to low was 58%metalaxyl·mancozeb WP, 20%bismerthlazol WP and 64%oxadixyl·mancozeb WP, 25%metalaxyl WP and 53.8%kocide WDG, crystals of copper sulphate, 2%kasumin SL and 72%streptomycin SP, 80%mancozeb WP and 60%thiophanate-methyl·iprodione WP. For the other 4 bactericides 50%dexon WP, 20%zinc thiazole SC, 15%triadimefon WP and 3%zhongshengmycin WP, the MICs were 10mg/mL(50 times dilution), 10mg/mL(20 times dilution), 2.5mg/mL(60 times dilution) and 0.3125mg/mL(96 times dilution), all above the largest test concentration. The bactericide screening showed that 58%metalaxyl·mancozeb WP exhibited highest inhibitory activity against X. axonopodis pv. citri, followed by 20%bismerthlazol WP, 64%oxadixyl·mancozeb WP, 25%metalaxyl WP and 53.8%kocide WDG.Based on the screening of bactericides, the optimum allocation of binary mixtures between antibacterial plants and 4 bactericides was seeking. The best combinations were that A. cantoniensis (Hook. et Arn.) Planch. and 53.8%kocide WDG in 1:1, A. cantoniensis (Hook. et Arn.) Planch. and 64%oxadixyl·mancozeb WP in 1:1, P. clypearia (Jack) Benth. and 53.8%kocide WDG in 1:1 and P. clypearia (Jack) Benth. and 64%oxadixyl·mancozeb WP in 1:1.The inhibited effects of A. cantoniensis (Hook. et Arn.) Planch., P. clypearia (Jack) Benth. and methyl gallate against the colony growth and the amount of the growth were determined by live bacteria counting method and dry weight method. The results showed that A. cantoniensis (Hook. et Arn.) Planch., P. clypearia (Jack) Benth. and methyl gallate exhibited high inhibitory effect, with the IC50 value of 0.1887mg/mL, 0.1802mg/mL and 0.1272mg/mL, respectively.A. cantoniensis (Hook. et Arn.) Planch. and P. clypearia (Jack) Benth. mainly influenced the logarithmic phase of pathogens. Through by inhibitting cell division to inhibit the growth of pathogens.