Cytological Examination On Interactions Between Mlo Near-Isogenic Lines Of Barley And Alternaria Tenuissima Causing Leaf Blight

The recessive loss-of-function mutations of barley Mlo gene mediate durable, highly effective,and broad-spectrum resistance to all known races of Blumeria graminis f.sp.hordei.Although barley Mlo mutation behaved highly effective resistence to Blumeria graminis,it is also found that the mutant plants,however, became hypersusceptible to the rice blast pathogen Magnaporthe grisea and the cereal hemi-biotrophic pathogen Bipolaris sorokiniana.The mechanism on Mlo gene in the interaction between the barley and biotrophic or saprophytic pathogen is remained unclear.In order to further verification and research the function and mechanism of Mlo gene in the resistance,cytological comparison on interactions between Mlo near-isogenic lines of barley and Alternaria tenuissima(Fr.)Wiltsh,the barley leave blight pathogen,was studied here,based on the biological assey of Alternaria tenuissima.The main results were as follows:1.The study of biological characteristics of Alternaria tenuissima showed that the optimum temperature for its mycelium growth and sporulation is 28℃.The fungus is suitable in the medium with pH 5.0 to 6.0.Continuous darkness is conducive to its sporogenesis and mycelial growth.At the same time rich nutrition in the media is not the requirement for Alternaria tenuissima growth.The fungus can effectively use a variety of carbon and nitrogen to grow.This suggests that the fungus has a stronger survivability in artificial media.2.The Mlo loss-of-function mutants could enhance resistance to the leave blight pathogen with both papilla-associated resistance and hypersensitive response(HR). The effective papilla,which could arrest the pathogen to invade into barley epidermal ceils,was 15%in the wild Mlo barley,Ingrid(Mlo);and,in contrast,49%,51%,55% in mlo-3,mlo-4,and mlo-5 mutants,respectively.3.The HR of the invaded barley epidermal cells might limit the fungal further extension into adjacent mesophyll cells.The HR percentage in epidermal cells was 64-69%in mlo mutant lines but only 26%in the wild Ingrid.These indicate that Mlo gene regul ate the defense responses by different way to various pathogens.4.Be sides by invading from stomata to inside tissue,it was found that the fungus could also penetrate the barley epidermal cells directly.And though most of the hyphae indeed spread between the mesophyll cells,someone could also invade and grow within barley mesophytl cells,even in the living ones.