| Sheath blight is one of three fungal diseases in rice, caused by Rhizoctonia solani Kuhn. The disease was first discovered in Japan by Miyake (1905), later it is widely found worldwide. The disease trend more and more heaver in recent years. For a long time, preventing rice from sheath blight mainly relis on chemicals and cultivation measures, but the effect is not ideal. Therefore, we must find an effective way to solve this problem. Breeding varieties with resistance to the disease has been long considered as the most conomically and environmentally safe method to solve the disease problems.The crude toxin of Rhizoctonia solani produced in improved Richard’s medium was extracted when the cultured filtrate was absorbed by active carbon with methanol as eluant and then the methanol was evaporated by rotavapor. Use different concentrations of the toxin to do the radicle inhibit experiment by the seeds of rice varieties Lemont and YSBR1, which resistance levels to rice sheath blight are significantly different. The inhibition rates of radicle elongation then were calculated. The concentration causing the largest defference in radicle inhibition rate between the two varieties was choosed as the appropriate concentration to follow up toxins experiment.Resistant or susceptible responses of some rice varieties to Rhizoctonia solani toxins were detected and the correlation of their toxin tolerance with field resistance was calculated. The result showed that relatively susceptible varieties displayed higher sensitivity to toxins and varieties with somilar resistance level to the disease had similar levels of toxins tolerance. YSBR1shows the strongest tolerance to toxins and the highest level of resistance to sheath blight in the field. The results indicated that the detection of toxin tolerance was a good method in breeding of resistance to SB and we can use it to screen individuals with relative resistance to SB.The tolerant individuals from F2population of YSBR1/Lemont were selected by means of the method of radicle inhibition in the appropriate concentration of toxins. We selected some germinated seeds extremely susceptible and tolerant to the toxins, sowed them in greenhouse and inoculated R. solani fungus to identify their resistance to SB. The results showed that the toxin-sensitive and the toxin-insensitive individuals were respectively susceptible and resistant to the pathogen in greenhouse idetificantion with highly significant difference of resistance. In order to verify whether the difference of toxin tolerance and the correlation between toxin tolerance and SB resistance really exist, F2individuals with different toxin sensitities from above cross and another cross (YSBR1/WuLingGeng1), were screened in an experiment of field inoculating the fungus at late tillering stage. The results trended to consistent to that in greenhouse experiment, indicating that, with appropriate toxin concentration, the radicle inhibition could be used as one kind of SB resistance screening methods.Our research group has constructing chromosome single segment substitution lines (CSSSLs) using Lemont as genetic background, YSBR1as donor parents. Seeds of the CSSSLs were used to identify the toxin tolerance. There were two CSSSLs with YSBR1’ substitute segments in Chr7, which had shown both the strong toxin tolerance and SB resistance. The result suggested that a QTL of SB resistance may exist in the interval of YSBR1’Chr-7. In addition, from the F2population of YSBR1/Lemont cross, we screened toxins extremely-susceptible and-insusceptible individuals each30plants, extracted genomic DNA and equivalently mixed their DNAs to resistant and susceptible pools, respectively. In an interval of Chr6, a QTL of tolerance to the toxins was detected,. Because CSSSL of chr-6corresponding interval was not constructed, we have no any result comparing to that to above F2population. Meanwhile, linkage values of some markers in Chr7with resistance to SB, based on the result from F2population, nearly reached significant level. Therefore, the above results require further confirmation. |
PDF Full Text Request