Improvement Of The Bacterial Blight Resistance Of Hua201S And Huahui2185

Bacterial blight(BB) of rice is one of the most destructive diseases throughout the world,and one of three rice important diseases in china.It reduces yield and the quality of the rice grains and affects stability of rice production seriously.BB is major production constrsaint in rice production in the Asia,particularly in hybrid rice in China,because of many parental lines without resistance genes of the pathogen.The exploitation of host resistance and incorporation of resistance genes into cultivars is the most economical, effective means of controlling the disease.With the development of genetic and molecular biological technology,molecular marker assisted selection(MAS) breeding has been a efficient and practical method for the improvement of various traits.The objectives of this study was to use MAS method in the process of the conventional crossing-backcrossing to introgress BB resistance gene Xa7 or Xa21 into two elite rice parents,Hua201S and Huahui2185,which were photo-thermo-sensitive genic male sterile line and restorer line, respectively.The main results are as follows:1.Two BB resistance Xa21 and Xa7 were introgressed to recurrent parent Hua201S. Four breeding lines have been developed by using molecular marker assisted selection. The agronomic traits of four lines were stable and similar to Hua201S,the recurrent parent.The result of resistance identification in field showed that the lesion length in the breeding lines with Xa21 gene was 0.6-2.0 cm for PXO61,0.5-2.3 cm for ZHe173 and 1.2-6.7 cm for PXO99.The lesion length in the lines Xa7 gene was 0.5-5.8cm for PXO61 and 0.5-3.5cm for ZHe173.The levels of resistance to BB reached middle grade and were obviously higher than that of recurrent parent Hua201S.2.The new photo-thermo-sensitive genic male sterile lines with BB resistance gene were selected from different segregation generation.The result of resistance identifcation in field showed that the lesion length of new lines with Xa21 gene was 0.6-2.2 cm for PXO61,1.0-2.6 cm for ZHe173 and 1.7-4.1 cm for PXO99.The lesion length of the lines with Xa7 gene was 1.4-7.5 cm for PXO61 and 0.9-4.1cm for ZHe173.Their resistance reached middle level.3.BB resistance gene Xa7 and Xa7 from the donor parent,Huahui20,were introgressed into Huahui2185,a restorer line through backcrossing and MAS method.Two breeding lines with Xa21 and two lines with Xa7 were selected from 34 BC₃F₃ lines.The inoculation with BB strain,ZHe173 showed that the mean lesion length of YR6086 (Xa21) was 1.87cm,YR6092(Xa21) was 1.79 cm,YR6107(Xa7) was 1.18 cm, YR6109(Xa7) was 0.57 cm.Their agronomic traits were similar to Huahui2185.4.Two plants were selected from each BC₃F₃ line.Their seeds were planted in winter season and seeds of BC₃F₄ plants were harvested in spring season,2007 at Lingshui, Hainan Province.BC₃F₅ lines and their hybrids were inoculation with PXO61 PXO99 and ZHe173 in field at Wuhan in summer season,2007.The results of identification showed that the resistance and resistance spectrum to BB were better than Huahui2185 and its hybrid. 5.The analysis of rice quality and combining ability indicated that YR6092-5 was similar to the recurrent parent,Huahui2185,in the main agronomic traits and their GCA effects.The yield GCA effect of YR6107-2 was better than Huahui2185.The growth duration,seed setting rate and thousand grain weight(g) of YR6086-18 were difference from Huahui2185 significantly.But its yield SCA variance value was higher than Huahui2185.6.Two heterotic combinations,Hua108A/YR6086-18 and 600A/YR6086-18 were selected through heterosis analysis.Their yields were 36.8%and 11.8%over contronl hybrid,â…¡-You 838,with similar growth duration.