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1.
Mahsuri a popular traditional variety and the first rain-fed mega variety of the Indian sub- continent. It is highly susceptible to bacterial leaf blight caused by Xanthomonas oryzae pv.oryzae. Nine best performing families of Mahsuri pyramid containing four bacterial blight resistance genes (Xa4, xa5, xa13 and Xa21) were evaluated for agronomic, yield and its related characters viz. days to 50% flowering, plant height, number of tillers, panicle length, filled grains per panicle, grain weight, and yield under natural and disease pressure conditions for three consecutive wet seasons. In addition these pyramids were also evaluated for three different spacings to find out the optimum spacing under disease free and disease pressure conditions. Results revealed that under disease free conditions there was no significant difference between the pyramids and the parent for the characters evaluated in each spacing. However characters plant height, number of tillers, panicle length, filled grains per panicle, yield per plant and yield per sq. m. showed significant variation between the different spacings across seasons. Under heavy disease pressure the parent exhibited highly susceptible reaction whereas the pyramid families were highly resistant. A wider spacing had less yield loss when compared to dense planting under BB infestation in case of parent. There was no such yield loss in the pyramid families. When yield per sq. m. was taken into consideration the 20 × 20 cm spacing showed the highest yield when compared to the other two spacings since number of plants were more. The pyramids insulated the yield loss against bacterial leaf blight and are a gain to the farmers to help overcome the heavy yield losses due to this disease. These pyramids have the potential to replace the parent and can be used directly. In addition they can be used as donors for bacterial blight resistance in any breeding program.  相似文献   

2.
Bacterial blight, caused by Xanthomonas oryzae pv. oryzae (Xoo) is a destructive disease of rice in the major rice growing countries of Asia. In 2003, a serious bacterial blight epidemic occurred in the southwestern coastal areas in Korea, causing significant yield loss due to the emergence of a new race, K3a. IR24 near-isogenic lines containing Xa4, xa5, Xa7 and Xa21 genes conferred different degrees of resistance to the most virulent K3a isolate, HB01009 in an inoculation experiment in the greenhouse. Expression levels of the resistance genes, Xa4, xa5 and Xa21 were studied in two F2 populations derived from the crosses between elite japonica cultivars and an advanced backcross breeding line possessing Xa4, xa5 and Xa21 genes. F2 progenies segregated for K3a resistance (R) and susceptible (S) phenotypes in a ratio of 3(R):1(S) indicated that K3a resistance was controlled by a major dominant gene. Three PCR markers tightly linked to the resistance genes Xa4, xa5 and Xa21 confirmed the presence of the genes and their interaction with each gene. This study demonstrated that the Xa21 gene dominantly contributed to K3a resistance. However, the Xa4 gene also contributed to the full expression of resistance. The level of expression of strong resistance to K3a race was attributed to the presence of Xa21 and Xa4 genes irrespective of the presence of xa5 gene. Our results suggest that the R-gene combinations of Xa4+Xa21 could be a useful and effective strategy toward improving resistance to K3a race of Korean japonica cultivars.  相似文献   

3.
Samba Mahsuri (BPT5204) is a medium slender grain indica rice variety that is very popular with farmers and consumers across India because of its high yield and excellent cooking quality. However, the variety is susceptible to several diseases and pests, including bacterial blight (BB). We have used PCR based molecular markers in a backcross-breeding program to introgress three major BB resistance genes (Xa21, xa13 and xa5) into Samba Mahsuri from a donor line (SS1113) in which all the three genes are present in a homozygous condition. At each backcross generation, markers closely linked to the three genes were used to select plants possessing these resistance genes (foreground selection) and microsatellite markers polymorphic between donor and recurrent parent were used to select plants that have maximum contribution from the recurrent parent genome (background selection). A selected BC4F1 plant was selfed to generate homozygous BC4F2 plants with different combinations of BB resistance genes. The three-gene pyramid and two-gene pyramid lines exhibited high levels of resistance against the BB pathogen. Under conditions of BB infection, the three-gene pyramid lines exhibited a significant yield advantage over Samba Mahsuri. Most importantly, these lines retain the excellent grain and cooking qualities of Samba Mahsuri without compromising the yield as determined in multi-location trials. This work demonstrates the successful application of marker-assisted selection for targeted introgression of multiple resistance genes into a premium quality rice variety. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. R. M. Sundaram and M. R. Vishnupriya have contributed equally to this work.  相似文献   

4.
J. Zhang    X. Li    G. Jiang    Y. Xu    Y. He 《Plant Breeding》2006,125(6):600-605
‘Minghui 63’ is a restorer line widely used in hybrid rice production in China for the last two decades. This line and its derived hybrids, including ‘Shanyou 63’, are susceptible to bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo). To improve the bacterial blight resistance of hybrid rice, two resistance genes Xa21 and Xa7, have been introgressed into ‘Minghui 63’ by marker‐assisted selection and conventional backcrossing, respectively. The single resistance gene‐introgressed lines, Minghui 63 (Xa21) and Minghui 63 (Xa7) had higher levels of resistance to bacterial blight than their derived hybrids, Shanyou 63 (Xa21) or Shanyou 63 (Xa7). Both Xa21 and Xa7 showed incomplete dominance in the heterozygous background of rice hybrids by infection with GX325 and KS‐1‐21. The improved restorer lines, with the homozygous genotypes, Xa21Xa21 or Xa7Xa7, were more resistant than their hybrids with the heterozygous genotypes Xa21xa21 or Xa7xa7. To further enhance the bacterial blight resistance of ‘Minghui 63’ and its hybrids, Xa21 and Xa7 were pyramided into the same background using molecular marker‐aided selection. The restorer lines developed with the resistance genes Xa21 and Xa7, and their derived hybrids were evaluated for resistance after inoculation with 10 isolates of pathogens from China, Japan and the Philippines, and showed a higher level of resistance to BB than the restorer lines and derived hybrids having only one of the resistance genes. The pyramided double resistance lines and their derived hybrids have the same high level of resistance to BB. These results clearly indicate that pyramiding of dominant genes is a useful approach for improving BB resistance in hybrid rice.  相似文献   

5.
Basmati rice is highly susceptible to bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae. Transfer of BB resistance genes from non‐Basmati sources to Basmati through cross‐hybridization requires strict monitoring for recovery of the desirable Basmati quality traits in the recombinants, which show complex inheritance pattern. We integrated background analysis using mapped microsatellite markers with foreground selection to identify superior lines that combine useful genes from a non‐Basmati BB resistance donor line IRBB55 with grain and cooking quality characteristics of the popular Basmati rice variety ‘Pusa Basmati 1’ (PB 1) employing backcross pedigree strategy. Foreground selection using linked markers ensured presence of two genes, xa13 and Xa21 for BB resistance from IRBB55, and the recurrent parent PB 1 allele for the waxy locus giving intermediate amylose content and maintainer allele at fertility restorer locus in the BC1F5 recombinants. Background analysis enabled selection of recombinants with recurrent parent genome to the extent of 86.3% along with the quality traits. The extent of introgression of non‐Basmati donor chromosome segments in the superior selections was estimated to be < 7.8 Mb and < 6.7 Mb in the xa13 and Xa21 linked genomic regions, respectively. Association mapping identified three quantitative trait loci, one each for 1000‐grain weight, fertile grains/panicle and cooked kernel length. The backcross‐pedigree breeding strategy facilitated recovery of additional desirable characteristics from the donor in some of the selections. The elite selection Pusa 1460‐01‐32‐6‐7‐67 with maximum genomic background and quality characteristics of the recurrent Basmati parent gave resistance reaction against BB, similar to that of the non‐Basmati resistant check variety and recorded an yield advantage of 11.9% over the best check in the multiplication agronomic trial in the Basmati growing region of India. This line, which has been released as a new variety in the name of ‘Improved Pusa Basmati 1’ for commercial cultivation in India, is an example of successful application of marker assisted selection to variety development.  相似文献   

6.
A traditional Type 3 Basmati rice cultivar grown in India is tall and lodges even under low nitrogen fertilizer dose. In addition to lodging, it is highly susceptible to several diseases and pests including bacterial blight (BB). BB resistance genes (Xa21 and xa13) and a semidwarfing gene (sd-1) were pyramided in Type 3 Basmati from a rice cultivar PR106-P2 using marker-assisted selection (MAS). Foreground selection for BB resistance genes, Xa21 and xa13 and reduced plant height gene, sd-1 was carried on the basis of linked molecular markers pTA248, RG136 and ‘h’, respectively. The BC2F3 progenies with both the BB resistance genes were highly resistant with lower lesion length than either of the genes individually. Background profiling of the selected 16 BC2F3 progenies was done using 95 anchored SSR and 12 ISSR markers. Among the selected 16 BC2F3 progenies, 38-5-2 and 38-5-36 closely clustered along with the recipient parent Type 3 Basmati showing above 85% genetic similarity with the same. Further selection was continued till F5 generation for higher recovery for Type 3 Basmati characteristics. The desirable alleles of intermediate amylose content (wx) and aroma (fgr) loci of Type 3 Basmati were also tracked using the linked SSR markers. The BC2F5 pyramid lines T3-4, T3-5, T3-6 and T3-7 homozygous for the three target genes Xa21, xa13 and sd-1 from the donor parent with wx and fgr alleles of Type 3 Basmati had excellent cooking quality and strong aroma.  相似文献   

7.
Forty resistant rice cultivars were studied for theinheritance of resistance to bacterial blight usingPhilippine races of Xanthomonas oryzae pv.oryzae (Xoo). Results showed that all thevarieties have at least two recessive genes forresistance. One of these genes governs resistance torace 1 (PXO61) while the other gene confers resistanceto race 6 (PXO99). In addition to the recessivegenes, nine of the varieties possess another dominantgene which also confers resistance to race 1.Allelism tests revealed that the recessive genesgoverning resistance to race 1 in 39 varieties areallelic to xa5 while the dominant genes in thenine varieties are allelic to Xa4. Therecessive gene conferring resistance to race 1 incultivar Sada Diga is inherited independently of xa5. Similarly, the recessive genes governingresistance to race 6 in all the varieties arenon-allelic to xa13. The allelic relationshipsof these genes with xa-24(t), a new recessivegene identified in cultivar DV86 which conveysresistance to race 6 are now being investigated.  相似文献   

8.
In this paper, we described the breeding of transgenic rice restorer line for multiple resistance against bacterial blight, striped stem borer (SSB) and herbicide by conventional crossing of two transgenic parental lines transformed independently with different genes. Two stable transgenic rice lines used as donor parents were developed, one was Zhongguo91 which contained cry1Ab gene (for insect resistance) and bar gene (for tolerance of herbicide), and the other was Yujing6 which contained Xa21 gene (resistance to bacterial blight). The elite restorer line Hui773 was used as recipient and crossed with the two stable transgenic rice lines. Then five successive backcrosses were made using Hui773 as recurrent parent. Two rice elite restorers, T773-1 expressing cry1Ab and bar genes and T773-2 expressing Xa21 gene, were obtained, which were confirmed by PCR analysis and testing selectable marker genes in the hybrid progenies. The cross was made between T773-1 and T773-2 to select stable restorer line carrying Xa21, cry1Ab and bar genes. Finally, we obtained transgenic restorer line T773 with good agronomic traits and obvious multiple resistance to Xanthomonas oryzae pv. oryzae, striped stem borer (Chilo suppressalis) and herbicide. The hybrid F1 generation produced from the cross between transgenic restorer line T773 and a corresponding male sterile line Zaohua2A maintained obvious resistance to rice bacterial blight, rice leaffolder and striped stem borer, and showed significant heterosis. Our results indicate that it is feasible to develop transgenic hybrid rice cultivar through breeding transgenic restorer lines.  相似文献   

9.
Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is an important disease constraining rice (Oryza sativa L.) production worldwide. The XM6 line was induced by N-methyl-N-nitrosourea from IR24, an Indica cultivar that is susceptible to Philippine and Japanese Xoo races. XM6 was confirmed to carry a recessive gene named xa20, resistant to six Philippine and five Japanese Xoo races. The chromosomal gene location was found using 10 plants with the shortest lesion length in an F2 population consisting of 298 plants from a susceptible Japonica variety Koshihikari × XM6. Analysis using PCR-based DNA markers covering the whole rice genome indicated the gene as located on the distal region of the long arm of chromosome 3. The IKC3 line carries IR24 genetic background with Koshihikari fragment on chromosome 3 where a resistance gene was thought to be located. The F2 population from IKC3 × XM6 clearly showed a bimodal distribution separating resistant and susceptible plants. Further linkage analysis conducted using this F2 population revealed that xa20 is located within the 0.8 cM region flanked by DNA markers KIC3-33.88 (33.0 Mb) and KIC3-34.06 (33.2 Mb). This study yields important findings for resistance breeding and for the genetic mechanism of Xoo resistance.  相似文献   

10.
DNAs of 693 isolates of bacterial blight pathogen of rice, Xanthomonas oryzae pv. oryzae (Xoo), were characterized using PCR-based primers pJEL1 and pJEL2. The pathogen populations were grouped into 97 haplotypes based on DNA-banding patterns. An un-weighted pair-group method using arithmetic averages (UPGMA) indicated a high level of diversity in the pathogen isolates (51 lineages of Xoo at a 70% similarity level). Among these, lineages 5, 7, 27, and 29 are widely distributed and others are localized in the northern region of India. The isolates represent lineage-27, were prevalent in the entire disease-prone area in the region except at Ferozepur. Pathotyping data of the representative isolates of each lineage also indicate 17 different reaction patterns on a set of isogenic lines. Resistance genes xa8 and Xa21 were the most effective followed by xa5, and Xa7 against Xoo isolates prevalent in northern India. Different genes in combinations (xa5+xa13, xa5+Xa21, xa13+Xa21, and xa5+xa13+Xa21) in IR24 genetic background provided better protection against all the pathogen isolates tested in this study than did the component genes. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
Bacterial blight (BB) is the most economically damaging disease of rice in Asia and other parts of the world. In this study, a multiplex PCR genotyping method was developed to simultaneously identify genotypes of five BB resistance genes, Xa4, xa5, Xa7, xa13 and Xa21. The resistance R alleles were amplified using five functional markers (FMs) to generate amplicons of 217, 103, 179, 381 and 595 bp in IRBB66. Amplicons of 198, 107, 87, 391 and 467 bp corresponded to susceptible alleles in Taiwanese japonica rice cultivars. In backcross breeding programmes, the multiplex PCR assay was integrated into selection from a population using BB resistance donor IRBB66 crossed to rice cultivar ‘Tainung82’. Two plants with homozygosity for Xa4, xa5, Xa7, xa13 and Xa21 were selected from 1100 BC2F2 plants. In addition, the five BB resistance genes were also accurately identified in F2 populations. This multiplex PCR method provides a rapid and efficient method for detecting various BB resistance genes, which will assist in pyramiding genes to improve durability of BB resistance in Taiwanese elite rice cultivars.  相似文献   

12.
S. Chen    C. G. Xu    X. H. Lin  Q. Zhang 《Plant Breeding》2001,120(2):133-137
Bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (X00), is one of the most devastating diseases of rice world‐wide; it is also a serious problem of hybrid rice production in China. In this study, a molecular marker‐assisted introgression of Xa21, a gene highly resistant to a broad spectrum of Xoo strains, from ‘IRBB21’ was performed to improve the BB resistance of‘6078′, a new restorer line with high yielding potential. The entire process took one generation of crossing followed by three generations of backcrossing and one generation of selfing. The presence of Xa21 in each generation was determined by both polymerase chain reaction (PCR) and pathogen inoculation. Recombinations between Xa21 and flanking markers were identified by PCR analysis. Background selection was conducted in BC1F1 and BC2F1 using amplified fragment length polymorphism (AFLP) markers detecting a total of 129 polymorphic bands between‘6078’ and ‘IRBB21′. The individual selected in BC3F2, or‘6078′(Xa21), carried a fragment of less than 3.8 cM from the donor line in the Xa21 region on chromosome 11, and about 98.8% of the genetic background from the recurrent parent. The results showed that‘6078′(Xa21) had the same level and spectrum of BB resistance as the donor parent ‘IRBB21′, while maintaining the agronomic performance and combining ability of the original 6078. A significant increase in BB resistance was also achieved in the hybrid using 6078(Xa21) as the restorer line.  相似文献   

13.
B. Huang  J. Y. Xu  M. S. Hou  J. Ali  T. M. Mou 《Euphytica》2012,187(3):449-459
Four bacterial blight (BB) resistance genes, Xa7, Xa21, Xa22 and Xa23, were introgressed into an elite hybrid rice restorer line Huahui 1035, by marker-assisted selection (MAS). Ten promising BB resistant lines identified by MAS approach in Huahui 1035 restorer background and their respective F1 hybrids with a cytoplasmic male sterile line i.e. Jinke 1A, three BB resistant gene donors and their recurrent parent were evaluated for BB resistance by inoculating them with eleven representative races of Xanthomonas oryzae pv. oryzae (Xoo) in China. Further, the ten marker assisted selection of BB (MAS-BB) resistant restorer lines and their F1 hybrids were also characterized for agro-morphological traits and grain yield. Results revealed that restorer lines with Xa23 introgression i.e. HBQ809 and HBQ810 were found to be resistant to all eleven Chinese representative Xoo races, showing broad spectrum resistance to BB. However, the lines possessing Xa7 or Xa7+Xa21 were resistant to ten out of eleven Xoo races. While restorer lines with Xa21 were resistant to nine out of eleven Xoo races. Interestingly, the F1 hybrids with Xa23, Xa7 or Xa7+Xa21 were resistant to two severe epidemic Xoo races of China. Restorer lines i.e. HBQ807 and HBQ808 possessing Xa22 were only resistant to six or five out of inoculated eleven Xoo races. Lesion length comparisons between restorer lines and their F1 hybrids for the above four BB resistance genes showed them to be dominant in heterozygote genotype. Three promising high yielding F1 hybrids with BB resistance were identified for immediate exploitation for hybrid rice production in China.  相似文献   

14.
Bacterial blight (BB) of rice caused by X. oryzae pv. oryzae is a major production constraint in commercial hybrid rice production in the Philippines because most of the parental lines used in hybrid production do not carry resistance genes against the pathogen. In this study, three bacterial blight resistance genes, Xa4, Xa7 and Xa21, were introgressed to a temperature-sensitive genetic male sterile (TGMS1) line. A three-way cross of AR32-19-3-3/TGMS1//IRBB4/7 (PR36944) was made to produce 1,364 F2 plants carrying various combinations of Xa4, Xa7 and Xa21. Individual plants were characterized for reaction to bacterial blight PXO61 (race 1), PXO86 (race 2), PXO99 (race 6) and pollen sterility. Of 144 F2 plants demonstrating resistance against PXO61, PXO86 and PXO99, 22 exhibited highly resistant phenotypes with mean lesion lengths ranging from 0.37–2.97 cm. Analysis of disease reaction identified 20 potential TGMS F2 plants containing Xa4, Xa7 and Xa21 while 78 plants with Xa4 + Xa7. Phenotypic and polymerase chain reaction (PCR) analyses confirmed PR36944-450, PR36944-473 and PR36944-700 as homozygous for Xa7 and Xa21 and highly resistant to all three Xoo races. Fertility of PR36944-450 and PR36944-700 was restored at permissive temperature in a growth chamber. BB-resistant TGMS lines should facilitate breeding two-line hybrids in the tropics.  相似文献   

15.
It has long been known that a bacterial leaf blight-resistant line in rice obtained from a crossing using ‘Asominori’ as a resistant parent also has resistance to blast, but a blast resistance gene in ‘Asominori’ has not been investigated in detail. In the present study, a blast resistance gene in ‘Asominori’, tentatively named Pias(t), was revealed to be located within 162-kb region between DNA markers YX4-3 and NX4-1 on chromosome 4 and to be linked with an ‘Asominori’ allele of the bacterial leaf blight resistance gene Xa1, tentatively named Xa1-as(t). An ‘Asominori’ allele of Pias(t) was found to be dominant and difference of disease severity between lines having the ‘Asominori’ allele of Pias(t) and those without it was 1.2 in disease index from 0 to 10. Pias(t) was also closely linked with the Ph gene controlling phenol reaction, suggesting the possibility of successful selection of blast resistance using the phenol reaction. Since blast-resistant commercial cultivars have been developed using ‘Asominori’ as a parent, Pias(t) is considered to be a useful gene in rice breeding for blast resistance.  相似文献   

16.
水稻抗白叶枯病基因的聚合育种   总被引：7，自引：1，他引：7  
白叶枯病是严重危害水稻生产的重要病害之一,利用聚合多个抗性基因的水稻品种是控制该病害的有效途径。本研究以携带Xa4、xa5、xa13、Xa214个抗白叶枯病基因的IRBB60与8个水稻新品系,组配8个杂交组合.应用分子标记辅助选择技术从F2和F3群体中共获得216个携带4个抗白叶枯病基因的纯合体。用华南地区的5个白叶枯病病原菌小种进行田间接种的试验表明,4个抗性基因聚合系的抗性水平高于只带1个抗性基因的近等基因系。这些聚合系可用作华南地区高抗白叶枯病水稻品种育种的亲本材料。  相似文献   

17.
Two‐line hybrid rice technology is an effective way to increase rice production and improve rice quality. In this study, three bacterial blight (BB) resistance genes, Xa7, Xa21 and Xa23, were introgressed separately into C815S, a popular thermo‐sensitive genic male sterile (TGMS) line to develop five BB‐resistant lines (Hua1005S, Hua1002S, Hua1009S, Hua1006S and Hua1001S) to be resistant against seven races of Xanthomonas oryzae pv. oryzae (Xoo). The two‐line hybrids with heterozygous Xa23 were resistant against seven Xoo strains. But, the hybrids with heterozygous loci for both Xa7 and Xa21 were only resistant against three Xoo strains and were moderately susceptible to the other four strains indicating the role of modifiers influencing the poor expression of dominant BB resistance genes under heterozygous state. Among them, Hua1006S was found to be a promising TGMS line with its higher degree of disease resistance level on account of broad‐spectrum resistance gene Xa23 besides possessing better plant type and rice grain quality features.  相似文献   

18.
Functional markers reduce the risk of false selection in marker-assisted selection (MAS), and recombination between the molecular marker and the gene of interest. The present study was conducted with the objective of combining the important basmati quality traits with resistance to bacterial leaf blight (BLB) by a combination of phenotypic selection and MAS. Screening of 29 recombinants for BLB resistant genes along with aroma (fgr) gene was performed using a suite of different markers. Twenty genotypes were found in homozygous condition for Xa21 and xa13 genes. Restriction digestion analysis with BsrI, gave nine resistant recombinants. Out of nine resistant recombinants, seven were in homozygous and two were in heterozygous conditions. Recombinants viz., IRS 5441-2-21, IRS 5441-2-79, IRS 5441-2-81, IRS 5441-2-85 and IRS 5441-2-91 possessed all the three BLB resistance genes and fgr in the homozygous condition. Recombinants with enhanced resistance to BLB, basmati quality and desirable agronomic traits were identified. This germplasm can be directly developed into commercial varieties or used as immediate potential donors of BLB resistance in basmati breeding programs.  相似文献   

19.
Bacterial leaf blight (BB) is among the “top 3” diseases in rice production. Breeding resistant cultivars has been the most effective strategy for BB management. The inbred cultivar Baixiangzhan (BXZ) showed a broad spectrum of resistance to five Xoo pathotypes in China, including the prevalent and highly virulent Xoo pathotypes Chinese Race V (CV), which can overcome the resistance of Xa4 and Xa21. The resistance heredity of BXZ has been explored in this study. A single recessive major resistance gene, which designated as xa42(t), confers resistance against the tested Xoo pathotypes CV. Linkage analysis lands xa42(t) on chromosome 6, and genetic mapping confines it to 3.9 cM region flanked by RM20558/RM20547 and RM20580. A further seven markers were developed from this interval for high‐resolution mapping, and the xa42(t) locus was narrowed to 34.8 Kb segment bounded by RM20572 and DT46. The only functionally predicted gene included in the target region is LOC_Os06g45960 if based on the ‘Nipponbare’ reference sequence. This candidate gene is predicted to encode a cytochrome P450 protein.  相似文献   

20.
IR 58025A is a very popular wild‐abortive cytoplasmic male sterile (WA‐CMS) line of rice and is extensively used for hybrid rice breeding. However, IR 58025A and many hybrids derived from it possess mild aroma (undesirable in some parts of India) and are highly susceptible to bacterial blight (BB) and blast diseases. To improve IR 58025A for BB and blast resistance, we have introgressed a major dominant gene conferring resistance against BB (i.e. Xa21) and blast (i.e. Pi54) into IR 58025B, the maintainer line of IR 58025A. An introgression line of Samba Mahsuri (i.e. SM2154) possessing Xa21 and Pi54 genes in homozygous condition and fine‐grain type was used as donor parent, and backcross breeding strategy was adopted for targeted introgression of the resistance genes. PCR‐based molecular markers tightly linked to Xa21 and Pi54 were used for selection of BB‐ and blast‐resistant lines, while closely linked markers were used for identification of backcross‐derived plants devoid of Rf4 and aroma. At BC2F5, four backcross‐derived lines possessing resistance against BB and blast, devoid of aroma, high yield, short plant stature, long‐slender grain type and with recurrent parent genome recovery ranging from 88.8% to 98.6% were selected and advanced for further evaluation. The improved versions of IR 58025B, viz. SB54‐11‐143‐9‐44‐5, SB54‐11‐143‐9‐44‐98, SB54‐11‐143‐9‐44‐111 and SB54‐11‐143‐9‐44‐171, behaved as perfect maintainers when test‐crossed with WA‐CMS lines. Agronomically superior lines of improved IR 58025B are being converted to CMS line through backcrossing for developing high‐yielding and biotic stress‐resistant rice hybrids.  相似文献   

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