| Potato early blight is more serious disease for potato. The disease had a great economic loss in region where potatoes were cultivated. Little work has been done on potato early blight in worldwide. Studies were carry out in many respects on the biological characteristics and genetic diversity of A.solani, the infection process and virulence differentiation to potato, The pathogenic mechanism of toxin of A.solani to Potato, and the resistance mechanism of potato to A. solani. These purpose of established the theoretical foundation for epidemiology, breeding for disease resistance and integrated control potato early blight. The results are as follows:1. By investigating of potato early blight in potato growing areas of Heilongjiang, disease happen were fairly heavy. sixty-eight strains of A.solani were separegated from the different host variety.2. By PDA plate cultivating, cultivate character of isolates of A.solani obtained from different potato-producing areas of Heilongjing were studied and biological characteristics of 5 isolates of A. solani were studied . The results showed that the isolates growed well on PDA,CMA and OA media. All the isolates growed in 10～35℃and growed difference in preferred temperature. the optimal temperature was 25～30℃for the grow of HS0801,KS0808,JG0801 and SH0806, while the optimal temperature was 20℃for the grow of NH0809. The pH 6～8 were favorable for mycelial growth. All the isolates were incompletion coincidence in pH and light. The conidia had the best germination effect in water. 25～30℃and pH 7～8 were favorable to conidia germination. The conidia germination of different isolates had idistinction. the biological characteristics of A.solani were identified and had obviously diversity.3. The transfer of culture method by cutting mycelium was used to study the suitable conditions for conidia production of A.solani. The results showed that mycelial growing on oatmeal agar medium was cut to transfer on corn agar medium could produce high numbers of spores. The optimal condition for produce conidia were 25℃, pH 7～8.4. To explore genetic diversity of A.solani, RAPD and ISSR technique was used to analyze the genetic diversity of A.solani isolates from different localities with 5 RAPD primers and 10 ISSR primers. the results showed that 5 RAPD primers amplified 53 fragments , of which 75.47% percent fragments were polymorphic, 10 ISSR primers amplified 93 fragments, of which 88.17% percent fragments were polymorphic. By UPGMA clustering, at the level of 0.81 similarity coefficient, tested isolates of A.solani were divided into 7 groups with RAPD mark, and tested isolates of A.solani were divided into 11 groups with ISSR mark. isolates of A.solani have obviously heredity differentiation.5. By field natural resistance trial and inoculation trial in indoor, the result showed that Kexin18, Kexin1 and Kexin13 were resistance cultivars, Kexin12 was middle resistance cultivar , and Hua525 Atlantic were middle susceptive cultivars,Zaodabai and Dongnong 303 were susceptive cultivars. The result guides reasonably to plant cultivars in field for control early blight.6. The infection process and ultrastructural of A. solani on leaves of potato was observed by using of microscope, scannning and transmission electron microscope. The results showed that the germ tubes penetrated the host epidermal cells junctions directly and formed infection hypha for susceptive cultivar by 8 h postinoculation, but that was 10 h postinoculation for resistant cultivar. All organelles had the solution in susceptible host by 24 h postinoculation. There was dissolution rate of cell inclusion in the resistant cultivar epidermal cells by 72 h postinoculation. The dissolution rate of cell inclusion in susceptive cultivar was faster than that in resistant cultivar. There was more amount of infection hypha e in susceptive cultivar than in resistant cultivar. This study identifies pathogenic infection way and exist difference in resistant and susceptive cultivar to resist invasion of A. solani.7. To study the virulence differentiation of A. solani from Heilongjiang, 68 isolates of A. solani were inoculated detached leaves from resistant variety, middle variety and susceptive variety. The results showed that the different strains had the virulence differentiation to 3 varieties, the strains could be divided into three types of strong, moderate, weak. Ratio of the different virulent strains had obviously idiversity in different varieties and region. The result explain the virulence differentiation of A. solani8. By comparing 4 kinds bioassay method of toxin from the culture filtrate of A. solani, the toxin was easy to be tested by using detached leaves stinged with needle . Condition of toxin produce was studied . The results showed that the optimal condition for the producing phytotoxin was 25℃, pH 6.0, dark and static culture 21d in modified Fries medium. After detached leaves treated with toxin from A. solani, there was the change of permeability cells. As the toxin concentration increasing and the treated time extending , the permeability of cell membrane was increasing gradually. Content of MDA increased . Activity of APX, content of chorophyl, protein, soluble sugar in treated leaves were lower than those in control leaves. toxin can induce injury of cell membrane, destroy photosynthesis, and inhibit synthesis of protein in potato leaves.9. To approach the resistance mechanism of potato to A. solani, development change of defensive enzymes activity and correlated biochemistry material content were studied after inoculation. The results showed that the activity of PAL, POD, PPO, SOD and CAT was ascended after inoculation, that the increase of enzyme activity in resistance cultivar was higher than in susceptible cultivar. protein and soluble sugar content were higher in resistant cultivar than susceptive cultivar after inoculation for 3 day. Caffeotannic acid content quickly increased in resistant cultivar, while change of caffeotannic acid content had fluctuation in susceptive cultivar. PAL, POD, PPO, SOD, CAT are direct correlation with potato resistance. these can become assist index for resistance cultivars breed. Change of protein and soluble sugar content are also correlated with resistance in the potato cultivar. |
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