| Rice is an important food crop.Rice blast is one of the most destructive diseases affecting rice production,and resistance breeding is believed the most economical and effective measure to minimize the damage by this disease.To directionally improve blast resistance of the rice CMS line Fengyuan A and its maintainer Fengyuan B,consecutive backcross breeding practice was implemented through molecular marker-assisted election（MAS）of the broad-spectrum and durable blast resistance gene Pi9.In this study,the indica rice line 75-1-127 haboring the Pi9 gene,was employed as the donor parent,Fengyuan B and Fengyuan A as the receptor parents respectively,DNA markers were designed according to Pi9 sequence and polymorphic marker was screened using genomic template of both donor and receptor parents.The main results were as follows:1.Blast resistance of parental rice lines was investigated by means of greenhouse inoculation and field nursery assays.Resistance responses to 33 tested M.oryzae isolates showed big difference between 75-1-127 and Fengyuan A and its maintainer Fengyuan B,presenting 87.9%and 33.3%resistance frequency respectively,and overlapping resistance-spectrum was observed between the donor and receptors.In natural nursery,75-1-127 showed high-level seedling blast resistance（0 grade）but highly susceptible（4～5grades）for two receptor parents.These results showed that the Pi9 gene is promising in rice blast resistance breeding,and blast resistance of two receptors needs to be improved urgently.2.Six molecular markers were developed based on DNA sequence information of the Pi9 gene,and one of them,CLONDF1R1,showed obvious and stable polymorphism between donor/receptor parents.The CLONDF1R1 marker primers amplified a 320bp band from the genome of 75-1-127 while PCR product from two receptors is nearly 450bp,so PCR products by this codominant marker can be simply and quickly checked by agarose gel electrophoresis.3.The codominant molecular marker CLONDF1R1 was used in MAS backcross breeding practice for improving blast resistance of Fengyuan B and Fengyuan A respectively.Thirteen maintainer lines Fengyuan B-Pi9,and eleven CMS lines Fengyuan A-Pi9,carrying the Pi9 homozygous alleles and showing high-level seedling blast resistance,were developed.4.Sterility and cross-pollination traits of partial Fengyuan A-Pi9 lines,main agronomic and yield traits of partial Fengyuan A-Pi9 and Fengyuan B-Pi9 lines were investigated by field assays,and an elite CMS line Fengyuan A-Pi9-5 and its maintainer Fengyuan B-Pi9-5were bred.Fengyuan A-Pi9-5 showed high-level seedling blast resistance,complete male sterility,high stigma exsertion rate（65.6%）,improved agronomic and yield traits.Thus,we achieved the goal to directionally improve blast resistance of rice CMS line Fengyuan A and its maintainer Fengyuan B,and created a set of new parents for three-line method hybrid rice breeding application. |
