Improvement Of The Resistance Of Rice Restorer Line Xiang5 And Development Of Ptgms Lines With Multi-resistance

Two-line hybrid rice has been used in rice production in China for more than three decades,and has become one of the main types of hybrid rice in China due to its advantages such as more freedom to select elite hybrid combinations and more simple process of seed production.Compared with three-line hybrid rice,the resistance of two-line hybrid rice to rice blast,brown planthopper(BPH)and bacterial blight(BB)has not been significantly improved which still needs to be improved.Molecular marker assisted selection(MAS)provides an effective method to improve disease and insect resistance of specific varieties rapidly and accurately.In this study,we use several major resistance genes to improve the resistant against rice blast,BPH and BB in a restorer line,Xiang5,and a photo-thermo-sensitive genic male sterile(PTGMS)line,Longke638S(LK638S),through MAS and phenotypic selection approaches.The main results are as follows:1.Xiang5,a two-line hybrid rice fragrant restorer line,used as recurrent parent was crossed with MD12086-1351 carring Pi9,Bph14,Bph15 and Xa23 as donor parent.Three improved restorer lines carrying homozygous Pi9,Bph14,Bph15 and Xa23 under the genetic background of Xiang5 were developed through marker-assisted backcrossing(MABC)coupled with phenotypic selection,finally designated as STQ15035-53-39-10-10,STQ15035-53-97-2 and STQ15035-53-176-5,respectively.The resistance spectrum identification of rice blast showed that the resistance frequency of the improved lines ranged from 90.91% to 95.45%,while Xiang5 was only 27.27%.The evaluation results under natural blast epidemic field conditions showed that the improved lines with a score 4 for leaf blast,obviously enhanced resistance level compared with Xiang5,but there was no significant difference in panicle blast.The identification of resistance to BPH in seedling stage showed that the improved lines were resistant against BPH with damage scales ranged from 3.0 to 5.4,were obviously slighter than Xiang5 with a scale of 8.7.When infected with bacterial blight strains GD1358 and ZHE173,the improved lines showed highly resistant against these Xoo strains,their lesion length was 0.6-1.5cm which was significantly shorter than Xiang5 with lesion length of 12.0cm-23.8cm.The evaluation results of major agronomic traits and grain qualities showed that there were few significant differences between the improved lines with the recurrent parent Xiang5.Moreover,the hybrids derived from the improved lines also exhibited similar agronomic performance and rice quality compared with the controls under natural field conditions.Therefore,the improved lines can be used as an alternative to Xiang5 for breeding two-line hybrid rices conferring resistant against rice blast,BPH and BB.2.An elite PTGMS line,LK638 S as the female parent was crossed with a PTGMS breeding line,DB1501-98,carring Pi2,Bph14,Bph15 and Xa23.Through MAS,fertility identification coupled with phenotypic selection,we selected out five PTGMS lines carrying homozygous Pi9,Bph14,Bph15 and Xa23 from offspring of LK638S/DB1501-98,named Hua8049 S,Hua8050S,Hua8051 S,Hua8053S,and Hua8054 S.The results of resistance identification showed that five PTGMS breeding lines were resistant or highly resistant against BPH with damage scales from 1.2 to 3.4,were obviously slighter than LK638 S.LK638S was susceptible or highly susceptible to Xoo strains with the lesion length over 19 cm,while the five PTGMS breeding lines were resistant or highly resistant against Xoo strains.The leaf blast scores and panicle blast incidences of the five PTGMS breeding lines were less than 4 and 20%,respectively,conferred significantly enhanced resistance compared with LK638 S.The five PTGMS breeding lines possessed stable sterility periods of 60-80 days under natural field conditions and their critical temperature point of fertility-sterility alteration may be slightly higher than 24? of daily mean temperature.Agronomic performance of five PTGMS breeding lines showed that the stigma exsertion rate of Hua8050 S was the highest(69.54%),while the lowest(19.33%)was Hua8054 S,and other PTGMS lines ranged from 32.81%-59.17%.Compared with LK638 S,the plant height and growth duration of five PTGMS breeding lines reduced and shortened,respectively,but their spikelets per panicle decreased.In terms of rice grain qualities,except for low amylose content of some lines,the other indexes of the PTGMS breeding lines reached the national high quality paddy grade 2 standard or higher.The analysis results of combining ability showed that general combining ability of parents largely determined the performance of hybrid combinations in major agronomic traits.With Hua8050 S as female parent,the combinations have early-maturity,dwarfer plant,more spikelets per panicle and good seed setting rate.With Hua8051 S as female parent,the combinations have early-maturity,dwarfer plant,strong tillering ability and high yield.