| Sheath blight disease (SBD), one of the three most serious diseases in worldwide, causes severe loss in yield and quality under favorable environmental conditions. The resistance of rice to SBD is a typical quantitative trait with low heritability of resistance materials. Therefore, there is no any immune or highly resistant variety in production so far.YSBR1 developed by our research group is a new germplasm with stable and high resistance to sheath blight. In this study, the biological interactions between R. solani and YSBR1, or susceptible cultivar Lemont were investigated.The main results were as follows:1、The resistance of YSBR1 and Lemont to R. solani showed significant difference in the field stage and seedling stage and in vitro.The resistances of YSBR1 and Lemont were evaluated in both field and greenhouse. Six days after inoculation, the varieties of lesion lengths on resistant and susceptible was significant difference. The lesion lengths of YSBR1 and Lemont were 0.9357 cm and 6.6167 cm, respectively, under field condition; and were 1.2923 cm and 4.2347 cm, respectively, under greenhouse condition. At 30 d after heading in the field, YSBR1 and Lemont presented significant difference on disease scores with 3.92+0.684 of YSBR1 and 7.18+1.364 of Lemont. At 48 hours after inoculation with detached tiller, YSBR1 leaf sheaths only showed a small piece of gray spots, while Lemont displayed obvious water-soaked disease symptom. At 7 days after inoculation in seedling stage, YSBR1 and Lemont showed significant difference on disease scores with 2.86+0.857 of YSBR1 and 8.28+1.752 of Lemont.2、The infection structure and morphological differences of R. solani on YSBR1 and Lemont showed significant difference.(1) Through optical microscope observation, the amount of hyphae and infection cushion in sheath of YSBR1 were less than that in Lemont observed at 48h after inoculation. The morphological difference of mycelium in YSBR1 and Lemont also presented apparently difference.(2) Through scanning electron microscope observation, the number of infection structures between YSBR1 and Lemont at 60h and 72h after inoculation were found having significant difference. Compared with the resistant cultivar YSBR1,the Lemont had more infection cushion and appressoria, and had much more regular mycelial. YSBR1 was found having ability to inhibit mycelial growth or to dissolve hyphae. In addition, this study firstly discovered that R.solani mycelia can exist in between upper and lower surfaces of leaf sheath, which could be account for the difficult controlling of rice sheath blight prevention with fungicide.3、Effect of secretion materials of rice leaf sheath on infection cushion formation of Rhizoctonia solani was investigated.The results showed that there were sparse mycelia and no infection structure formation on the water agar surface. However, the infection cushion was observed on the surface of water agar after added leaf sheath inner washing liquid. On the contrary, the surface of water agar with leaf sheath inner chloroform washing solution could not form infection cushion.4、Metabolism profile in response to R. solani of two different varieties were investigated.(1) At 2 days after inoculation, we found although the lesion length of YSBR1 and Lemont only showed slight difference, the diseased area on YSBR1 showed significantly smaller than that on Lemotn. This indicates the changes on physiological and biochemical level between YSBR1 and Lemont had occurred at 2 days after inoculation, which was the appropriate time-point for metabolism analysis.(2) Identification of metabolites of YSBR1 and Lemont.The endogenous metabolites in four groups of samples were analyzed and identified using multiple mass spectrometry database. The results showed that 65 possible endogenous metabolites were identified in Lemont. There were 33 and 62 metabolites in the control group and the treatment group, respectively. Total of 63 possible endogenous metabolites were identified in YSBR1. There were 45 and 62 metabolites in the control group and the treatment group, respectively. All the identified metabolites were organic compounds except the hydroxylamine. There were 54 common endogenous metabolites in Lemont and YSBR1 including 19 peptides,17 organic acids,7 carbohydrates and their derivatives,4 lipids,2 phenylpropanoid and ketones,2 nucleic acid and vitamin and cofactor,1 organic heterocyclic compounds and inorganic compounds.(3) Identification of differential metabolites between YSBR1 and Lemont.Through a series of analysis, we found that total of 19 metabolites showed difference between control and treatment in the Lemont, of which there are 7 organic acid,4 carbohydrates and their derivatives,4 lipid,2 polypeptide and 2 phenylpropanoid and ketones. For YSBR1, total of 28 kinds of metabolites displayed changes between treatment and control, except for the reduction of threonine, others metabolites were all increased after inoculation, which includes 8 polypeptide,7 organic acids,6 carbohydrates and their derivatives,4 lipids, phenylpropanoid and 1 flavonoid substances and vitamins and coenzyme factor. A total of 16 common differential metabolites were identified between YSBR1 and Lemont, which were quinic acid, sorbitol, trehalose and linoleic acid content, indicating these substances involved in rice against R. solani. Total of 11 differential metabolites were specifically found in YSBR1, which included aspartic acid, valine, isoleucine, phenyl alanine, serine, lysine and tyrosine, ribose, ubiquitin (vitamin B5),3-hydroxy propionic acid, and aconitic acid. According to the bioinformatics, the differential metabolites involved in the signaling pathway producing benzene C ammonia phenolic substances and related metabolic pathways and a variety of amino acids induce rapid could be mostly associated with strong resistance of YSBR1 to sheath blight. |
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