Genes Xa21 Research Articles

Marker Assisted Selection in Advanced Backcross Population of Rice Variety, MTU1010 for Bacterial Blight and Blast Resistance

The present study was aimed for identification of the bacterial blight and blast resistant lines in the advanced back cross population of MTU-1010 using marker assisted foreground selection and also for evaluation of agro-morphological characters. The M-16-59 introgressed line (derived from an intercrossing of BC2F1 plants of MTU-1010 x GPP2 and MTU-1010 x NLR 145) is developed under ongoing DBTDBSRR subproject -IV possessing Xa21, xa13, Pi1 and Pi54 resistance genes having broad spectrum resistance to bacterial blight and blast is used as a donor parent and MTU-1010 was used as a recurrent parent for the back cross. Before attempting the backcross both the parents were verified for the target genes along with the original donors GPP2 and NLR 145 using gene specific/linked molecular markers viz., xa13-promo for xa13 gene, pTA248 for Xa21 gene, RM 224 for Pi1 and Pi54 MAS for Pi54. under the F1 generation (equivalent to BC3F1 because two backcrosses were completed earlier), 120 plants were screened, and 16 plants were confirmed for xa13, Xa21, Pi1, and Pi54 genes under heterozygous conditions. These confirmed plants were assessed for agro-morphological characteristics such as yield, grain features, and plant type. The results showed that the confirmed heterozygous plants were comparable to MTU-1010 and passed to the next round of selection and evaluation. The BC1F1-198th plant (96.8%) was selfed to produce BC1F2 population. Twenty five plants were advanced to BC1F3 generation based on BB resistance and above other phenotypic characters. The selected BC1F3 progenies were screened for blast and BB resistance. Four BC1F3 progenies with four target genes (xa13xa13Xa21Xa21Pi54Pi54Pi1Pi1) showed very high level of resistance to both the diseases. BC1F2-198-52nd line found similar to MTU1010 with respect to yield and yield related characters besides showing resistance to both BB and blast.Improved lines of MTU1010 can be advanced for multi-location testing under All India Coordinated Rice Improvement Project (AICRIP) for their evaluation and possible release for the benefit of rice farmers.

Pyramiding of multiple resistant genes of blast and bacterial blight diseases in the background of rice (Oryza sativa) mega variety BRRI dhan29

Blast and bacterial blight (BB) are the two major rice diseases in the world including Bangladesh. In this study, BB resistance genes (Xa21 and xa13) and blast resistance (Pi9 and Pb1) genes were pyramided into a mega variety, BRRI dhan29 through marker-assisted backcross breeding. IRBB58 was used as a BB-resistant donor and Pi9-US2, and Pb1-US2 were used as blast-resistant donors. Backcross was done between BRRI dhan29 and donor parents to develop BC3F1 population and then selfing was done to develop BC3F6 population. BC3F2 population was genotyped and phenotyped for segregation analysis and BC3F6 was evaluated for genotyping, phenotyping and morphological traits and yields. Chi-square analysis of BC3F2 data revealed that blast and BB resistance followed the single gene mendelian fashion (1:2:1 and 3:1). Two to four gene combinations were found in the advanced lines of the BC3F6 population. The yield of the advanced lines ranged from 6.42 (t ha-1) to 9.5 (t ha-1) and they showed resistant against blast and BB with mean disease scores ranging from 0.67 to 2.33 and 0.33 to 2.33, respectively. Finally, eight lines having four genes (xa13, Xa21, Pi9 and Pb1) were selected for multilocational (five locations) trials for yield performance and disease reaction. Mean yield data of eight advanced lines of all locations were varied from 6.48±0.15 to 8.38±0.11 t ha-1 and all the lines showed resistant reactions against blast (score 0.53 to 1) and BB (score 0.6 to 0.87) disease. The highest yield was found in BR (Path) 13800-BC3-224-12 (G28, 8.38±0.11 t ha-1) followed by BR (Path) 13800-BC3-134-252 (G26, 8.28±0.08 t ha-1) and BR (Path) 13800-BC3-136-115 (G12, 8.24±0.07 t ha-1). Pyramided advanced lines of this study could be released as BB and blast-resistant varieties or could be utilized as donor parents in resistant breeding.

Development and Validation of an SNP Marker for Identifying Xanthomonas oryzae pv. oryzae Thai Isolates That Break xa5-Mediated Bacterial Blight Resistance in Rice.

Xanthomonas oryzae pv. oryzae (Xoo) is a pathogenic bacterium responsible for bacterial blight (BB) disease in rice, primarily mediated by the interaction between the plant and pathogen. The virulence mechanism involves the activation of the Sugars Will Eventually be Exported Transporter (SWEET) gene family in rice by transcription activator-like effectors derived from Xoo. The BB resistance gene xa5 has been identified as one of the most effective genes against Thai Xoo isolates, but xa5-mediated resistance-breaking Xoo strains have emerged. This study aimed to develop a single nucleotide polymorphism (SNP) marker for precise identification of xa5-mediated resistance-breaking Xoo. Comparative genomics of Thai Xoo isolates Xoo16PK001 and Xoo16PK002, which were incompatible and compatible with rice variety IRBB5 carrying xa5, respectively, identified eight SNP positions for the development of an SNP marker. The SNP marker XooE6 yields a specific 1,143 bp PCR product unique to Xoo16PK002. Screening 61 Thai isolates using XooE6 identified two positives: Xoo20PL010 and Xoo20UT002. Inoculation tests on rice varieties IRBB5 and IRBB13 demonstrated compatibility with IRBB5 and incompatibility with IRBB13, which bears Xa5 and xa13. Xoo16PK001 (XooE6-negative) showed different virulence. Inoculation on IRBB21 harboring Xa5, Xa13, and Xa21 resulted in partial resistance to both XooE6-positive and -negative strains. XooE6-positive strains up-regulated SWEET11 and suppressed SWEET14 in IRBB5, while Xoo16PK001 slightly induced SWEET11 but activated SWEET14 in IRBB13. This highlights the potential of XooE6 to identify xa5-mediated resistance-breaking Xoo strains and elucidate their pathogenic mechanisms through the upregulation of SWEET11.

Stable and robust Xi and Y transcriptomes drive cell-type-specific autosomal and Xa responses in vivo and in vitro in four human cell types

Recent invitro studies of human sex chromosome aneuploidy showed that the Xi ("inactive" X) and Y chromosomes broadly modulate autosomal and Xa ("active" X) gene expression. We tested these findings invivo. Linear modeling of CD4+ Tcells and monocytes from individuals with one to three X chromosomes and zero to two Y chromosomes revealed 82 sex-chromosomal and 344 autosomal genes whose expression changed significantly with Xi and/or Y dosage invivo. Changes in sex-chromosomal expression were remarkably constant invivo and invitro; autosomal responses to Xi and/or Y dosage were largely cell-type specific (∼2.6-fold more variation than sex-chromosomal responses). Targets of the sex-chromosomal transcription factors ZFX and ZFY accounted for a significant fraction of these autosomal responses both invivo and invitro. We conclude that the human Xi and Y transcriptomes are surprisingly robust and stable, yet they modulate autosomal and Xa genes in a cell-type-specific fashion.

Expression profiles of XIK1 and OsSWEET14 genes in parental and back‐ crossing rice lines after Xanthomonas oryzae pv. oryzae infection

Oryza sativa L. ssp. indica (RD47 cultivar) is a major commercial rice variety known for its highly stable yields. However, it is highly susceptible to bacterial blight disease caused by Xanthomonas oryzae pv. oryzae (Xoo). While previous research has focused on improving rice cultivars through breeding programs, no reports involved the interaction between Xoo infection and gene expression. This study aimed to analyze the relationship between bacterial blight disease and gene expression, focusing on two resistance genes (Xa21 and XIK1) and one susceptible gene (OsSWEET14). Gene expression analysis revealed that the Xa21 gene conferred effective resistance against bacterial blight Xoo16PK002 infection, providing high and moderate resistance to bacterial blight symptoms in two rice varieties carrying the Xa21 gene, IRBB21 and the near–isogenic RD47–Xa21 BC4F4, respectively. Additionally, the Xa21 gene directly induced XIK1 expression in both resistance rice cultivars. Moreover, one susceptible gene, OsSWEET14, was consistently up–regulated in only the bacterial blight–susceptible indica rice cultivar RD47. Therefore, the up–regulation of resistance genes and the suppression of susceptible genes contributed to the improvement of bacterial blight disease in the RD47 cultivar. Xa21 emerged as a criti‐ cally important gene in directly inducing mechanisms against Xoo, thereby promoting the reduction of bacterial blight disease.

Pyramiding of bacterial blight resistance genes into promising restorer BRRI31R line through marker-assisted backcross breeding and evaluation of agro-morphological and physiochemical characteristics of developed resistant restorer lines.

BRRI31R is one of the Bangladesh's most promising restorer lines due to its abundant pollen producing capacity, strong restoring ability, good combining ability, high outcrossing rate and genetically diverse from cytoplasmic male sterile (CMS) line. But the drawback of this line is that it is highly susceptible to bacterial blight (BB) disease of rice caused by Xanthomonas oryzae pv. oryzae. The present study highlighted the pyramiding of effective BB resistance genes (xa5, xa13 and Xa21) into the background of BRRI31R, through marker-assisted backcrossing (MABC). Backcross progenies were confirmed and advanced based on the foreground selection of target genes. Pyramided lines were used for pathogenicity test against five Bangladeshi Xanthomonas oryzae (BXo) races (BXo93, BXo220, BXo822, BXo826, BXo887) and confirmed the dominant fertility restore genes, Rf3 and Rf4 and further validated against SNP markers for more confirmation of target resistance genes. All pyramided restorer lines consisted of Xa4 (in built), xa5, xa13, Xa21, and Chalk5 with two fertility restorer genes, Rf3, Rf4. and these restorer lines showed intermediate amylose content (<25%). Restorer lines BRRI31R-MASP3 and BRRI31R-MASP4 showed high levels of resistance against five virulent BXo races and SNP genotyping revealed that these lines also contained a blast resistance gene Pita races. Gene pyramided restorer lines, BRRI31R-MASP3 and BRRI31R-MASP4 can directly be used as a male parent for the development of new BB resistant hybrid rice variety or could be used as a replacement of restorer line of BRRI hybrid dhan5 and 7 to enhance the quality of hybrid seeds as well as rice production in Bangladesh.

Integrative genomic and transcriptomic analysis of Xanthomonas oryzae pv. oryzae pathotype IV, V, and IX in China reveals rice defense-responsive genes

Bacterial blight of rice is a devastating disease caused by the gram-negative bacteria Xanthomonas oryzae pv. oryzae (Xoo). Chinese Xoo strain pathotypes IV, V, and IX are the major virulent Xoo strain types in South China sequentially from the 1990s to the present. Here, we report the isolation of GD0201 and GD0202, which belong to pathotypes IV and IX, respectively, and the complete genome sequence and transcriptomic analysis of GD0201 (IV), GD1358 (V), and GD0202 (IX). We found that resistance genes xa5, Xa23, and Xa27 confer strong resistance to all three Xoo strains, indicating that they are currently good choices for resistance rice breeding. The genome analysis reveals fewer TAL and non-TAL effector coding genes in GD0202 than in the other two strains, potentially contributing to its strong virulence. Transcriptomic analysis of ZH11 inoculated with the three Xoo strains strongly suggests that three Xoo strains for better infection repress the ethylene response factor (ERF) gene family members. Furthermore, weighted gene co-expression network analysis (WGCNA) and protein-protein interaction (PPI) analysis revealed 14 hub genes potentially associated with rice response to the three Xoo strains. The expression of several hub genes was validated to be induced by all three Xoo strains, suggesting its role in bacterial blight disease response to Xoo strains. Genomic analysis of the Xoo strains belonging to pathotypes IV, V, and IX, identification of effectors and genes related to Xoo virulence in rice plants will provide insights into understanding the molecular mechanism underlying rice-Xoo interaction and the gene expression pattern in response to Xoo infection.

Understanding the nature of blast resistance in combined bacterial leaf blight and blast gene pyramided lines of rice variety tellahamsa.

Rice blast and bacterial leaf blight (BLB) are the most limiting factors for rice production in the world which cause yield losses typically ranging from 20 to 30% and can be as high as 50% in some areas of Asia especially India under severe infection conditions. An improved line of Tellahamsa, TH-625-491 having two BLB resistance genes (xa13 and Xa21) and two blast resistance genes (Pi54 and Pi1) with 95% Tellahamsa genome was used in the present study. TH-625-491 was validated for all four target genes and was used for backcrossing with Tellahamsa. Seventeen IBC1F1 plants heterozygous for all four target genes, 19 IBC1F2 plants homozygous for four, three and two gene combinations and 19 IBC1F2:3 plants also homozygous for four, three and two gene combinations were observed. Among seventeen IBC1F1 plants, IBC1F1-62 plant recorded highest recurrent parent genome (97.5%) covering 75 polymorphic markers. Out of the total of 920 IBC1F2 plants screened, 19 homozygous plants were homozygous for four, three and two target genes along with bacterial blight resistance. Background analysis was done in all 19 homozygous IBC1F2 plants possessing BLB resistance (possessing xa13, Xa21, Pi54 and Pi1 in different combinations) with five parental polymorphic SSR markers. IBC1F2-62-515 recovered 98.5% recurrent parent genome. The four, three and two gene pyramided lines of Tellahamsa exhibited varying resistance to blast. Results show that there might be presence of antagonistic effect between bacterial blight and blast resistance genes since the lines with Pi54 and Pi1 combination are showing better resistance than the combinations with both bacterial blight and blast resistance genes.

Genetic Enhancement of Blast and Bacterial Leaf Blight Resistance in Rice Variety CO 51 through Marker-Assisted Selection

The increased use of chemicals in rice farming poses significant issues regarding the emergence of pesticide/fungicide resistance and environmental sustainability concerns. This study was aimed at the genetic improvement of blast, bacterial leaf blight (BB) and gall midge resistance in a popular rice variety CO 51 which already harbours a blast resistance gene Pi54. Efforts were made to pyramid an additional blast resistance gene Pi9 along with two BB resistance genes (xa13 and Xa21) and two gall midge resistance genes (Gm1 and Gm4) into an elite rice variety CO 51 to enhance the resistance level to biotic stresses. The superior lines were selected using functional markers conferring resistance to blast (NBS4 and Pi54MAS linked to Pi9 and Pi54 genes, respectively) and BB [(xa13Prom (xa13) and pTA248 (Xa21)] and SSR markers linked to Gm1 (RM1328) and Gm4 (RM22550) for phenotypic screening and agronomic evaluation. The genotyping and phenotyping of F6 and BC2F6 progenies of CO 51 X 562-4, for agronomic traits and resistance to BB and blast, identified ten superior progenies in F6 and five superior progenies in BC2F6. The breeding lines harbouring both xa13+Xa21 exhibited high levels of resistance to BB (score ≤ 1 cm) and Pi9+Pi54 exhibited strong resistance to blast (score ≤ 2). Identified lines can be evaluated further for varietal improvement or utilised as genetic stocks in breeding programs.

Disease resistance features of the executor R gene Xa7 reveal novel insights into the interaction between rice and Xanthomonas oryzae pv. oryzae.

Bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is a widespread and destructive disease in rice production. Previously, we cloned an executor R gene, Xa7, which confers durable and broad-spectrum resistance to BB. Here, we further confirmed that the transcription activator-like effector (TALE) AvrXa7 in Xoo strains could directly bind to the effector-binding element (EBE) in the promoter of the Xa7 gene. Other executor R genes (Xa7, Xa10, Xa23, and Xa27) driven by the promoter of the Xa7 gene could be activated by AvrXa7 and trigger the hypersensitive response (HR) in tobacco leaves. When the expression of the Xa23 gene was driven by the Xa7 promoter, the transgenic rice plants displayed a similar resistance spectrum as the Xa7 gene, demonstrating that the disease resistance characteristics of executor R genes are mainly determined by their induction patterns. Xa7 gene is induced locally by Xoo in the infected leaves, and its induction not only inhibited the growth of incompatible strains but also enhanced the resistance of rice plants to compatible strains, which overcame the shortcomings of its race-specific resistance. Transcriptome analysis of the Xa7 gene constitutive expression in rice plants displayed that Xa7-mediated disease resistance was related to the biosynthesis of lignin and thus enhanced resistance to Xoo. Overall, our results provided novel insights and important resources for further clarifying the molecular mechanisms of the executor R genes.

Allele Profiling of Bacterial Blight Resistance Genes &lt;em&gt;Xa4, Xa38&lt;/em&gt;, and &lt;em&gt;Xa21&lt;/em&gt; in Selected Sri Lankan Rice Germplasm

In rice, resistance to bacterial blight (BB) is conveyed by several Xa genes, among which Xa4, Xa21 and Xa38 convey durable resistance. Most Sri Lankan rice germplasm is uncharacterized for the alleles carried at Xa genes. Knowledge on the allele profile of major Xa genes of rice accessions/varieties is essential for making informed decisions in rice breeding programs. In the current study, the allele profiles of 42 Sri Lankan rice accessions/varieties were developed targeting three Xa genes (Xa4, Xa21, and Xa38) using intragenic/linked markers amplifying known resistance/susceptible alleles. According to allele profiles, the rice accessions/varieties were grouped into 11 allele-haplotypes. The varieties, Bg 250, Bg 251 and At 354 carried resistance alleles at Xa4, Xa21, and Xa38 (H1 and H3). Most other accessions/varieties reported either one (Xa4- H8 and Xa38- H10) or two resistance alleles (Xa4 and Xa21- H2; Xa4 and Xa38- H9; Xa21 and Xa38- H11). Three allele-haplotypes were reported with a novel allele at Xa4 (H4, H5, and H6). Ma wee and Kuru wee reported susceptible alleles at all three Xa genes (H7). A significant association (p≤0.05) between the Xa allele-haplotypes and the BB disease response was not observed. To achieve durable BB disease resistance in rice, it is recommended to introgress resistance alleles of the major Xa genes when releasing rice varieties, for which the reported allele profile of Xa4, Xa21 and Xa38 genes in the selected panel of Sri Lankan rice varieties/accessions will be of great importance.

Comparison of Blast, Bacterial Leaf Blight and Brown Plant Hopper Introgressed Lines for Yield and Morphological Traits Over Original Line

Rice as a staple food for very large population suffers from various biotic and abiotic stresses. Among the biotic stresses, Blast, Bacterial leaf blight and Brown plant hopper (BPH) are considered to most potential threats that significantly affect the rice productivity. The use of chemical usage for controlling these diseases and pest attacks is not environmentally friendly and is expensive. Using Molecular Marker assisted backcross breeding program we have improved one of our hybrid parental line with 5 genes (xa13, Xa21, Pi54, Bph20 and Bph21). We have developed 15 near isogenic lines having similar agronomical characters as of recipient parent, they are promising for their direct induction in breeding program. Our results indicated that out of fifteen lines, Six lines i.e. GK 101-12, GK 101-15, GK 101-9, GK 101-5 and GK 101-2 out-performed in all the three locations tested, they had not only have very high level of resistance to BLB, Blast and BPH but also showed significantly higher yield compared to susceptible check as well as recipient parent. These lines may be used for improvement of our existing hybrid and also for developing of new hybrids with other CMS lines. These lines are also useful for developing new set of restorer lines through (R x R) and also useful for introgression of wide spectrum of resistance to the varieties/hybrid.

The Effect of Tapak Liman (Elephantopus scaber L.) Extract on Xa4 Gene Expression in Rice IR64 Infected by Bacterial Leaf Blight (Xanthomonas oryzae)

Bacterial leaf blight, caused by Xanthomonas oryzae pv. oryzae (Xoo), represents a significant threat to rice (Oryza sativa) production. Induce plant resistance has emerged as a promising control strategy. The extract of Tapak Liman (Elephantopus scaber) has been considered a promising agent due to its antimicrobial properties, with several of its compounds showing its potential as inducers of plant resistance. This study aimed at elucidating the impact of Tapak Liman extract on the expression of resistance Xa4 gene in rice that plays a crucial role in the synthesis mechanism leading to cell wall thickening. To explore this effect, we analyzed Xa4 gene expression using the reverse transcription-polymerase chain reaction (RT-PCR) technique, followed by a semi-quantitative descriptive analysis. Our results demonstrate that the application of Tapak Liman extracts at a concentration of 10 mg/ml significantly upregulates Xa4 gene expression in the IR64 compared with other concentrations, 1 mg/ml or 5 mg/ml. Furthermore, the observed higher expression of the Xa4 gene persists until 5 days after pathogen inoculation, which is also implicated with a less developed lesion on rice leaves by 76% compared with the control.

Introgression of bacterial leaf blight (BLB) resistant gene, Xa7 into MARDI elite variety, MR219 by marker assisted backcrossing (MABC) approach.

Bacterial leaf blight (BLB) is one of the major rice diseases in Malaysia. This disease causes substantial yield loss as high as 70%. Development of rice varieties which inherited BLB resistant traits is a crucial approach to promote and sustain rice industry in Malaysia. Hence, this study aims were to enhance BLB disease resistant characters of high yielding commercial variety MR219 through backcross breeding approach with supporting tool of marker-assisted selection (MAS). Broad spectrum BLB resistance gene, Xa7 from donor parent IRBB7 were introgressed into the susceptible MR219 (recurrent parent) using two flanking markers ID7 and ID15. At BC3F4, we managed to generate 19 introgressed lines with homozygous Xa7 gene and showed resistant characteristics as donor parent when it was challenged with Xanthomonas oryzae pv. oryzae through artificial inoculation. Recurrent parent MR219 and control variety, MR263 were found to be severely infected by the disease. The improved lines exhibited similar morphological and yield performance characters as to the elite variety, MR219. Two lines, PB-2-107 and PB-2-34 were chosen to be potential lines because of their outstanding performances compared to parent, MR219. This study demonstrates a success story of MAS application in development of improved disease resistance lines of rice against BLB disease.

Genome Resource for the Highly Virulent Xanthomonas oryzae pv. oryzae Strain HN2011 from China

Xanthomonas oryzae pv. oryzae ( Xoo) is the causal bacterium of rice bacterial blight (BB), which is one of the most destructive bacterial diseases of rice worldwide. Although more than 40 BB resistance genes ( Xa genes) have been identified, only a few conferring broad resistance (e.g., Xa4 and Xa21) have been widely used for rice breeding in Asia. The narrow genetic basis for the BB resistance of rice cultivars has resulted in the emergence of new pathogenic strains that can overcome the resistance of commonly grown rice cultivars derived from breeding programs. For example, Xoo strain HN2011, which was isolated in Hainan (China), can overcome the resistance mediated by multiple BB resistance genes, including Xa4 and Xa21. We herein present the complete genome sequence of HN2011 generated by Nanopore sequencing. The genomic data will be useful for elucidating the genomic variations of Xoo and will contribute to clarifying the interaction between Xoo and rice. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Genetic Enhancement for Biotic Stress Resistance in Basmati Rice through Marker-Assisted Backcross Breeding.

Pusa Basmati 1509 (PB1509) is one of the major foreign-exchange-earning varieties of Basmati rice; it is semi-dwarf and early maturing with exceptional cooking quality and strong aroma. However, it is highly susceptible to various biotic stresses including bacterial blight and blast. Therefore, bacterial blight resistance genes, namely, xa13 + Xa21 and Xa38, and fungal blast resistance genes Pi9 + Pib and Pita were incorporated into the genetic background of recurrent parent (RP) PB1509 using donor parents, namely, Pusa Basmati 1718 (PB1718), Pusa 1927 (P1927), Pusa 1929 (P1929) and Tetep, respectively. Foreground selection was carried out with respective gene-linked markers, stringent phenotypic selection for recurrent parent phenotype, early generation background selection with Simple sequence repeat (SSR) markers, and background analysis at advanced generations with Rice Pan Genome Array comprising 80K SNPs. This has led to the development of Near isogenic lines (NILs), namely, Pusa 3037, Pusa 3054, Pusa 3060 and Pusa 3066 carrying genes xa13 + Xa21, Xa38, Pi9 + Pib and Pita with genomic similarity of 98.25%, 98.92%, 97.38% and 97.69%, respectively, as compared to the RP. Based on GGE-biplot analysis, Pusa 3037-1-44-3-164-20-249-2 carrying xa13 + Xa21, Pusa 3054-2-47-7-166-24-261-3 carrying Xa38, Pusa 3060-3-55-17-157-4-124-1 carrying Pi9 + Pib, and Pusa 3066-4-56-20-159-8-174-1 carrying Pita were identified to be relatively stable and better-performing individuals in the tested environments. Intercrossing between the best BC3F1s has led to the generation of Pusa 3122 (xa13 + Xa21 + Xa38), Pusa 3124 (Xa38 + Pi9 + Pib) and Pusa 3123 (Pi9 + Pib + Pita) with agronomy, grain and cooking quality parameters at par with PB1509. Cultivation of such improved varieties will help farmers reduce the cost of cultivation with decreased pesticide use and improve productivity with ensured safety to consumers.

Establishment of Functional PCR-Based Markers against Bacterial Leaf Blight Disease in Rice Landraces of Yunnan Province of China.

Bacterial leaf blight is a devastating disease of rice worldwide. The resistant genes are routinely transferred from landraces to cultivated varieties through backcross breeding along with marker-assisted selection. In the present study, we use the gene-specific markers to screen the rice landraces in Yunnan Province of China. We collected 404 representative samples of 24 different rice landraces from Yunnan Province of China. The initial PCR-based screening suggested that the leaf blight resistance was not evenly distributed in Yunnan Province. Our results indicate that there is a complete loss of resistance for landraces based on xa5 and xa13 genes. On the other hand, landraces harboring Xa7 and Xa21 showed a high level of resistance. Using gene-specific PCR-based data, we were able to identify the resistant, susceptible and heterozygous populations across Yunnan Province. The widely used Xa21 gene alone showed a remarkable level of resistance throughout the province, indicating its potential to develop broad-spectrum resistance in rice germplasm. The key aspects of bacterial blight spread according to local sites in Yunnan Province and the resistance conferred by different landraces due to the presence of different resistance genes are discussed.

Marker-assisted enhancement of bacterial blight (Xanthomonas oryzae pv. oryzae) resistance in a salt-tolerant rice variety for sustaining rice production of tropical islands.

Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae is a major disease of rice, specially in the tropical regions of the world. Developing rice varieties with host resistance against the disease is the most effective and economical solution for managing the disease. Pyramiding resistance genes (Xa4, xa5, xa13,and Xa21) in popular rice varieties using marker-assisted backcross breeding (MABB) has been demonstrated as a cost-effective and sustainable approach for establishing durable BB resistance. Here, we report our successful efforts in introgressing four resistance genes (Xa4, xa5, xa13, and Xa21) from IRBB60 to CARI Dhan 5, a popular salt-tolerant variety developed from a somaclonal variant of Pokkali rice, through functional MABB. Both BB and coastal salinity are among the major challenges for rice production in tropical island and coastal ecosystems. Plants with four, three, and two gene pyramids were generated, which displayed high levels of resistance to the BB pathogen at the BC3F2 stage. Under controlled salinity microplot environments, the line 131-2-175-1223 identified with the presence of three gene pyramid (Xa21+xa13+xa5) displayed notable resistance across locations and years as well as exhibited a salinity tolerance comparable to the recurrent parent, CARI Dhan 5. Among two BB gene combinations (Xa21+xa13), two lines, 17-1-69-334 and 46-3-95-659, demonstrated resistance across locations and years, as well as salt tolerance and grain production comparable to CARI Dhan 5. Besides salinity tolerance, five lines, 17-1-69-179, 46-3-95-655, 131-2-190-1197, 131-2-175-1209, and 131-2-175-1239, exhibited complete resistance to BB disease. Following multilocation testing, potential lines have been identified that can serve as a prospective candidate for producing varieties for the tropical Andaman and Nicobar Islands and other coastal locations, which are prone to BB and coastal salinity stresses.

Pyramiding resistance genes for bacterial leaf blight (Xanthomonas oryzae pv. Oryzae) into the popular rice variety, Pratikshya through marker assisted backcrossing.

Bacterial leaf blight (BLB) is one of the major biotic stress in rice cultivation. Management techniques, such as the development of BLB-resistant cultivars, are required to lessen the severity of the disease attack and yield losses. Pratikshya was selected in the present investigation as the recipient parent, as it is one of the popular high-yielding rice varieties of Odisha, India, which is having excellent grain as well as cooking quality. However, Pratikshya is highly susceptible to BLB which is prevalent in Eastern Indian region. Three major BLB resistance genes xa5, xa13, and Xa21 from the donor source Swarna MAS (CR Dhan 800) were attempted to introduce into Pratikshya through a marker-assisted backcross breeding program. Those markers closely linked to the target genes were employed for foreground selection in the segregating generations till BC2F3. In each backcross generation, progenies containing all three targeted resistance genes and phenotypically more similar to the recipient parent, Pratikshya were selected and backcrossed. Screening of 1,598 plants of the BC2F2 population was conducted against BLB using Xoo inoculum and 35 resistant plants similar to Pratikshya were carried forward to the next generation. In the BC2F3 generation, 31 plants were found to possess all the three resistance genes. For background selection of plants carrying resistance genes 45 polymorphic SSR markers were employed. Evaluation of the pyramided lines at BC2F4 generation exhibited that, most pyramided lines were similar to Pratikshya in terms of morphological features and yield parameters, and some lines were superior to the recurrent parent in terms of morphological features and yield parameters. The three-gene pyramided lines showed a high level of resistance to BLB infection and are anticipated to offer a significant yield advantage over the recipient parent Pratikshya.The pyramided lines can further be used for multi-location trial, so as to be released as a variety or can be used as a potential donor for BLB resistance genes.

Molecular and Morphological Characterization of Introgression Lines with Resistance to Bacterial Leaf Blight and Blast in Rice.

The present study evaluates marker assisted forward breeding (MAFB)-derived disease resistant introgression lines (ILs) which do not have the targeted resistance genes for bacterial blight (xa5 + xa13 + Xa21) and blast (Pi2 + Pi9 + Pi54). The ILs were derived in the background of two elite rice cultivars, Krishna Hamsa [Recurrent Parent 1 (RP1)] and WGL 14 (RP2), involving multi-parent inter-crossing. Molecular characterization with gene specific markers for seven reported resistance genes each for bacterial blight (Xa33, Xa38, xa23, Xa4, xa8, Xa27 and Xa41) and blast (Pi1, Pi20, Pi38, Pib, Pitp, Pizt and Pi40) revealed the presence of xa8 and Xa38, in addition to the targeted xa5, xa13 and Xa21 for bacterial blight resistance and Pi1, Pi38, Pi40, Pi20, Pib and Pipt, in addition to the targeted Pi9 and Pi54, for blast resistance in various combinations. A maximum of nine resistance genes xa5 + Xa21 + Pi54 + xa8 + Pipt + Pi38 + Pi1 + Pi20 + Pib was observed in RP1-IL 19030 followed by eight genes xa5 + xa13 + Xa21 + xa8 + Pi9 + Pipt + Pi1 + Pi20 in two RP2-ILs, 19344 and 19347. ANOVA revealed the presence of significant variability for all the yield traits except "days to 50% flowering" (DFF). Box plots depicted the seasonal differences in the phenotypic expression of the yield traits. There was significant positive association of grain yield with days to flowering, tiller number and panicle number. Thousand grain weight is also significantly and positively correlated with grain yield. On the contrary, grain yield showed a significantly negative association with plant height. Multi-parent selective inter-crossing in the present study not only led to the development of high yielding disease resistant ILs but also enhanced recovery of the recurrent parent via selection for essential morphological features. More than 90.0% genetic similarity in the ILs based on SNP-based background selection demonstrated the success of multi-parent selective intercrossing in the development of disease resistant NILs.