Growth Promotion, Disease Resistance And Stress Tolerance In Tobacco Conferred By Piriformospora Indica And The Preliminary Study Of Mechanisms

Piriformospora indica belongs to Piriformospora, Sebacinaceae, Sebacinales, Agaricomycetes, Basidiomycota, fungi. It resembles in many aspects to arbuscular mycorrhizal fungi (AMF).Similar to AMF, this fungus promotes plant growth, increases resistance of colonized plants against fungal pathogens and tolerance to abiotic stress. In contrast to AMF P. indica can grow axenically on different synthetic media.Tobacco(Nicotiana tobacum L.) belongs to Solanaceae Nicotiana and is one of the most important economic crops and model plants. It can be easily grown and has short growth period. China is the biggest country of tobacco products in the world. The crop already covers15million acres every year and represents1%of China’s total farmland. The crop is seriously affected by various biotic and abiotic stresses. The thesis is mainly about growth promotion, disease resistance and stress tolerance in Tobacco conferred by Piriformospora indica and the preliminary study of their mechanisms. The salient findings of the research are:1Established the co-cultivation system to study the growth promotion in Tobacco. Through inoculation1plug,2plugs,3plugs,4plugs,10plugs treatments on MS medium, we found the treatment with2plugs showed the most growth promotion through increased main root length, number of lateral roots and biomass. Through comparing MS medium with PNM medium, we found the treatment with2plugs on MS medium showed more roots and higher biomass than the treatment with2plugs on PNM medium. The fungus colonized root cortical cells in the form of mycelium or chlamydospore under the microscope. The chlamydospores were pear-shaped, round or oval.2P. indica promotes the biomass and protein of Tobacco. After co-cultivation for10and20days on medium plates, we measured the main root length, the number of lateral roots, root and shoot fresh and dry weight. It showed that P. indica treatment increased main root length9.02%and14.15%on each day;1.7fold the number of lateral roots; on the20th day of co-cultivation shoot fresh weight was2.36fold higher than control;dry weight was1.61fold; root fresh and dry weight was1.75fold. P. indica treatment increased the plants height, leaves length and width8.25%,8.93%and5.71%compared to control pot Tobacco one hundred and twenty days old. At the same time P. indica enhanced the protein content60.01%.3P. indica increases resistance to Alternaria longipes, Colletotrichum gloeosporioides, Pythium ultimum and Rhizoctonia solani. The root biopriming with P. indica protects the foliar infection of the pathogenic fungus. The Alternaria longipes and Colletotrichum gloeosporioides were inoculated on Tobacco leaves which had already co-cultivated with P. indica. We measured the lesion diameter on the4th,6th and9th day after inoculating. After6days inoculating Alternaria longipes, the disease diameter of non-colonized plants was1.67times that of P. indica-colonized. After the4days and9days inoculating Colletotrichum gloeosporioides, the disease diameter of non-colonized plants was10fold and7.24fold that of P. indica-colonized. The Pythium ultimum and Rhizoctonia solani were inoculated at the base of Tobacco which had already co-cultivated with P. indica for one month. After inoculating Pythium ultimum and Rhizoctonia solani7days and20days, the roots of control plants turned brown and the leaves were wilting, became yellow. Compared to co-cultivated plants with P. indica just grew slowly, the leaves turned yellow and the roots were healthy.4P. indica strengthens drought tolerance and salt-stress tolerance in Tobacco. In drought stress, P.indica confers the plants resistance through enhanced antioxidant activities and the expression of drought-related genes. We imitated the drought stress by dealing with PEG. The results showed that the antioxidant enzymes activities (POD, SOD, CAT) with P. indica treatment increased faster and higher than control. In addition, the MDA content was lower than control. The expression of the drought-related genes HSP70-1and SGN-U231627were up-regulated on the9th and6th hour after PEG treatment in the drought-stressed leaves of colonized plants. We analyzed P. indica’s potential to protect Tobacco from salt stress through treadmill and pot tests. When co-cultivated Tobacco plants with P. indica were exposed to low (100mM NaCl) and moderate (300mM NaCl) salt concentrations on MS plates, they could regenerate roots and regrow, but could not grow under high (500mM NaCl) salt concentrations condition. However, plants without P. indica treatment only could regenerate roots and regrow under low salt concentration, could not grow under moderate and high salt concentrations. Pot experiments were also carried out to study effects of salt stress between P. indica treatment and control plants. Results showed that plants with P. indica treatment are more salt-tolerant than control under200mM salt concentration condition.