Sdudy On Identification Technology And Resistance Mechanism Of Stem Canker And Black Scurf In Potato By Rhizotonia Solani

The stem canker and black scurf in potato by Rhizotonia solani is one of the main diseases in Inner Mongolia. The studies on identification technology and resistance mechanism were important in theory and practice. The resistance and identification technology on28different potato varieties to R. solani were studied. The resistance mechanism were research from potato structure and physiological and biochemical. The results were as follows:1. The pathogen of stem canker and black scurf by R. solani on potato was isolated from underground stems. The isolation had pathogenicity to potato. It’s identification result showed that it was R. solani AG2-1.2. The toxin of R. solani AG2-1had pathogenicity to potao seedling. It was a key pathogenic factor. But the low concentrations toxin can promote seedlings growth of potato.3. The resistance identification technology system was established to stem canker and black scurf in potato. The ways of potato pieces inoculated with R. solani and seedlings treated with toxin can identify preliminaryly. Then the tests of inoculating with wheat bran inoculum2～4g per potato seed were conducted in field.4. The resistance of the28potato cultivars was significantly different to R. solani AG2-1but none of these was completely resistant. Most of them were susceptible. The cultivar Diseree showed the less percentage of infection by R. solani, while the cultivars Atlantic, Favorita, Shepody showed a high percentage of infection on tubers.The potato varieties of long growing period and the deeper epidermis color were resistant than the ones of short growth period and white skin.5. In the infection process of pathogen, the initial infection time were4h,8h and8～12h at tubers, underground stems and stems. The infection structure were a few loose infection cushion, most were appressorium, there were lobate, spherical, trident form, foot and irregular shape, infection pegs were formed from the appressorium. There were more infection structure at stems than the underground stems and tubers.The infection site were mainly cuticle cracks, lenticels, cell gap, wound and a small amount of mycelium direct invasion at tubers. At underground stem the infection site were mainly crack, lenticels, epidermal cell gap and a small amount of hyphae direct invasion. At stems the invasion site were mainly the intercellular and direct invasion breakthrough epidermal, a small amount of mycelium from the stoma invading.6. Susceptible cultivars Atlantic had more infection structures, larger and more lenticels, thin cuticle, rough epidermis, less wax than the resistant varieties Diseree.7. The physiological and biochemical resistance mechanism showed that the toxin of R. solani AG2-1can increase the POD, PPO and SOD activity in potato seedlings, and the several enzyme activitys of resistance varietie were all higher than the susceptible one, at24-96h, The CAT, PAL, chitinase, β-1,3-glucanase activity were increased also, but the changes and resistance were not related. The content of proline and Lignin were all increased after inoculating and the resistance cultivar was greater than the susceptible one. The MDA content and cell membrane permeability were all increased also. O～96h, MDA content of susceptible cultivar was greater than the resistance one. The cell membrane permeability of susceptible varieties increased earlier and more.8. The relations on nutrition of potato and resistance showed that the soluble starch content and resistance was positive correlation, on the other hand, the soluble protein content was negatively correlation with the resistance, soluble sugar and amino acid had no obvious correlation with the resistance.