| Crazy top caused by Sclerophthora macrospora, is a destructive maize disease, which is local economic important in many countries in the world. The first report of the disease on maize was published in Italy in 1902. Since it was first found in Shandong Province, China, in 1974, the disease expanded fastly and there were some reports from 17 provinces and 48 counties. In some maize production areas crazy top has becoming a major threat to production, such as in Ningxia and Xinjiang.Maize crazy top is a seed-borne and seed-transmitted disease. Why did the disease expand to some of provinces during a short time although there were few seeds or no seeds harvested from infected plants. Based the morphologic characteristics and cell wall composition of Sclerophthora macrospora, this research tries to make clear of the relationship between mycelia in seeds and the spread of maize crazy top using techniques of hypha special stain method and molecular marker method. Also the conditions of disease development, maize resistance and disease control measureses were studied. The main results are as follows:1. Four methods of mycelia stain were compared, including zinc-chlor-iodide, I2-H2SO4, chitin stain and cotton blue lactopheno, in Pythium inflatum, Phytophthora capsipi, Exserohilum turcicum, Bipolaris maydis and Fusarium moniliforme, which are in different taxonomic groups with celluloses or chitin in the cell wall. Results showed that using cell wall stain methods 5 fungi species can been distinguished in two group: oomycytes and true fungi. Zinc-chlor-iodide is specific to stain the mycelia of Oomycetes quickly and easily. Using the stain method of zinc-chlor-iodide the mycelia fractions in maize seeds and symptomized tissues, collected from infected plants, were detected. The pathogen mycelia fractions were found in the pericarp, endosperm and embryo of maize seeds and were not found in the plant tissues. The fact pointed that Sclerophthora macrospora can infect the seeds and is seed-borne pathogen.2. By the collection of the oospores of Sclerophthora macrospora and comparison of methods of DNA extraction, an effective procedure of DNA extraction from the oospores of Sclerophthora macrospora was made. The internal transcribed spacer (ITS) region was amplified with the general primer (ITS1 and ITS4). The DNA segment amplified was cloned and sequenced. Based on the rRNA-ITS sequence three specific primers were designed and synthesized, including SMI, SM2 and SM3. SM3 primer was specific one for amplifing DNA of Sclerophthora macrospora and no amplification of DNA of maize tissues.3. On glasshouse and in field the effects of the soil collected from crazy top field, infected plant tissues and seeds were evaluated for the disease development under different soil moisture conditions. Only few plants showed typical symptoms. The result showed that it is difficult to induce germination of oospores of Sclerophthora macrospora4. There were no good results on identification of maize resistance, and using fungicides and culture method to control the disease. For reducing the disease severe controlling soil moisture is the effective measure as well as avoiding planting the susceptible varieties. |
