Study And Evaluation Of Hybrid Rice Resistance To Bacterial Blight And Rice Blast

Rice will continue to be the major human staple crop well into the next century. The rice bacterial blight(BB) and blast(BL) have been recognised as the most explosive and potentially damaging diseases of rice despite decades of research towards its control. The principal focus of this study was to sreen fancy three-line hybrid combinations and inbred lines with BB- and BL-resistance, serving for rice breeding and commercilizing. 202 three-line hybrid rice combinations and 7 Cytoplasmic male sterile(CMS) lines were:used as materials, and their resistance levels were surveyed by leaf-inoculation method in the rice nursery. Some useful results were obtained. 1.The BB- and BL-resistance of three-line hybrid rice Only 15 of 202 combinations tested, which accounted for 7.44%, were resistant, or moderately resistant(MR), to the representing strain of the pathotype IV ZJ173, others were susceptible, moderately susceptible(MS) or highly susceptible(HS) to this race. Of these 202 rice hybrids tested, 6 combinations were resistant, highly resistant(HR) or moderately resistant(MR), to BL, which only accounted for 2.98%. The rest were BL-susceptible(MS-HS). Therefor most of three-line hybrids can resist neither BB nor BL. most Combinations bred in Hubei province and south china area wouldbe needed to imoprove in the aspect of BB- and BL-resistance.2. The BB- and BL-resistance of the leading hybrids In this research, 11 three-line hybrid combinations with large acerage in Hubei were surveyed. But none of them was resistant to BB strain ZJ173 and BL. The potential disease risk would be under the way towards hybrid rice yield in Hubei province.3.The BB- and BL-resistance of CMS lines7 CMS lines utilized frequently were tested in this study. All of them weresusceptible to BB strain ZJ173 and BL. Perhaps this would be the basic reason why most three-line hybrid rice combinations are not good at resistance to these diseases.4. The relationship of the resistance between combinations and their CMS linesThe analysis on inheritance of BB- and BL-resistance in several CMS lines ' and their relevant showed that the resistance to BB of most combinations could be improved well when CMS lines with/some dominant gene or several mino卤 resistant-genes were crossed .The resistance level of exhibited the parents differently with the same dominant gene Xa-4 in different; hereditary backgrounds. Most combinations, made by CMS lines with dominant or minor resistant gene(s) distinted in resistance, especially in the combinations crossed by such long-used lines as Zhenshan 97A and II-32A. The resistancelevel of the CMS lines with genetic origin of wild rice or landraces was different, and that of their combinations was higher.When the susceptible CMS lines were crossed by the restorer lines with several minor BL resistant-genes, most of their combinations were not BB- or BL-resistance. This implied that the resistance of three-line hybrids were tightly related to CMS line. Most of the combinations were resistant when susceptible CMS lines were cossed with the restorer lines with major gene resistance. The contribution of restorer lines to hybrids in blast resistance is also very important.The approaches to the resistant hybrid rice improvement are discussed in the paper.Extending the utilization of resistance genes and exploiting new resistance resources, combining traditional breeding methods with modern molecular biotechnology, enriching the genetic background of CMS line restorer and maintainer lines can improve the resistance of parents so as to breed resistant combinations.