Biological Control Of Soilborn Phythopathogens Including Ralstonia Solanacearum, Phytophthora Capsici, And Meloidogyne Incognita On Pepper And Tomato

Ralstonia solanacearum (Smith) Yabuuchi et al., Phytophthora capsici Leonian, and Meloidogyne incognita (Kofoid&White) Chitwood with hundreds of hosts, strong tolerance and ineradicable habits are all important plant soil-borne pathogens in crops. No appropriate disease-resistant cultivar and chemical pesticide with low toxicity and high efficacy were used commonly. Vegetables field per year in Huai’an was about87,000hectare. Half of them were protective fields such as plastic houses. Continuous growing vegetables resulted in more and more seriously happened soil-borne diseases including Ralstonia wilt, Phytophthora blight, and Meloidogyne root-knot, and the mixed happen diseases. A good choice is to use biopesticides to control these soil-borne diseases. The living bacterial antagonists can cause several beneficial effects to crops, including resistance to pathogens, promotion of plant growth, and improvement of crop production quality, being harvested in advance and prolongation of harvesting period. Moreover, they are safe for crops and environment, and can promote sustainable development of agriculture.Antagonistic bacterium Bacillus subtilis Cohn strain AR12was used to control Ralstonia solanacearum on tomato in the greenhouse with90.18%biocontrol efficiency. Since phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO), peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) are associated with lignin biosynthesis and/or plant defence system against active oxygen, superoxide anion, hydrogen peroxide generation rates, and changes in PAL, PPO, POD, SOD, APX and CAT activities were studied in tomato plants. Antagonist AR12advanced and increased significantly activities of PAL, PPO, POD, SOD and APX, while CAT was degraded until80h after pathogen inoculation. As Controls, the activities of five enzymes increased less and later in tomato only treated with R. solanacearum TM15(Control2), and kept lowest level with few change in tomato with sterilised water (Control1). The maximum activities of these five enzymes in tomato treated with AR12occurred in different stages:activity of PAL, PPO, POD, SOD and APX respectively reached to the top level at48,48,12,12and12h after the pathogen was inoculated. H2O2is associated with hypersensitive reaction (HR) during systemic acquired resistance. H2O2content was increased significantly in tomato treated with AR12, but HR response was not observed. This work support the view that increased antioxidant enzyme activities could be involved, at least partly, in the beneficial effects of plant growth-promoting rhizobacteria strains on the performance of vegetable grown under the pathogen infection conditions.BCA pool was constructed before with1246bacterial antaganists whose antagonism and ability of producing active extracellular agents were identified in our laboratory. Complex diseases including Ralstonia wilt, Phytophthora blight, and Meloidogyne root-knot usually happened in Huai’an. Thirty-six bacterial antagonists from BCA pool and their forty compatible combinations were chosen to evaluate their biocontrol efficacy to the complex diseases on bell pepper under greenhouse conditions. Each combination contained two to five strains. Here we used the mixture of half of natural soil with these three pathogens from field and half "Ready Mix". Three-strain combinations resulted in obviously better average biocontrol efficiency and shoot freshweight increase than all of other combinations and single strains as well, especially BBS(Bacillus sp. AR156+Bacillus sp. SM21+Serratia sp. XY21) mixture which achieved87.18%biocontrol efficiency, and78.50%shoot freshweight increase. Then we studied BBS family including3single strain,3two-strain combination and1three-strain combination in detail by inoculating3kinds of pathogens separately. BBS mixture achieved the best biocontrol efficiency towards the above individual diseases and the best plant growth promotion. While the three single strains in BBS family had miserable performance to some single disease, for example, SM21and XY21only had the biocontrol efficiencies towards Meloidogyne root-knot of27.68%and18.33%, whereas BBS had70.43%. Each of single strains in BBS family only increased the biomass with4.85%,13.58%, and17.14%, while the BBS mixture had the biomass increase with64.67%much more than their summation. It was concluded three single strains in BBS family had different contribution to the final performance of BBS mixture, and each single antagonist in a good combination should have its own special characteristics-it’s not necessary that all have strong antagonistic activities towards every simplex pathogen-and there must be some compensations and interactions among different antagonists and plant roots.The biocontrol efficiency and yield increase were significantly different using different fertilizers mixing with the same microbial preparation (BBS mixture). In this study, four kinds of fertilizer including chicken manure with rice bran (CM), waste culture material of Pleurotus ostreatus (WCP), waste culture material of Volvariella volvacea (WCV), and ordinary inorganic fertilizer (IOF) were used to compost with BBS mixture respectively, and applied into soil before pepper seedlings were transplanted. All of these four treatments had some influences on pepper growth, fruit conserving time, and most important, on biocontrol efficiency. Compared with the blank control, treatments of three kinds of organic fertilizer mixed separately with BBS mixture achieved biocontrol efficiencies of51.48～75.65%towards mixed diseases including Ralstonia wilt, Phytophthora blight, and root-knot nematode, and yield increase of158.25～214.39%in105days after treatment, while the IOF with BBS mixture reached only biocontrol efficiencies of27.28%and yield increase of122.53%at the same time. The best treatment was that of’BBS mixture+WCP’ which obtained the biocontrol efficiencies of79.44%,80.58%and75.65%respectively30,60, and105days after transplanting, and the highest yield increase.According to the detecting result of soil nutrition, we found that BBS mixture had an obvious contribution to organic compound increase in soil. The organic compound, total nitrogen, inorganic phosphate, and inorganic Potassium contents of the soil from the treatment with’BBS mixture+WCP’were higher than those from all other treatments in the period of fruit growing stage and harvesting time. This treatment had a significantly positive function for continuable usage of field soil. Pepper fruits from three groups of organic manure with BBS mixture had obviously higher protein and vitamin C contents. These results showed that this treatment significantly improved the quality and flavor of pepper fruits. Compared with blank control, pepper rotten percent in treatment of’BBS mixture+WCP’was only50%of that of blank control. It shows the commercial value could be obviously improved.In this study we validated that BBS mixture had a good biocontrol efficiency against mixed soil-borne disease. We made a conclusion that better biocontrol efficiency, higher yield increase and more nutrition could be obtained by BBS mixture with organic fertilizer than with inorganic one. In addition, we found P. ostreatus waste culture material was the best carrier of BCA for the soil of Huai’an. These experiments showed that’BBS mixture+WCP’treatment could efficiently control multi soil-borne diseases and significantly improve soil nutrition and pepper quality.