Study On The Pathogenic Mechanism Of Bipolaris Sorghicola And Identification And Location Of Resistance Gene Against Taget Leaf Spot On Sorghum

Sorghum is important as food, wine, feed and industrial raw materials. Sorghum infectedby pathogens can lead to poor food quality and lower production.At the same time, pathogenscan produce mycotoxin to harm humans and animals. Target leaf spot which casued byBipolaris sorghicola is one of important foliar disease in sorghum varieties. At present, thereis no report on pathopoiesis mechanism as well as inheritance mechanism and moleculargenetics of this disease in China. This paper focuses on the pathogenesis and location ofresistance gene against target leaf spot in sorghum. There was a relatively systematic study inthe biological characteristics and population diversity of pathogen, the effect of pathogencrude toxins on seed germination and root growth as well as cell membrane permeability anddefense enzyme activity in sorghum radicle, the changes of sorghum leaf photosyntheticindexes and photosystem Ⅱa fter pathogen infection, the genetic law of resistance to thedisease and the marker and location of resistance gene and many other aspects. The studyobtained ideal results, parts of them filled in the blank about this research in China. Theresults provided scientific basis for breeding of resistant varieties and disease management.The main results were summarized as follows:1. Biological characteristics of pathogen which caused target leaf spot on sorghumThe result indicated that optimum temperature for pathogen mycelia growth was25-30℃, and that for conidiagermination was20-30℃.The optimum pH for conidiagermination was-6, leaning to acidity. The pathogen could use many kind of sugar as acarbon nutrient，eg.lactose and galactose. However, sorbose was not fit for pathogen myceliagrowth. Different light condition for mycelium growth was not obvious.2. The category and population diversity of pathogen in ChinaIn this diversity research, we isolated pathogens from infected target leaf spot diseaseleaves of different regions of China by morphological observation and rDNA-ITS sequenceanalysis.The results show that although these lesions have significant differences, the colonymorphology and spore morphology of pathogens are very similar. The rDNA-ITS sequence cluster analysis showed that the similarity of these pathogens with Bipolaris sorghicola reachto99%.All of these confirmed this disease caused by the same pathogen,although theselesions have significant differences.3. The Bipolaris sorghicola toxins can reduce the permeability of cell membraneThe seeds of L407B and Tx622B were treated by different concentrations of Bipolarissorghicola crude toxins.And the radicel growth inhibition rate as well as the electricalconductivity and malondialdehyde(MDA) content were determined to studied the effect ofcrude toxins of Bipolaris sorghicola on growth and embrance permeability of differentvarieties of sorghum radicle. The results showed that crude toxin could obviously inhibitgrowth of sorghum radicel. The electrical conductivity and MDA content were all higher inthe group which was treated by Bipolaris sorghicola crude toxins with same concentrationtwo days before than in control group. The electrical conductivity and MDA content werealso higher in the group which was treated by Bipolaris sorghicola crude toxins with differentconcentration on the same treated time. This demonstrates that Bipolaris sorghicola crudetoxins can reduce membrane permeability of sorghum radicle and there is a significantdifference among the different varieties of sorghum.4. The Bipolaris sorghicola toxins of pathogen can inhibit host protective enzyme activityThe method of chromometry and Ultraviolet-visible spectrophotometer were used todetect the effecte of Bipolaris sorghicola toxins on the activity of protective enzymes such asperoxidase, superoxide dismutase, phenylalnine ammonialyase and polyphenoloxidase insorghum radicle. The results showed that the activities of peroxidase, superoxide dismutase,phenylalnine ammonialyase and polyphenoloxidase were significantly reduced in thesorghum radicle after Bipolaris sorghicola toxins treatmemt. The results indicated that theBipolaris sorghicola toxins inhibited the activities of protective enzymes.5. The structure and function of PSII in sorghum leave will be damaged when pathogeninfectionUsing sorghum variety Tx622B as materials, the effects of the infection of Bipolarissorghicola on photosystem II (PSII) structure and function of sorghum leaves were studiedby determining the chlorophyll content, chlorophyll fluorescence transient, hydrogen peroxide(H2O2)content and malondialdehyde (MDA) content in leaves of sorghum.The resultsshowed that the infected by B. sorghicola induced increase in MDA content of sorghumLeaves along with enhanced lipid peroxidation and chlorophyll fluorescence transient inLeaves of sorghum appeared with some difference. Further JIP-test analysis showed that thepathogen infection seriously hurt the donor side of PSII, blocking the QAto QBelectrontransfer, reducing the activity of reaction center.6. The resistant gene to target spot leaf was controlled by recessive monogeneThe recombinat inbred lines population which was constructed by the descendent ofL407B (immune inbred line) and Tx622B (susceptible inbred line),as materials accompaniedby the method of quantitative heredity,was used to study the heredity of resistance to thedisease.According to the resistant analysis of the field investigation and X2examination,proved that the genetic mechanism was in accordant with Mendelian monogenesegregation law.Appearances in F1families was consistent with Tx622B. In F2families,resistant plants is one quarter of all plants.To verify the resistant character of L407B wascontrolled by recessive monogene preliminarily.7. The site of resistant gene on chromosomeScreened out of SSR markers which132"Xtxp-" and230"sm-" at the beginningdistribute on the whole sorghum chromosome.These markers showed polymorphic betweenresistant and susceptible parents and consistency between resistant parent and resistant-pool ofF2generation.By chromosome walking, one resistant gene to target spot leaf was mappedbetween Xtxp303and sm05014on the short arm of chromosome5within5.73M-8.15M.