| Producers often use excessive chemicals to promote the growth of fruits and vegetables and control all kinds of preharvest and postharvest diseases, which seriously endangers the food safety of human being. Bio-fertilizer, biological control agents, biocides not only can promote the growth of plants and control plant diseases and postharvest fruit diseases, but also reduce input of chemical fertilizers and pesticides. Piriformospora indica can be used as biological agents to promote plant growth, improve products quality, and confer biotic and abiotic stress tolerance to its host plants. In this study, tomato and Chinese celery were selected to study the effects of P. indica inoculation on plants growth and nutritional quality. Meanwhile, the possibility of P. indica induced resistance against Tomato Yellow Leaf Curl Virus (TYLCV) in tomato plants and green mould caused by Penicillium digitatum in citrus fruit were investigated. The effects of P. indica inoculation on suppressing main postharvest diseases of tomato were assessed. As well as the effects of preharvest P. indica colonization in tomato roots on the resistance of postharvest fruits were measured. Here physiology and biochemistry, molecular biology and Microarray Chips were employed to reveal the possible mechanisms of resistance induced by P. indica. The main findings are as follows:(1) Two weeks after P. indica inoculation, the main root length, average lateral root number and root biomass was improved in T07-4 cultivar resistant to TYLCV. While in T07-1 cultivar susceptible to TYLCV, shoot biomass and plant total biomass was enhanced significantly. The plant heights in 2nd-4th week and leaf number in 6th week for T07-1 tomato plants were increased than controls, respectively. But only in 4th week the plant height was improved in T07-4 tomato plants. P. indica improved the early yield of susceptible T07-1 tomato, but had no effect on the early yield of T07-4 and the total yield of cherry tomato. P. indica inoculation improved the quality of three tested tomato cultivars in some degree.(2) P. indica inoculation could significantly improve the fresh weight of shoot and root, increase the plant height and petiol number in substrate culture under greenhouse without using any nutrients during growth stages. It also markedly enhanced the nutritional quality. Ascorbic acid, total soluble protein content, the content of mineral element including sodium (Na), calcium (Ca), potassium (K), magnesium (Mg), iron (Fe) and Zinc (Zn) were significantly increased in celery leafstalk.(3) Preharvst P. indica colonization in tomato roots induced resistance to TYLCV in susceptible cultivar, significantly reduced TYLCV incidence and decreased disease index in natural TYLCV infection after 6 weeks. P. indicia enhanced pathogenesis-related(PR) genes up-regulated expressions, including PAL, PR1a, PR3a, PR3 and PR5 in inoculated susceptible cultivar T07-1 and PR3a in resistant cultivar T07-4 at two weeks after inoculation. It suggested that systemic acquired resistance was involved in P. indica-tomato system.(4) P. indicia could not inhibit the disease incidence of grey mould and black rot in cherry tomato. P. indicia could induce citrus fruit the resistance against the green mould caused by Penicillium digitatum. After 24 h P. indicia inoculation, disease incidence of green mould and the lesion diameter both were reduced. The ability of P. indicia produced to induce resistance was significantly enhanced, which might be associated with stimulation enzyme activities related with resistance, such as peroxide polyphenol oxidase activity.(5) Preharvest P, indica colonization in cherry tomato roots significantly decreased the disease incidence of grey mold, black rot and natural decay of fruit during postharvest. The enzyme activities associated with resistance in leaves were enhanced after 45 days of P. indica inoculation.The fruits from P. indica-inoculated tomato plants had lower speed of decreasing qulity. The enzymes activities related with resistance were induced during storage and the accumulation of lipid peroxidation products malondialdehyde was also reduced.(6) Preharvst P. indica colonization in cherry tomato roots can up-regulate genes mainly involved in carbohydrate, defense response (such as PR proteins, abiotic stress) and protein metabolism. Conversely, genes related to transcription, signal transduction, hormone (ethylene synthesis and regulation, jasmonic acid synthesis and regulation) and cell wall (XTH, expansin11, pectinesterase) were generally down-regulated.In short, P. indica interaction with tomato and celery promoted vegetative growth and improved the nutritional quality of celery. P. indica colonization in tomato root induced susceptible T07-1 tomato resistance against TYLCV. P. indica cell suspension could indirectly induce citrus fruit resistance against P. digitatum. Preharvst P. indica colonization in cherry tomato roots could induce fruits resistance against postharvest diseases.The possible mechanisms involved that P. indica activated the enzymes related with resistance and the expression of PR genes, inhibited the expression of cell wall metabolism related genes, thereby increased the resistance against postharvest pathogens. While inhibition of the synthesis and regulation of ethylene and jasmonic acid led to delaying ripening and prolonging postharvest life of fruit. These results provided a theoretical basis for biocontrol fungus inducing resistance to plant and fruit. And it can also provide a reference for the further applications of P. indica. |
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