| Sorghum head smut causes by [Sporisorium reilianum (Kuhn) Langdon & Fullerton], is one of the important diseases of sorghum and distributed all over the world. Head smut disease can directly damage the ear structure of sorghum and can cause harvests to nothing. The sorghum head smut was increased prevalence in recent years and it caused severe yield losses in sorghum production. This paper focuses on pathogenesis of sorghum head smut and on the varieties disease-resistant for gene mapping, the biological characteristics, population diversity, pathogenicity, physiological differentiation of the pathogen, activity of defense enzyme activity when the pathogen invasion on sorghum, resistant characteristics and disease inheritance of genetic markers and so on. It was provided a theoretical basis for sorghum diseases resistant breeding and disease prevention and control. The main findings were as follows:1. A clear relationship between head smut of sorghum with different symptoms and pathogenic speciesThe pathogens of sorghum head smut with 8 kinds of symptoms from sorghum production area in Liaoning, jilin and Heilongjiang province were identified based on the pathogens culture characteristics and rDNA-ITS sequence analysis. The results showed that the colony morphology and rDNA-ITS sequence of pathogens were consistent with the characteristics of S. reilianum. The pathogens of sorghum head smut with different symptoms were belonging to the species of S. reilianum, and not belong to others. The cause of the symptoms difference of sorghum head smut is still to be further studied.2. It was cleared that the physiological specialization and races distribution of S. reilianum on sorghumFor the questions on sorghum head smut was severly occured in sorghum production recent years, the pathgenicty of 44 single spore strains of S. reilianum which from the main producing areas of 10 provinces in China were tested on 12 differential hosts under the artificial soil inoculation. The results showed that:(1) There were 4 physiological races in the pathogen population of China, race 3 was a dominant race. (2) The geographic distribution of the races was clear:The race 1 was mainly in parts area of Jilin province and Guizhou province, The race 2 was mainly in Inner Mongolia autonomous region and Guizhou province of sorghum production area, The race 3 was a dominant race and widespread throughout the major sorghum production areas of Heilongjiang, Jilin, Liaoning,Shanxi and Sichuan procinves; The race 4 was mainly distributed in provinces such as Shanxi province and Shaanxi province of sorghum production area. (3)The differential hosts for races identification system was first established, the differential hosts for 4 races were Tx414 or early sumarc, Tx3197B, Tx623B or Tx622B, TAM428 and B2V4.3. Effect of pathologen of S. reilianum on the major defensive enzymes of sorghumUsing the colorimetric method by UV spectrophotometer, the changes of defense enzymes activity in plant of sorghum varieties was tested for both disease-free plant and diseased plant by artificial inoculation with the pathogen of S. reilianum. The results showed that there were differences on the activity of protective enzymes, such as PAL, POD, EST and MDA. The activity of protective enzymes had changed in diseased plant that by artificial inoculation. The enzyme activity of PAL, SOD, EST, PPO and MAD were increased, but the activity of CAT and POD were decreased. There were slight differences on activity of protective enzymes between male sterile line and maintainer line.4. The rule for evaluation of sorghum for resistance to head smut was first developed and 150 sorghum germplasm resources were evaluated by the ruleIn research on the screening of resistance resources, the rule for evaluation of sorghum for resistance to head smut DB21/T19.4-2014) was first developed. Using the artificial inoculation technique,150 sorghum germplasm resources (including male-sterile, maintainer and restorer lines) which used widely in sorghum breeding at present in China,were evaluated for resistance to sorghum head smut.47 accessions of immune resources and 6 accessions of highly resistant were identified.5. The inheritance of resistance to dominant race of sorghum head smutIn this study, the F1 and F2 population from different resistance maintainer and restorer line combinations were tested for Inheritance of resistance to dominant race of S. reilianum under artificial inoculation in the field. The results showed that sorghum resistance to head smut was completely dominant, susceptibility was recessive. There were three ways of heredity for sorghum resistance to the dominant race of S. reilianum,3:1,13:3 and 15:1. The tested varieties for resistance to race 3 of S. reilianum were mainly controlled by 1-3 pairs of nonallelic gene and an additive effect by mini-gene as well.6. Molecular marker and mapping of resistance gene against head smut on sorghumUsing bulked segregation analysis and SSR F2 population was maded by the resistant maintainer LR625 and suseptable restorer L407B for genetic analysis and disease resistance gene tags to the dominant race of S. reilianum on sorghum. The results showed that primer Xtxp 285 was found in a stable resistant line and can be used as genetic markers to head smut resistance in sorghum. The PCR amplification results showed that there was a clear and stable bands between the pool of resistant and susceptible parets, the fragment in resistant pool was about 230bp, in susceptible pool was about 250bp. Primer Xtxp285 was closely linked with resistant genes of head smut in sorghum, and therefore the gene in sorghum was located on chromosome 3, the nearest linkage marker is 7.2 cM apart from resistant gene. |
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