Study On Marine Microorganism And Its Antifungal Substances To Control Plant Disease

The 644 strains of marine bacteria were isolated from sea mud and water collectedfrom Lian Yungang sea area, and 11 strains with antifungal activity were screened by thefirst and second screening, purifying and fix quantify screening. The antifungal spectrumsof 11 strains against 8 plant pathogenic fungi were tested and the results showed that thestrains Ns-sw-6, Ps-sw-20 and Ps-sw-21 were wide antifungal spectrum and had strongantifungal activity against 8 plant pathogenic fungi, including Alternaria brassicae,Pyricularia grisea, Botrytis cinerea, Rhizoctonia solani, Sclerotinia sclerotiorum,Colletotrichum capsici, Fusarium moniliform and Phytopthora capsici. The strainsMG-sm-3, PY-sw-9 and PY-sw-1 also had high antifungal activity against 7 plantpathogenic fungi except P. capsici. Among 11 antifungal marine bacteria, only the strainPs-sw-20 can produce chitinase.In order to know whether the marine-derived antagonistic bacteria could be applied tobiocontrol or not, it was tested to control Rice Sheath Blight in pots and field. The resultsdemonstrated that the marine bacterium PY-sw-1 was a good biocontrol agent in controllingRice Sheath Blight in pots and field. The control efficacy of PY-sw-1 were 63.8 % and 61.1%, increased by 13.73 % and 25.46 % over those of Bs-916 which was an effectivebiocontrol agent from the soil after investigating in the pots for 7 and 15 days.Simultaneously, its extracellular substances' were 61.2% and 55.5 %, and increased by25.41% and 24.16 % compared with Bs-916's. In the field test, the control efficacy of thestrain were 53.9% and 50.8%, and increased by 22.96% and 41.16% compared withBs-916's. Its extracellular substances' were 53.9 % and 50.8 %, and increased by 28.64 %and 35.83 % respectively. The results in the pots and field indicated that marine-derivedantagonistic bacteria had control efficacy against plant disease and potential usefulness inbiocontrol.The fermentational broth of PY-sw-1 precipitated by Solid Ammonium Sulphate werehighly active against 7 plant pathogenic fungi, involved A. brassicae, P. grisea, B. cinerea, R.solani, S. sclerotiorum, C.capsici and E.moniliforme, but not against P.capsici. Althoughthe extracellular protein concentration of Ps-sw-20 and Ps-sw-21 were higher than others'testing by Coomassie Brilliant Blue G250, they were not against 8 plant pathogenic fungi.Conversely, the extracellular protein concentration of PY-sw-1 was approximately half ofPs-sw-20's, but had strong inhibited effect against 7 plant pathogenic fungi. The others'were weak or lost their activity against plant pathogenic fungi. The morphological toxicityof the crude antifungal proteins from PY-sw-1 to plant pathogenic fungi was revealed thatthe growth of mycelia was inhibited and atrophic, mycelia apex tumescence, distortion,tumescence and rupture.The optimum salinity and pH value of the growth of PY-sw-1 were about 3% and 7respectively, the range of optimum temperature was 25～35℃and the yield of theantifungal substances was maximal at 28℃. The antifungal activity of crude substanceswas decreased by 64.49% after treated with Protease K for 30min at 37℃, and kept partialactivity after treated with Papain, Pepsin and Trypsin. These results showed that thecomponents of the antifungal substance produced by PY-sw-1 might contain proteins. Theantifungal activity was highest when pH value was 7.0, however, and almostly lost fullantifungal activity when pH value was 2.0 or 12.0. The antifungal activity was decreased by71.97% by treatment with high temperature and pressure for 20 min. These results indicatedthat the antifungal activity of the crude antifungal proteins from the marine bacteriumPY-sw-1 was stable and broad-spectrum antifungal activity and might play an importantrole in biocontrol plant disease.By 16S ribosomal DNA gene sequence analysis, the antifungal strain PY-sw-1 wasindentified as a Bacillus ap., which is close to B.subtilis with 99.9% sequence similarity.The other marine bacterium, Ps-sw-20, which could produce chitinase, was indentified as aPseudoalteromonas sp.. It is close to P.flavipulchra with 99.6% sequence similarity. Theseresults made a foundation for studying marine bacteria and their antifungal substances oncontrolling plant disease further.