Improving Blast Resistance Of Rice CMS Line Taonong 1A By Pi9-based Marker-assisted Selection

Rice（Oryza sativa）is one of the most important food crops in the world.However,the occurrence of rice blast seriously affects the yield and quality of rice.Breeding new resistant varieties is proved the most economical and effective measure to control this disease.To improve blast resistance of the indica cytoplasmic male sterile（CMS）line Taonong 1A and its maintainer Taonong 1B,an indica rice line 75-1-127 harbouring the broad-spectrum blast resistance gene Pi9 was employed as the donor parent,Taonong1B and Taonong1A were successively used as acceptor and recurrent parents in the Pi9-based marker-assisted selection（MAS）backcross breeding practice.The main results were as follows:1.A PCR-based co-dominant In Del marker CoInDF₁R₂ was developed according to intron sequence of the Pi9 gene.A 354 bp band was amplified from the genome of 75-1-127,while amplification product size was about 470 bp from either genome of Taonong1A or Taonong1B,and PCR products can be quickly distinguished by agarose gel electrophoresis.2.Blast resistance of Taonong1B and Taonong1A was thoroughly improved through MAS breeding of CoInDF₁R₂.Eight improved CMS lines and their corresponding maintainers were obtained in 2020,then three sets of them,Taonong 1A-Pi9-1/Taonong1B-Pi9-1,Taonong 1A-Pi9-2/Taonong 1B-Pi9-2 and Taonong 1A-Pi9-3/Taonong 1B-Pi9-3were preliminary sreened,which showing high-level blast resistance,excellent agronomic and yield traits and homozygous alleles of Pi9.3.Sterility and cross-pollination characteristics,main agronomic and yield traits of above three improved CMS lines were investigated through field cultivation assays.Finally,Taonong1A-Pi9-1 was proved the best possessing complete and stable sterility,high stigma exsertion rate（74.82%）,low enclosed spikelet rate（29.92%）and excellent agronomic yield traits.4.Seedling blast resistance of both parental and improved rice lines was investigated through greenhouse inoculation and field nursery assays.75-1-127 showed high-level resistance（0 grade）while two receptor parents was highly susceptible（4⁵ grades）,and eight improved CMS lines and their maintainers showed identical blast resistance to the donor parent in field nursery.Resistance responses to fifteen tested M.oryzae isolates were quite different between 75-1-127 and two receptors,presenting 86.67%and 6.67%resistance frequency respectively.Taonong 1A-Pi9-1 and Taonong 1B-Pi9-1 shared the same resistance spectrum with 75-1-127.These results showed that seedling blast resistance of Taonong 1A and Taonong 1B was successfully improved through MAS breeding practice.