Preliminary Study On The Toxin Produced By The Pathogen Of Hylocereus Undatus Rot

Plant pathogenic fungi herbicide are the use of pathogen and metabolites as active substances to control weeds.They are easy to be cultivated and controlled,economic and efficient.It will not cause the"3R"problem and pollution in ecological environment,which attracted more and more attention to all countries in the world.Colletotrichum gloeosporioides BWH-1 and Neoscytlidium dimidiatum BWH-3 are pathogenic strains isolated from stems of Hylocereus undatus rot.In this paper,Colletotrichum gloeosporioides BWH-1 was used as the research material.The extraction of metabolites of the pathogen,the pathogenesis to Hylocereus undatus and Aloe Vera,the pathogenicity to 18 kinds of weeds and the stability of the toxin were preliminarily studied.The toxic producing conditions of strain BWH-1 were optimized,in order to prove the possibility of its metabolites as biological herbicides.By acupuncturing culture filtrate of the strain BWH-1 and BWH-3 into the stem of Hylocereus undatus,it was found that the strain BWH-1 liquid culture had certain effect on Hylocereus undatus,and the strain BWH-3 culture could not cause the decaying of Hylocereus undatus.The fermentation filtrate of strain BWH-1 was extracted or deproteinized by different organic solvents.The bioassay showed that the ethyl acetate extract（crude toxin）of the strain BWH-1 fermentation filtrate had the highest pathogenic activity,and the symptoms were the same as those of the origin toxin.The Electron microscopy observation showed that the strain BWH-1 toxin filtrate had a destructive effect on the stem bark,spongy tissue,and vascular bundle tissue of the Hylocereus undatus,and the cell was severely damaged.Aloe vera leaf tissue test showed that it also had a certain damage effect on the leaf tissue of the Aloe Vera,which was similar to the stem injury of Hylocereus undatus.The stability test of strain BWH-1 toxin filtrate showed that the filtrate of strain BWH-1 had good stability to the outside environment,stable at the temperature of 30⁸0℃,and the activity was lost at 90¹00℃for 60 min.The activity was stable at pH 3⁹.5,and greatly weakened under the condition of strong alkaline.Tolerance to ultraviolet radiation.Using seed germination inhibition method,Celosia argentea,Ageratum conyzoides,Eleusine indica,Bidens pilosa,Digitaria sanguinalis,Mikania micrantha,Amaranthus retroflexu and Echinochloa crusgalli 8 kinds of hybrid seeds were treated with different concentrations of toxin,the results showed that all concentrations of toxin had inhibitory effect on weed seed germination,the higher the crude toxin concentration,the better the inhibition effect.When the crude toxin was 0.4 mg/mL,the germination inhibition rates of the eight weed seeds were 60.8%,71.96%,49.94%,80.12%,42.02%,49.28%,75.62%,and52.97%.Using the method of rhizome growth inhibition,10 kinds of weeds were treated with different concentrations of toxin,including,Bidens pilosa,Echinochloa crusgalli,Abutilon theophrasti,Eleusine indica,Ageratum conyzoides,Amaranthus retroflexus,Chenopodium serotinum,Celosia argentea,Plantago asiatica and Mikania micrantha.The results showed that the toxin could inhibit the growth of the rhizomes of the tested weeds.When the crude toxin was 0.4 mg/mL,the inhibition rates for the roots of tested weeds were 81.07%,66.74%,52.01%,58.78%,75.79%,75.12%,53.22%,62.07%,75.02%,54.91%,and the inhibition rate for the stems were 75.17%,61.46%,47.5%,51.93%,63.69%,71.19%,46.18%,65.5%,72.51%,47.5%,respectively.And when the toxin at high concentration,the weeds of the weeds will become dark and rot.Anredera cordifolia,Mikania micrantha,Armgrass,Typhonium giganteum,Alternanthera Philoxeroides,Wedelia chinensis,Bryophyllum pinnatum and Eichhornia crassipes were tested for their biological activity at different concentrations by needle point method.The test results showed that when the crude toxin concentration was higher than 0.1 mg/ml,the pathogenicity was strong,and the rot spot was obvious.The pathogenicity of Eichhornia crassipes and Bryophyllum pinnatum was especially obvious,and the diameter of the lesion was more than 5.8 mm.The pathogenicity is weak when the concentration of crude toxin is less than 0.05 mg/ml.0.1 mg/ml crude toxin was used to needle the leaves of the 8 weeds.The disease spots were measured to determine the pathogenicity of the weeds at different processing times.The results showed that the weeds were treated for 7 days,the lesion size was 6.8 mm,5.5 mm,4.8 mm,6.2 mm,6.3mm,5.7 mm,7.7 mm,and 7.4 mm,respectively.A single factor optimization test of carbon source,nitrogen source and pH were carried out on the liquid fermentation condition of strain BWH-1.The optimized medium were as follows:sucrose as carbon source was,NaNO₃ as nitrogen source,pH was 6.5.Adding juice from the stem of Hylocereus undatus showed that adding 5%could increase the bioactivity of toxin filtrate of BWH-1 strain.On the basis of single factor test,the culture time,inoculation quantity,temperature and pH of orthogonal experiment were selected to optimize the toxic production conditions.The best fermentation conditions of strain BWH-1 were as follows:culture time 8d,temperature28℃,pH 6.5,inoculation amount 4/100 ml.Under the best culture conditions,the inhibitory rate of the toxin filtrate to the root of Bidens pilosa was 53.46%,which was 9.85%higher than that before the optimization.