| Wasabi (Eutrema wasabi Maxim/ Wasabia japonic Matsum), a cruciferae perennial herbaceous plant, is a unique native plant and a tradition condiment and vegetable crop of Japan. It is exclusive to other aromatic condiments for its distinctive taste and flavor. So it is popular in many people such as Japanese, Taiwanese, Thailander and Korean. There are plentiful labor resources and excellent climate resources for wasabi widely planting in Sichuan. But at present, some diseases, especially wasabi streak disease, threaten wasabi in Sichuan seriously. After investigation, we amazedly found that the incidence of diseases amounted to 90%, even to 100%. It not only led to the large loss every year but also held in the development of wasabi industry. So wasabi streak disease, also, called wasabi black leg, caused black spot on wasabi leaves and made the stem rot. Now it becomes a most important disease in the wasabi industry.We have studied on those diseased plants of wasabi collected in Sichuan Shifang and Sanjiang etc. Besides isolating, purification and appraisement experiment, we studied the biologic characters of the pathogens. Morphological character and pathogenicity of fungi isolated from diseased wasabi were studied and the results showed that wasabi streak disease was caused by Phoma wasabiae Yokogi. According to the result of study, the most suitable culture medium is PDA; temperature, pH value and light irradiation had an obtious effect on mycelium growth and spore development, the temperature suitable for mycelium growth was ranged from 4~31C, and the pH is 5-7.5. Myceliums can't survive at or over 54C(10min) and the spores will be killed at or over 49C(10min). The most favorable temperature and pH was 22-25 C and pH6.0~7.0, respectively. Darkness was propitious to the spore of P. wasabiae development. And its hosts are few comparatively.Genetic diversity of 25 P. wasabiae and 3 similar strains from Sichuan, China were analyzed using random amplified polymorphic DNA (RAPD) molecular markers on the basis of wasabi streak disease investigation, sample collection and single spore isolation and pure culture. The aim of this study is to assess and identify genetic diversity, population structure of P. wasabiae infecting wasabi and to provide some practical information for thestrategies of breeding disease-resistable wasabi and controlling this disease.We extracted the proper DNA from mycelium of 28 strains using an improved method and chose six 10-base oligonucleotides for random primers from 40 pieces. The amplified results showed some polymorphism among different species and even different strains of the same species. The amplified fragments were almost between 0.2~1.1kb. There were 575 amplified DNA bands for six primers to 28 strains including 103 polymorphism amplified DNA bands. The polymorphism of amplified DNA bands was 17.91% to the total. 28 strains from Sichuan grouped in two clusters and P. wasabiae and Macrophoma were grouped in different cluster very early. So RAPD molecular marker was a very sensitive and exact tool for classification and identification of plant pathogens. And RAPD is a efficacious and sensitive method to detect the polymorphism of DNA. The results of RAPD also showed that 25 P. wasabiae strains grouped in two sub-genuses. We can consider that there exist some polymorphism among different species and genetic diversities. To some extend this genetic differentiation is related to the space and time of collection. Also we can figure that RAPD is an efficacious method and the result of analysis reflected the familial relation among P. wasabiae and Macrophoma and even the different strains of same species. Generally speaking, the biologic diversities and genetic diversities are some simple. At the same time, six primers have amplified 16 specific DNA fragments of/! wasabiae. There werel79bp 272 bp 277 bp 308 bp 415 bp 462bp 500bp 521 bp, 540 bp 582 bp, 593 bp 677 bp 764 bp 875 bp 931 bp 1031 bp.Some of them may turn to be the effective molecular marker to P. wasabiae when they are...
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