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

Piriformospora indica is an endophytic fungus which colonizes in many plants' roots. It promotes plant growth by increased uptake of nutrients like N and P, enhances stress tolerance and confers induced systemic resistance against various biotic agents.Chinese cabbage (Brassica chinensis L.) belongs to Cruciferae Brassica and is closely related to Brassica campestris L. and Arabidopsis thaliana L. Heynh. It can be easily grown and has short growth period. Chinese cabbage is one of the most important vegetable cultivated in the middle and lower reaches of Changjiang River. The crop is seriously affected by various biotic and abiotic stresses. The thesis is mainly about disease resistance, growth promotion and stress tolerance in Chinese cabbage conferred by Piriformospora indica and the preliminary study of their mechanisms. The salient findings of the research are:1 Established the co-cultivation system to study the growth promotion in Chinese cabbage. Through comparing 1 plug to 2 plugs treatments, we found the treatment with 2 plugs showed more growth promotion through increased main root length, number of lateral roots and biomass. The fungus colonized in the roots and the pear-shaped chlamydospores were observed under the microscope.2 P. indica conferred resistance to Alternaria brassicae (Berk) Sacc. The root biopriming with P. indica protected the foliar infection of the pathogenic fungus. The spores of Alternaria were inoculated on Chinese cabbage leaves which have already co-cultivated with P. indica for 2 days. After inoculating the spores, we checked the disease resistance protein (DRP) gene on the 1st and 3rd day. After the 1st day inoculating the pathogen, the gene expression in leaves increases and is higher in P. indica-colonized plants than non-colonized plants. But the expression in roots is almost the same on the 1st day. On the 3rd day, the expression both in leaves and roots increase sharply. The results of percentage disease index after inoculating the pathogen spores showed that on the 6th day, all uncolonised plants were severely infected by Alternaria brassica, compared to the colonized plants. On the 10th day, all roots and leaves of the uncolonised plants were dead. Compared to control, there are only some small disease spots on leaves of colonized plants.3 P. indica promoted the biomass of Chinese cabbage. After co-cultivation for 6 and 10 days, we measured the main root length, average lateral root length, root and shoot fresh weight. It showed that P. indica treatment increases main root length 105.00% and 88.99% on each day; twice the number of lateral roots; average lateral root length increases 80.77% and 70.33%; root fresh weight enhances 84.93% and 73.09% and shoot fresh weight increases 73.64% and 107.86% compared to control. P. indica promotes the main root length, no. and length of lateral roots and bushy hariy roots.4 IAA alone doesn't play any role in the growth promotion. The treatment of roots with IAA, P. indica, cell wall extract and water diffusible extracts showed that P. indica treatment did the best growth promotion and IAA alone doesn't show any growth promotion. Both cell wall and water diffusible extracts promoted the growth but lower than P. indica treatment. In addition, we did the semi-quantity RT-PCR and found that the expression of auxin gene has no difference in P. indica and mock treatments.5 In drought stress, P.indica confers the plants resistance through enhanced antioxidant activities and the expression of drought-related genes and proteins. We imitated the drought stress by dealing with PEG The results showed that the antioxidant enzymes activities (POD, SOD, CAT) with P. indica treatment increases faster and higher than control. In addition, the MDA content is lower than control. The fungus retards the drought-induced decline in the photosynthetic efficiency and the degradation of chlorophylls and thylakoid proteins. The expression of the drought-related genes DREB2A, CBL1, ANAC072 and RD29A was upregulated in the drought-stressed leaves of colonized plants. Furthermore, the CAS mRNA level for the thylakoid membrane associated Ca2+-sensing regulator and the amount of the CAS protein increased.