Analysing Of Resistance Genes To Rice Blast In Rong 18B

Rice blast,caused by Magnaporthe grisea,is one of devastating rice diseases.The practice shows that breeding and utilization of resistant varieties are the most economical,effective and environmentally friendly methods to control the rice blast.The resistant rice varieties usually will lost resistance when wildly promoted in 3⁵ years because of genetic variation of rice blast fungus,and breeding resistant varieties is a long-term task to prevent and control of rice blast.Rong18B is the maintainer line of Rong18A,bred by Crop Research Institute,Chengdu Academy of Agriculture and Forestry Sciences,and is an elite sterile line with high resistance to rice blast and strong combining ability of.So far,twenty-three new hybrid rice varieties that one of their parents is rong18A have been approved new varieties both level provincial or national.Rong18A is the sterile line of high resistance to rice blast.Howere,it is not clear that which genes are responsible for the resistance to rice blast in rong18A.The purpose of this study is to explore the genes of resistance to rice blast in rong18B by gene mapping,analysis expression of genes and sequencing,and to make better use of blast resistant genes and reasonable layout of varieties.The main results are as follows:1.F₂ population was constructed by cross-fertilizing rong18B and Lijiangxintuanheigu of high susceptible to rice blast.M14Ga089 strain that can obtain resistant individual plants and susceptible individual plants with 3:1 was screened by inoculating and identifying 7strains in F₂ population.Bulked extremes and recessive class were used to map gene.It was found that a gene between GDAP51?10,376,027bp?and RM19918?12,320,121bp?of chromosome 6 is resistance to M14Ga089,and it was named Pir18.2.Only those genes of Piz locus have NBS-LRR structure in this interval by searching genome of Nipponbare,so to analyze genes of Piz locus in rong18B.Linkage markers were used to analyze correlation blast resistant genes previously cloned at Piz locus in rong18B.It was found that the band was different in corresponding linkage markers among rong18B,GM4?Pigm?,IR10?Pi2?,IR11?Piz-t?and IR22?Pi9?,which demonstrates that difference is existed between Pigm,Pi2,Piz-t and Pi9 in rong18B and Pigm,Pi2,Piz-t and Pi9 previously cloned.Using sequencing and alignment,it shows that Pi9 in rong18B has basic group deletion that causes the appearance of termination codon in advance in comparison to Pi9 previously cloned.This suggests that Pi9 in rong18B doesn't contribute to blast resistance of rong18B;Piz-R18B is the allele of Pi2,Pigm and Piz-t in R18B;Piz-R18B is difference of 55 basic groups in comparison to Pi2,14 basic groups in comparison to Pigm,54 basic groups and 3 basic group deletions in comparison to Piz-t,and Piz-R18B doesn't cause appearance of termination codon to appear,that can form a complete protein.Therefore,Pir18 may be a new blast resistant gene in this interval because blast resistant genes previously cloned that Pi50/Pigm,Pi2,Piz-t and Pi9 are different in comparison to Pi50/Pigm,Pi2,Piz-t and Pi9 in rong18B and Piz-R18B has high expression in rong18B by expression analysis.Difference of resistant spectrum was found between IR10?Pi2?,GM4?Pigm?and rong18B by spraying inoculation,and rong18B has a wider and more promising resistance spectrum.These results show that Piz-R18B may be the gene that confers resistant to rong18B for rice blast.That is to say,Piz-R18B could be Pir18.3.We analyze expression quantity of blast resistant genes previously cloned in rong18B.It was found that Pi25,Pi9,Pib,Pid2 and Pik-loc have some expression.Then,those genes which have some expression were sequenced.It was found that Pid2 of rong18B has a mutation of two bases and doesn't have mutation of amino acid in comparison to Pid2 of YiXiang 1B.Pi25 of rong18B doesn't have mutation of basic group in comparison to Pi25of GM2.Howere,Pia,Pikp,Pita and Pib of rong18B have mutations or insertions of basic groIVups,so Pia,Pikp,Pita and Pib can't confer resistant to rong18B for rice blast.In conclusion,Pir18 confers resistant to rong18B for M14Ga089 strain,a new blast resistant gene in 10,376,027bp to12,320,121bp interval,and may be anew allele of Piz locus.Pid2 and Pi25 may confer resistant to rong18B for rice blast.