| Broomcorn millet(Panicum miliaceum L.) is one of the most important grain and cash crops in arid and semi-arid areas, with the characteristics of short growth period, drought resistance, barren tolerance and rich nutrition. Head smut is the most serious disease in broomcorn millet, causing great reduction of yield and quality. Therefore, it is significantly important to analyse the genetic diversity and virulence variation of pathogen, identify the resistancegrade of broomcorn millet accessions, study the physiology mechanism of head smut resistance, screen effective fungicide, and determine proper cultivation measures for resistance breeding and disease control.Since broomcorn millet is a kind of regional crop, there have been few researches about broomborn millet and head smut. In this study, we analysed the genetic diversity of pathogen collected from different areas of China using RAPD and SSR; identified the resistance grade of broomcorn millet germplasms and varieties; screened a set of differential hosts and analyzed the virulence variation of pathogen; compared the change and difference of the activities of antioxidase and disease-resistant related enzymes, contents of protein and sugar, as well as the isozyme bands before and after infection at different growth stages; screened effective fungicide by lab toxicity test and field efficiency trials; studied the effect of sowing dates on head smut incidence and broomcorn millet yield. The main conclusions are as follows:(1) The symptoms on ear of infected plants included 4 different types: black powder bag, rosette, hedgehog and black powder grain. The teliospore of head smut pathogen was brown sphericity under optical microscope and could be seen tiny protuberance on the wall under electronic scanning microscope. The morphological characteristics and ITS sequence alignment indicated that the pathogenic fungus tested in this study was Sporisorium destruens. The optimal temperature and pH for teliospore germination was 25 ℃ and 5, respectively. Formaldehyde could promote teliospore germination. Among the tested carbon and nitrogen resources, glucose and KNO3 were the best. The temperature of 25 ℃ and the pH of 7 were suitable for growth and sporulation. The most suitbable media for the fungus growth were Czapek and PDA.(2) S. destruens isolates collected from Heilongjiang, Jilin, Liaoning, Inner Mongolia, Hebei, Shaanxi, Shanxi and Gansu provinces had a moderate genetic diversity and a relative consistent genetic background. Among 100 RAPD primers used, 28 primers showed polymorphism. A total of 381 fragments were amplified, of which 373 were polymorphic with a polymorphic rate of 97.90%. For the SSR markers, 40 of 111 primer pairs showed polymorphism and provided a total of 119 bands, of which 109 were polymorphic accounting for 91.60% of total bands. A higher polymorphism of RAPD loci was found than that of SSR loci. The clustering patterns generated by RAPD and SSR markers were different from one another. The genotyping data obtained using RAPD and SSR markers were combined and used for constructing the dendrogram, which showed that the 51 isolates were divided into three lineages at similarity of 0.7425. There was no significant correlation between genotypes and geographic origins of the isolates.(3) The results of 3-year identification for head smut resistance showed that 261 germplasms presented a significant resistance variation and resistant germplasms occupied a great proportion, among which 12MD-2 and 12MD-250 were immune to S. destruens in all 3 years. Among 66 varieties, only blest jachee and orlovski karlik, which were both from Russia, showed high resistance; while, the varieties provided from China did not show stable resistance. Three germplasms possess the desirable characteristics of high resistance, dwarf, early maturity and high yield, and could be applied in production. Sixteen S. destruens isolates had a certain degree of virulence variation and were separated into three pathotypes based on the reaction on these differential hosts.(4) After infected by S. destruens, the activity of SOD increased, and the increasing amplitude and SOD activity of resistant varieties were larger than that of susceptible ones at three-leaf stage. POD activity increased in resistant varieties continuously but decreased in susceptible ones at later stage. MDA content of resistant varieties was lower than that of susceptible ones. After inoculated by S. destruens, APX and GR activity had negative correlations with resistance. Compared with control, AsA content of resistant varieties increased rapidly and kept a high level, while the AsA content of susceptible varieties increased slowly and decreased at later stage. The GSH content increased at three-leaf and jointing stages and decreased at heading and filling stages. After induction, the ascending ranges of PAL activity of resistant varieties were significantly higher than that of susceptible ones at three-leaf, jointing and filling stages. At three-leaf and jointing stages, chitinase of resistant varieties was significantly higher than that of susceptible ones. The β-1, 3-glucanase activity had a positive correlation with host resistance at heading stage.After inoculation, the soluble protein content had no correlation with head smut incidence; the total soluble sugar content had negative correlation with resistance at three-leaf and filling stages; the reducing sugar content had negative correlation with resistance at three-leaf and jointing stages. S. destruens infection could cause the change of POD, EST, SOD and PPO isozymes of different disease-resistant varieties, and the band increments of resistant varieties were greater than that of susceptible ones.In conclusion, the activity of SOD, POD, APX, GR, PAL, chitinase and β-1, 3-glucanase, and the content of MDA, AsA, GSH, total soluble sugar and reducing sugar, as well as POD, EST and SOD isozyme, could be used as the assistant indices for resistance identification.(5) Lab toxicity test and 2-year field efficiency trials of six fungicides, tebuconazole, thiophanate-methyl, diniconazole, carbendazim, difenoconazole and thiram were conducted for screening an effective fungicide to control head smut. The results showed that tebuconazole exhibited the greatest inhibition to S. destruens, while thiram showed the weakest toxicity. Diniconazole inhibited seed germination most strongly. Tebuconazole had the best control efficacy, followed by diniconazole, thiophanate-methyl and carbendazim, while thiram had the worst control efficacy. Carbendazim could impact the area of the second leaf and the third leaf, dry weight of leave and the number of tillers, significantly. Compared with control, all of the fungicide treatments caused the reduction of grain weight per plant in varying degrees, but increased the grain yield. The yields of broomcorn millet under the treatment of tebuconazole were the highest in both years. Therefore, among all the six fungicides, tebuconazole had the best control efficacy with the lowest concentration, and could be used in practical production.(6) The responses of different broomcorn millet varieties to sowing date were varied. Except 05 was not infected on all 5 sowing dates, the rest exhibited the highest incidence on sowing date Ⅰ, with no significant difference among all the other sowing dates. Resistant varieties Bameng Xiaoheimi and 05 gained the highest yield on sowing date Ⅲ, hence June 15 th could be chosen as the optimum sowing date for them; susceptible varieties Zashu and Huang yingmi obtained the highest yield on sowing date Ⅱ, so June 1st was recommended as the most suitable sowing date for them. Incidence had a significantly negative correlation with soil temperature on 5 cm, and low temperature contributed to head smut occurrence. Incidence had no correlation with soil water content on 20 cm. |
PDF Full Text Request