Resistant Rice Lines Research Articles

The pathogenicity-associated regulators participating in the regulatory cascade for RaxSTAB and RaxX in Xanthomonas oryzae pv. oryzae.

The RaxX sulfopeptide, secreted via a type Ι secretion system, is crucial for activating XA21-mediated innate immunity in resistant rice lines bearing the XA21 receptor kinase. Certain pathogenicity-associated regulators that control the expression of the raxSTAB-raxX gene cluster have been functionally characterized, but the comprehensive regulatory cascade of RaxSTAB and RaxX in Xanthomonas oryzae pv. oryzae (Xoo) remains incompletely understood. Our investigation revealed that pathogenicity-associated regulators, including HrpG, HrpX, VemR, PhoR, and Clp, form a regulatory cascade governing the expression of the raxSTAB-raxX gene cluster. HrpG regulates the raxSTAB-raxX gene cluster transcription through the key regulator HrpX. VemR also participates in the transcription of the raxSTAB-raxX. The histidine kinase PhoR positively modulates raxSTAB-raxX expression, while the global regulator Clp directly binds the raxX promoter region to promote its transcription. These findings shed light on the intricate regulatory cascade of rax-related genes in Xoo, emphasizing the complex roles of pathogenicity-associated regulators within the pathogenic regulatory system.

Multiomics-assisted characterization of rice-Yellow Stem Borer interaction provides genomic and mechanistic insights into stem borer resistance in rice.

By deploying a multi-omics approach, we unraveled the mechanisms that might help rice to combat Yellow Stem Borer infestation, thus providing insights and scope for developing YSB resistant rice varieties. Yellow Stem Borer (YSB), Scirpophaga incertulas (Walker) (Lepidoptera: Crambidae), is a major pest of rice, that can lead to 20-60% loss in rice production. Effective management of YSB infestation is challenged by the non-availability of adequate sources of resistance and poor understanding of resistance mechanisms, thus necessitating studies for generating resources to breed YSB resistant rice and to understand rice-YSB interaction. In this study, by using bulk-segregant analysis in combination with next-generation sequencing, Quantitative Trait Loci (QTL) intervals in five rice chromosomes were mapped that could be associated with YSB resistance at the vegetative phase in a resistant rice line named SM92. Further, multiple SNP markers that showed significant association with YSB resistance in rice chromosomes 1, 5, 10, and 12 were developed. RNA-sequencing of the susceptible and resistant lines revealedseveral genes present in the candidate QTL intervals to be differentially regulated upon YSB infestation. Comparative transcriptome analysis revealed a putative candidate gene that was predicted to encode an alpha-amylase inhibitor. Analysis of the transcriptome and metabolite profiles further revealed a possible link between phenylpropanoid metabolism and YSB resistance. Taken together, our study provides deeper insights into rice-YSB interaction and enhances the understanding of YSB resistance mechanism. Importantly, a promising breeding line and markers for YSB resistance have been developed that can potentially aid in marker-assisted breeding of YSB resistance among elite rice cultivars.

Genotype-by-environment interaction effects on blast disease severity and genetic diversity of advanced blast-resistant rice lines based on quantitative traits

IntroductionAmong the rice diseases, rice blast caused by the pathogen Magnaporthe oryzae is a major threat to the global rice cultivation. This experiment was aimed at investigating the genotype by environment interaction effects on the severity of blast disease and variability of the advanced blast resistant rice lines using quantitative characters.Materials and methodsThe experiment was laid out in randomized complete block design conducted at three locations. Data were collected on 21 traits which included vegetative, physiological, yield and yield components and were subjected to analysis of variance and variance component analysis. Cluster analysis was authenticated using principal component analysis for genotypes’ classification.Results and discussionAll vegetative and yield traits showed highly significant variation among the advanced lines and the check. Seberang Prai showed the highest average yield (5.62t/ha), followed by Tanjung Karang (5.39t/ha) and UPM (4.97t/ha). All the advanced lines showed high resistance to blast disease. Evaluation across the three environments indicated that genotype G3, from MR219 based population, had the highest yield and resistance to blast infection. Genotype G21, from MR263 based population, performed best across the three environments studied and were selected for further breeding programme. The two selected lines, three and four clusters derived from MR219 and MR263 based populations, respectively, were recommended as new lines for further breeding programmes.

Toxicity and selective mechanism of imazamox by weedy rice and imidazolinone‐resistant rice in China

AbstractWeedy rice (Oryza spp.) is a notorious weed in direct‐seeding paddy fields. Because it has anatomical and physiological traits similar to those of cultivated rice, no selective herbicide is effective in controlling weedy rice growing among conventional rice cultivars. Imidazolinone (IMI)‐resistant rice lines JD372 and JJ818 have been planted with imazamox to control weedy rice in Jiangsu and Shanghai, China. Whole‐plant dose–response analysis showed that imazamox exhibited high efficacy against three populations of weedy rice. The ED90 of weedy rice populations FN‐5, GY‐8, and HY‐3 were 46.87, 61.43, and 52.17 g a.i. ha−1, respectively, close to the recommended field dose (50 g a.i. ha−1) of imazamox. Conversely, the ED10 values of JD372 and JJ818 were slightly lower than 50 g a.i. ha−1. These findings indicate that imazamox can control weedy rice production in JD372 and JJ818 fields. The acetolactate synthase (ALS) sensitivity of JD372 in vitro was 1714.89‐fold lower to imazamox than was that of FN‐5. ALS gene sequencing revealed a Ser653Asn point mutation—a common mutation that confers resistance to IMI herbicides in JD372. In addition, higher ALS expression levels in JD372 were found at 24 and 72 h after imazamox treatment. ALS overexpression might partially compensate for the ALS activity of JD372 that was suppressed by imazamox.

Performance of tungro disease resistant rice lines in Lanrang, South Sulawesi, Indonesia

Efforts to increase rice production and productivity nationally are still being disturbed by plant pest organisms. One of the diseases that have received serious attention is the tungro disease, which has the ability to attack rice plants in endemic areas. The purpose of this study was to investigate the resistance of several rice lines towards the Lanrang South Sulawesi tungro virus inoculum including morphological characteristics. This study was conducted at the Tungro Disease Research station from June to September 2020. A total of 14 lines were tested for resistance compared to the Tukad Petanu, Tukad Balian, Inpari 8 and Tukad Unda lines against the tungro disease. The rice lines were planted in the form of an augmented design consisting of five blocks. Each block contained three test lines and four comparison varieties, the lines were planted in plots (1 × 5) m, with 25 × 25 cm spacings. The results showed that the population of green leafhoppers at the age of 20 DAP and 30 DAP was found to range from 1 to 95 individuals per line/variety, while the incidence of tungro disease was 1.3 to 11.3% in the three test lines, namely STLRG17 15 LR 1, STLRG17 15 LR 2, and STLRG17 108 LR 1. The highest 1000 seed weight was found in the STLRG17 176 LR 2 line (25.1 g) and the lowest was STLRG17 51 LR 1 (17.6 g). The STLRG17 175 LR 1, STLRG17 176 LR, STLRG17 -175-LR-1, STLRG17-28-LR-1, and STLRG17-26-LR-2 5 lines had a fairly good and consistent appearance at 1000 seed weight, higher yield, productive tillers, plant height, and resistance to tungro disease compared to the comparison varieties.

Molecular characterization and screening of Xanthomonas oryzae pv. oryzae, isolated from Pakistan for prediction of bacterial leaf blight-resistant basmati rice

Bacterial leaf blight (BLB) is a devastating disease of rice caused by Xanthomonas oryzae pv.oryzae (Xoo), severely affects grain quality and reduces yield in all rice-growing areas of Pakistan. The pathogen is highly dynamic and quickly evolves itself when encountered with new resistant genes, hence, the knowledge about existing virulence range within the pathogen population and availability of corresponding resistance gene source is of immense importance. The present study focused on molecular dissection and evaluating the effectiveness of different resistance gene combinations against Xoo isolates collected from seven major rice-growing districts of Punjab Pakistan. Phenotypic characterization of collected Xoo isolates has shown that all of them were rod-shaped Gram-negative bacteria. However, oryzae species and oryzae pathovar were confirmed in only 22 out of 50 isolates using multiplex PCR. Analysis of loop-mediated isothermal amplification validated the lineage and close relatedness of Pakistani Xoo isolates with the already reported Asian Xoo population. Pathogenicity test on susceptible rice variety Super Basmati has shown that out of twenty-two tested Xoo isolates, four isolates from three different districts fell into the most virulent category with an average lesion length of ≥15 cm. Pathotyping of selected resistant rice lines against Xoo isolates distributed 22 isolates into nine pathotypes based on their interaction with R genes. Current molecular and phenotypic profiling of isolated Pakistani Xoo isolates may serve as a valuable reference for global comparison to manage BLB disease of rice in real-time.

Diversity of Xanthomonas oryzae pv. Oryzae on susceptible and resistant rice lines in bacterial blight hot spot areas of the Philippines

Diversity of Xanthomonas oryzae pv. Oryzae on susceptible and resistant rice lines in bacterial blight hot spot areas of the Philippines

Seeds Phenotypes Characterization of Promising Tungro-Resistant Rice Lines

Breeding activities to produce a new site-specific rice varieties resistant to tungro require of suitable genetic materials as cross-breeding materials. This research aims to determine the seed phenotypic characters of promising tungro resistant rice lines and their similarity. The research was conducted using a completely randomized design with treatment of 42 promising tungro-resistant rice lines, 1 resistant rice variety (Inpari 7) and 1 susceptible rice variety (TN1), that each of which was repeated 3 times. The characters were observed included of quantitative and qualitative characters. Observation of seed characters was carried out based on the standard system of characterization and evaluation of rice plants. The similarity of seed characters was analyzed by using the NTSYS pc version 2.1 program and displayed in the form of a dendrogram. The results showed that most of the tested lines had the same quantitative characters as the Inpari 7 variety. The value of variability of diversity was included in the broad category of >4, with the lowest similarity coefficient of 63% and the highest of 94%. The similarity analysis based on the seed characters resulted in 2 large groups consisting of 41 lines belonging to the Inpari 7 group and 1 line belonging to the TN1 group. The lines that were incorporated in the Inpari 7 group were further divided into two subgroups of 39 and 2 lines, respectively. The results of this research are preliminary data to obtain an information of the relationship between seed characters and tungro resistance properties.

Mutation in BEIIb mitigates the negative effect of the mutation in ISA1 on grain filling and amyloplast formation in rice.

Mutation of the BEIIb gene in an isa1 mutant background mitigates the negative effect of the ISA1 mutation on grain filling, and facilitates recovery of amyloplast formation in rice endosperm. In this study, the effect of branching enzyme IIb and isoamylase 1 deficiency on starch properties was demonstrated using high resistant starch rice lines, Chikushi-kona 85 and EM129. Both lines harbored a mutation in the BEIIb and ISA1 genes and showed no BEIIb and ISA1 activity, implying that both lines are beIIb isa1 double mutants. The amylopectin long chain and apparent amylose content of both mutant lines were higher than those of the wild-type. While both mutants contained loosely packed, round starch grains, a trait specific to beIIb mutants, they also showed collapsed starch grains at the center of the endosperm, a property specific to isa1 mutants. Furthermore, beIIb isa1 double mutant F2 lines derived from a cross between Chikushi-kona 85 and Nishihomare (wild-type cultivar) showed significantly heavier seed weight than the beIIb and isa1 single mutant lines. These results suggest that co-occurrence of beIIb and isa1 mutant alleles in a single genetic background mitigates the negative effect of the isa1 allele on grain filling, and contributes to recovery of the amyloplast formation defect in the isa1 single mutant.

Observation of promising tungro resistant rice lines in West Sulawesi

Food needs, especially rice, are a priority for agricultural businesses in Indonesia. The development of the world population in general and Indonesia in particular encourages a rapid increase in rice productivity. So it is demanded to have variety of rice that is resistant to disease and has superior rice productivity. Efforts to increase rice yields can not be separated from the efforts of assembling new superior varieties that are disease resistant as well as high yield potential. One of the plant breeding activities is observation activities. To explore the potential of rice strains after the screening stage, it is necessary to evaluate the germplasm or selected rice strains so that genotype can be screened which gives a positive response to both biotic and abiotic stresses. Tungro disease is generally the main problem in efforts to increase rice productivity. Tungro disease can attack rice plants from seedlings, vegetative stadia leaves through the host of green aphrodisiacs (Nephotetix vieressens). In vulnerable rice and supportive environmental conditions, this disease can cause farmers to fail to harvest or ‘puso’. The use of resistant varieties is the most practical and economical ways of controlling tungro disease. The purpose of the study was to evaluate the resistance of the rice breeddings lines to tungro disease. The research was conducted during Planting Period II in 2019 in the endemic area of Tungro Kalukku, West Sulawesi. The genetic materials tested as many as 26 strains from the group of researcher germplasm of Tungro research station and resistant check varieties namely Inpari 36 and comparison production namely Ciherang. The results showed that the strains tested had a diversity of different resistances that showed varying responses to tungro disease. Rice breeddings the best from checker varieties Ciherang and Inpari 36 namely: Strains No.2, 10, 12, 16, and 19 can be recommended for used further testing.

Genome-wide association study and transcriptome analysis discover new genes for bacterial leaf blight resistance in rice (Oryza sativa L.)

BackgroundRice (Oryza sativa) bacterial leaf blight (BLB), caused by the hemibiotrophic Xanthomonas oryzae pv. oryzae (Xoo), is one of the most devastating diseases affecting the production of rice worldwide. The development and use of resistant rice varieties or genes is currently the most effective strategy to control BLB.ResultsHere, we used 259 rice accessions, which are genotyped with 2 888 332 high-confidence single nucleotide polymorphisms (SNPs). Combining resistance variation data of 259 rice lines for two Xoo races observed in 2 years, we conducted a genome-wide association study (GWAS) to identify quantitative trait loci (QTL) conferring plant resistance against BLB. The expression levels of genes, which contains in GWAS results were also identified between the resistant and susceptible rice lines by transcriptome analysis at four time points after pathogen inoculation. From that 109 candidate resistance genes showing significant differential expression between resistant and susceptible rice lines were uncovered. Furthermore, the haplotype block structure analysis predicted 58 candidate genes for BLB resistance based on Chr. 7_707158 with a minimum P-value (–log 10 P = 9.72). Among them, two NLR protein-encoding genes, LOC_Os07g02560 and LOC_Os07g02570, exhibited significantly high expression in the resistant line, but had low expression in the susceptible line of rice.ConclusionsTogether, our results reveal novel BLB resistance gene resources, and provide important genetic basis for BLB resistance breeding of rice crops.

Mixture interactions of quizalofop and reduced rates of halosulfuron

AbstractA field study was conducted in 2017 and 2018 at the Louisiana State University Agricultural Center H. Rouse Caffey Rice Research Station near Crowley, LA, to evaluate the impact of reduced rates of halosulfuron on quizalofop activity in Louisiana rice production. Halosulfuron and a prepackaged mixture of halosulfuron plus thifensulfuron were evaluated at 0, 17, 35, or 53 g ai ha−1 and 34 or 53 g ai ha−1, respectively, in a mixture with quizalofop at 120 g ai ha−1. Control of barnyardgrass, red rice, and two non-acetyl-CoA carboxylase resistant rice lines, CL-111 and CLXL-745, were recorded at 14 and 28 d after treatment (DAT). The red rice, CL-111, and CLXL-745 represented a weedy rice population. Across all species evaluated at 14 DAT, all mixtures containing halosulfuron and halosulfuron plus thifensulfuron resulted in antagonism with an observed control of 79% to 90%, compared with an expected control of 96% to 99%. At 28 DAT, all mixtures containing halosulfuron resulted in neutral interactions for barnyardgrass control. Quizalofop mixed with halosulfuron plus thifensulfuron at the lower rate of 34 g ha−1 was able to overcome the antagonism compared with the higher rate of 53 g ha−1 for barnyardgrass control at 28 DAT. Both the high and the low rate of halosulfuron plus thifensulfuron resulted in antagonistic interaction for red rice, CL-111, and CLXL-745 control at 28 DAT. This research suggests that mixing quizalofop with halosulfuron plus thifensulfuron should be avoided, especially at the higher rate of 53 g ha−1.

Correlation of phenotype components with yield of promising tungro resistant superior rice lines

The assembly of new high-yield and disease-resistant rice varieties is one of the efforts to increase the rice production and productivity in Indonesia. New site-specific varieties that match farmer preferences are targeted for plant breeding. The yield test is one of the activities in plant breeding to identify any promising lines that have adaptability to a specific growing environment. The purpose of this study was to determine the correlation of the phenotypic components with the yield of the promising superior rice lines which have high yield potential and are resistant to tungro disease. The research was conducted in the tungro endemic area of Lanrang South Sulawesi during the rainy season (MH) December 2017 to March 2018. A total of 20 rice slaves were arranged in an augmented design consisting of 4 blocks, each block there were 5 test lines and 2 comparison varieties namely Ciherang and Inpari 7 Lanrang. The components observed included plant height, flowering age, number of panicles, number of filled grains per panicle, number of empty grains per panicle, 1000 grain weight, yield weight per hectare, clump shape and level of lodging. The results showed that the yields of 10 lines were higher than one or both comparators, namely BP11224F, BP12280-4F-7, BP57964F, BP11206F, BP12280-4F-4, BP12280-3F-16, BP12280-3F-2, BP122803F5, BP11208F-7, and BP12280-3f-13. The value of R = 0.557, which means that there is a strong correlation between the components of growth and the level of yield. The value of R square = 0.310 indicates that the ability of the six growth components were observed affects the rice yield by 31% and there are still 69% other components that affect the yield.

Identification of Bacterial Blight Resistance Loci in Rice (Oryza sativa L.) against Diverse Xoo Thai Strains by Genome-Wide Association Study

Bacterial leaf blight (BLB) is a serious disease affecting global rice agriculture caused by Xanthomonas oryzae pv. oryzae (Xoo). Most resistant rice lines are dependent on single genes that are vulnerable to resistance breakdown caused by pathogen mutation. Here we describe a genome-wide association study of 222 predominantly Thai rice accessions assayed by phenotypic screening against 20 Xoo isolates. Loci corresponding to BLB resistance were detected using >142,000 SNPs. We identified 147 genes according to employed significance thresholds across chromosomes 1–6, 8, 9 and 11. Moreover, 127 of identified genes are located on chromosomal regions outside estimated Linkage Disequilibrium influences of known resistance genes, potentially indicating novel BLB resistance markers. However, significantly associated SNPs only occurred across a maximum of six Xoo isolates indicating that the development of broad-spectrum Xoo strain varieties may prove challenging. Analyses indicated a range of gene functions likely underpinning BLB resistance. In accordance with previous studies of accession panels focusing on indica varieties, our germplasm displays large numbers of SNPs associated with resistance. Despite encouraging data suggesting that many loci contribute to resistance, our findings corroborate previous inferences that multi-strain resistant varieties may not be easily realised in breeding programs without resorting to multi-locus strategies.

Options for tackling pathogen resistance by genome editing in rice

Abstract Rice is the most important staple crop in the developing world and its productivity is critical for food security, development, and poverty elimination. Worldwide, approximately 900 million people from low-income households depend on rice. Ninety percent of the global rice is produced in Asia, mainly by small-scale producers who farm 0.4 ha or less. Productivity is increasingly threatened by biotic stresses from viruses, bacteria, fungi, nematodes, insects, and arachnids. Nowadays, genome editing provides unique opportunities to generate variants of elite lines that are resistant to one or multiple diseases. We provide examples in which the simplest form of genome editing is used to block pathogens from exploiting host susceptibilities, thereby creating a robust broad-spectrum resistance. We highlight the editing of promoter sequences of rice SWEET sugar transporters, which led to resistance against Bacterial leaf blight (BLB) as a blueprint for the use of new breeding technologies in fighting other important crop diseases and for stacking with other useful traits. Notably, successful strategies for protecting against pathogen infections require more than just resistant rice lines, but also better maintenance and strategies to improve the living standards of small-scale producers.

Proteome-Wide Analyses Provide New Insights into the Compatible Interaction of Rice with the Root-Knot Nematode Meloidogyne graminicola.

The root-knot nematode Meloidogyne graminicola is an important pathogen in rice, causing huge yield losses annually worldwide. Details of the interaction between rice and M. graminicola and the resistance genes in rice still remain unclear. In this study, proteome-wide analyses of the compatible interaction of the japonica rice cultivar “Nipponbare” (NPB) with M. graminicola were performed. In total, 6072 proteins were identified in NPB roots with and without infection of M. graminicola by label-free quantitative mass spectrometry. Of these, 513 specifically or significantly differentially expressed proteins were identified to be uniquely caused by nematode infection. Among these unique proteins, 99 proteins were enriched on seven Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. By comparison of protein expression and gene transcription, LOC_Os01g06600 (ACX, a glutaryl-CoA dehydrogenase), LOC_Os09g23560 (CAD, a cinnamyl-alcohol dehydrogenase), LOC_Os03g39850 (GST, a glutathione S-transferase) and LOC_Os11g11960 (RPM1, a disease resistance protein) on the alpha-linolenic acid metabolism, phenylpropanoid biosynthesis, glutathione metabolism and plant–pathogen interaction pathways, respectively, were all associated with disease defense and identified to be significantly down-regulated in the compatible interaction of NPB with nematodes, while the corresponding genes were remarkably up-regulated in the roots of a resistant rice accession “Khao Pahk Maw” with infection of nematodes. These four genes likely played important roles in the compatible interaction of rice with M. graminicola. Conversely, these disease defense-related genes were hypothesized to be likely involved in the resistance of resistant rice lines to this nematode. The proteome-wide analyses provided many new insights into the interaction of rice with M. graminicola.

SWATH-MS-based quantitative proteomics reveals a uniquely intricate defense response in Cnaphalocrocis medinalis-resistant rice

Cnaphalocrocis medinalis is a major insect pest of rice in Asia. A few defensive enzymes were reported to show higher activities in a resistant rice line (Qingliu) than in a susceptible rice line (TN1) upon leaffolder infestation. However, the overall molecular regulation of the rice defense response against leaffolder herbivory is unknown. Here, differential proteomic analysis by SWATH-MS was performed to identify differentially expressed proteins between the two rice varieties, Qingliu and TN1, at four time points of leaffolder herbivory, 0, 6, 24, and 72 h. Gene Ontology (GO) enrichment of the differentially expressed proteins indicated overrepresentation of (1) photosynthesis, (2) amino acid and derivative metabolic process, and (3) secondary metabolic process. Phenylalanine ammonia lyase and chalcone synthase, which catalyze flavonoid biosynthesis, and lipoxygenase, which catalyzes jasmonic acid biosynthesis, exhibited higher expression in Qingliu than in TN1 even before insect herbivory. Momentary activation of the light reaction and Calvin cycle was detected in Qingliu at 6 h and 24 h of insect herbivory, respectively. At 72 h of insect herbivory, amino acid biosynthesis and glutathione-mediated antioxidation were activated in Qingliu. A defense response involving jasmonic acid signaling, carbon remobilization, and the production of flavonoids and glutathione could underlie the resistance of Qingliu to leaffolder.

Assessment of Agro-Morphologic Performance, Genetic Parameters and Clustering Pattern of Newly Developed Blast Resistant Rice Lines Tested in Four Environments

Multi-environmental yield trial is very vital in assessing newly developed rice lines for its adaptability and stability across environments especially prior to release of the newly developed variety for commercial cultivation. The growth performance and phenotypic variability of these genotypes are the combination of environment, genotype and genotype by environment (G×E) interaction factors. Thus, evaluation creates an opportunity for effective selection of superior genotypes. The objectives of this study were to evaluate the newly developed blast resistant rice lines in varied environmental conditions, precisely measure the response of the advanced lines in multiple environments and classify the genotypes into groups that could serve as varieties for commercial cultivation. Genetic materials included 18 improved blast resistant rice lines and the recipient parent MR219. The total of 19 newly developed genotypes was evaluated under four varied environments in Peninsular Malaysia. The experiments were carried out using randomized complete block design (RCBD) with three replications at each environment. Data were collected on the vegetative, yield and yield component traits. Descriptive statistics (mean performance) and analysis of variance were conducted using SAS Software version 9.4. Genotypic and phenotypic coefficients, phenotypic variance component, heritability and genetic advance were also determined. Analysis of variance revealed that all traits were significantly different for genotypes except days to maturity, number of filled grains and total number of grains. Meanwhile, all the traits differed significantly for genotype × environment (G×E) except number of tillers per hill and number of panicles per hill. Low heritability (<30%) was found for all the traits. Similarly, low genetic advance was also observed for all the traits except for number of tillers per hill and number of panicles per hill. yield per hectare had significant and positive correlation with most evaluated traits except for days to flowering, days to maturity, plant height and number of unfilled grains. Cluster analysis classified the 19 evaluated genotypes into six groups. Therefore, the six clusters/groups of genotypes were recommended as varieties for commercial cultivation in Malaysia and other rice growing regions.

Deciphering the Genetic Basis of Lodging Resistance in Wild Rice Oryza longistaminata.

The abuse of fertilizer results in tall rice plants that are susceptible to lodging and reduced plant yield. Hence, it is important to identify and utilize the quantitative trait loci (QTLs)/genes for lodging resistance breeding. Oryza longistaminata exhibits a strong stem and high biomass productivity, which could be a candidate gene pool for cultivars lodging resistance improvement. Here, a set of 152 BC2F20 lines derived from a cross between a cultivated line 93-11 and O. longistaminata was evaluated for lodging resistance. QTL mapping analysis combined with single-nucleotide polymorphism (SNP) marker derived from high-throughput sequencing identified 12 QTLs for stem diameter (SD), 11 QTLs for stem length (SL), and 3 QTLs for breaking strength (BS). Of which, 14 QTLs were first identified from O. longistaminata. A major QTL, qLR1, which was delimited to a region ∼80 kb on chromosome 1, increased stem diameter, stem length, and breaking strength. Another major QTL, qLR8, that was delimited in an interval ∼120 kb on chromosome 8, significantly enhanced the breaking strength. These results provide evidence that O. longistaminata can be exploited to develop lodging-resistant rice lines.

Gene expression studies in bacterial leaf blight resistant and susceptible rice (Oryza sativa) lines

Bacterial leaf blight of rice is a major constraint in tumbling productivity of the crop which shows the precarious nature of the disease. Host resistance is an effective strategy for the management of bacterial leaf blight disease over the cultural, chemical and biological management methods. Glass house and field studies were performed during 2017–19 at Paddy Breeding Station, TNAU, Coimbatore and also the molecular laboratory facility at Department of Plant Pathology was utilized. The objective of the study was to perform gene expression studies resistance genes (Xa21, xa5, xa13 genes) and defense genes (LOX and PAL) in bacterial leaf blight resistance (IRBB 60) and susceptible rice line (TN1) after application of Xanthomonas oryzae. pv. oryzae and/or riboflavin. Genotyping of IRBB 60 which showed lowest lesion length validated the presence of Xa21, xa5 and xa13 resistance genes using corresponding gene specific primers. Application of riboflavin (0.5mM) along with the Xanthomonas oryzae. pv. oryzae suspension resulted in the highest expression level of these R genes and defense genes except xa13 gene which showed its highest expression level with the inoculation of Xoo alone. Expression of Xa13 gene was meagre with the treatment of riboflavin where rest of the gene expression was noticeably enhanced when compared to the control. In brief, study performed showed that application of abiotic agent (Riboflavin) enhanced the gene expression of both the resistance and defense gene in rice line when compared to the susceptible variety.