| Maize is one of the most important crops in China which are mainly produced in the Huanghuai and Haihe Plain. The main disease on maize is corn sheath blight which can be caused by Rhizoctonia spp. Maize germplasm were identified and evaluated for resistance to sheath blight while systematic studies were also carried out on Rhizoctonia spp. .The main results gained are summarized as follows:1. One hundred and seventy-six isolates were obtained from corn sheath blight samples in Huanghuai and Haihe Plain (including Shandong, Henan, Hebei Provinces and Northern regions of Jiangsu Province) of China. Anastomosis group identification showed that the isolates belonged to multinucleate Rhizoctonia AG1-IA, AG1-IB, AG4-HG-I, AG-5 and WAG-Z and binucleate Rhizoctonia AG-A and AG-Ba. Of these, AG-1-IA was the major anastomosis group(AG)(64.20% of total isolates), followed by AG-Ba (12.50%). AG-Ba was isolated for the first time from maize in China.2. The results of biologic characteristics showed that there were discrepancies in different AGs in the optional temperature. The optional temperature of the anastomosis group of AG1-IA,WAG-Z,AG-5 were 30℃and the optional temperature of the anastomosis group of AG-A,AG-Ba,AG1-IB,AG4-HG-I were 25℃. The optimum pH value of different AGs was 5-7. The isolates under subacidity condition can grow well.3. The pathogenicity of 7 AGs were determined on one corn variety by soil inoculation. AG1-IA was the dominant virulence group, the next was AG-Ba. The pathogenicity of 129 isolates screened from AG1-IA and AG-Ba group were determined on three corn varieties by inoculation test. The results showed that there were discrepancies in pathogenicity among isolates in the same anastomosis groups.4. Phylogenetic analysis among isolates belonging to different AGs was studied based upon nuclear ITS,β-tubulin and mitochondrial SSU rDNA sequences. The results obtained from nuclear and mitochondrial sequence analyses were similar. The sequence alignment of 5.8S rDNA-ITS revealed that the isolates of the same AGs (or sub-AG) had a high sequence similarity (97-100%) and different AGs had only 64-91% sequence similarity. The result of sequence alignment of mt SSU showed that the isolates belonging to the same AG (or sub-AG) showed 99-100% sequence similarity, whereas, the isolates of different AGs also had a relatively high sequence similarity (81-99%), so the variation of mt SSU between different isolates were relatively small. So using 5.8S rDNA-ITS and mt SSU analysis can easy identified the AGs of unknown isolate. However, the results of sequence alignment ofβ-tubulin were different from frontal conclusions. The isolates of the same AGs (or sub-AGs) had a low sequence similarity. Theβ-tubulin may have relation with genetic diversity among different isolates belonging to the same AGs.5. Rhizoctonia solani AG1-IA (YWK-198) were used to identify and evaluate for resistance to sheath blight of 452 maize germplasm. 59 maize germplasm were identified in the greenhouse. The results indicated that no immune or highly resistant was found. The percent of moderate resistant germplasm were 20.34%. Most of the tested germplasm were susceptible. The percent of susceptible and highly susceptible germplasm were 30.51% and 49.15%. 393 maize germplasm were identified in the filed. The result based on the 30 days after inoculation showed that the percent of highly resistant corn inbred line were 1.27% and the percent of moderate resistant corn inbred line were 6.87%. The percent of moderate susceptible, susceptible and highly susceptible corn inbred line were 22.14%, 46.82% and 22.9%. The results based on the 60 days after inoculation showed that the percent of highly resistant and moderate resistant corn inbred line were 14.25% and 23.16%. It was higher than the 30 days'result. The percent of moderate susceptible, susceptible and highly susceptible corn inbred line were 19.34%, 22.90% and 20.39%. So the evaluate for resistance to sheath blight should contained the result of maize seedlings and adult-plant resistance.
|
PDF Full Text Request