Identification, pathogenicity, and fungicide sensitivity of Eutiarosporella dactylidis associated with leaf blight on maize in China

Maize(Zea mays L.) is an economically vital grain crop that is cultivated worldwide. In 2011, a maize foliar disease was detected in Lingtai and Lintao counties in Gansu Province, China. The characteristic signs and symptoms of this disease include irregular chlorotic lesions on the tips and edges of infected leaves and black punctate fruiting bodies in dead leaf tissues. Given favourable environmental conditions, this disease spread to areas surrounding Gansu. In this study, infected leaves were collected from Gansu and Ningxia Hui Autonomous Region between 2018and 2020 to identify the disease-causing pathogen. Based on morphological features, pathogenicity tests, and multilocus phylogenetic analysis involving internal transcribed spacer(ITS), 18S small subunit rDNA(SSU), 28S large subunit rDNA(LSU), translation elongation factor 1-alpha(TEF), and β-tubulin(TUB) sequences, Eutiarosporella dactylidis was identified as the causative pathogen of this newly discovered leaf blight. Furthermore, an in vitro bioassay was conducted on representative strains using six fungicides, and both fludioxonil and carbendazim were found to significantly inhibit the mycelial growth of E. dactylidis. The results of this study provide a reference for the detection and management of Eutiarosporella leaf blight.

Development of Spectral Features for Monitoring Rice Bacterial Leaf Blight Disease Using Broad-Band Remote Sensing Systems

As an important rice disease, rice bacterial leaf blight (RBLB, caused by the bacterium Xanthomonas oryzae pv.oryzae), has become widespread in east China in recent years. Significant losses in rice yield occurred as a result ofthe disease’s epidemic, making it imperative to monitor RBLB at a large scale. With the development of remotesensing technology, the broad-band sensors equipped with red-edge channels over multiple spatial resolutionsoffer numerous available data for large-scale monitoring of rice diseases. However, RBLB is characterized by rapiddispersal under suitable conditions, making it difficult to track the disease at a regional scale with a single sensorin practice. Therefore, it is necessary to identify or construct features that are effective across different sensors formonitoring RBLB. To achieve this goal, the spectral response of RBLB was first analyzed based on the canopyhyperspectral data. Using the relative spectral response (RSR) functions of four representative satellite or UAVsensors (i.e., Sentinel-2, GF-6, Planet, and Rededge-M) and the hyperspectral data, the corresponding broad-bandspectral data was simulated. According to a thorough band combination and sensitivity analysis, two novel spectralindices for monitoring RBLB that can be effective across multiple sensors (i.e., RBBRI and RBBDI) weredeveloped. An optimal feature set that includes the two novel indices and a classical vegetation index was formed.The capability of such a feature set in monitoring RBLB was assessed via FLDA and SVM algorithms. The resultdemonstrated that both constructed novel indices exhibited high sensitivity to the disease across multiple sensors.Meanwhile, the feature set yielded an overall accuracy above 90% for all sensors, which indicates its cross-sensorgenerality in monitoring RBLB. The outcome of this research permits disease monitoring with different remotesensing data over a large scale.

In Vitro Efficacy Assessment of Botanical Extracts against Botrytis gladiolorum Causing Gladiolus Leaf Blight

An experiment was conducted at the Mycology laboratory, Department of Plant Pathology, Sher-e-Bangla Agricultural University, Dhaka, Bangladesh to find out the efficacy of selected botanical extracts against Botrytis gladiolorum (Bg) causing gladiolus leaf blight. Infected leaves samples were collected from gladiolus farmers’ field and brought to the laboratory for study. Ten selected botanicals were used against the colony growth of (Bg). The botanicals were Mehendi, Chrysanthemum, Basil (Tulsi), Onion, Neem, Bael, Arjuna, Garlic, Aloevera (Ghritkumary) and Turmeric. Botanical extracts were applied at the rate of 5%, 10% and 20%. The radial mycelia growth was found minimum (11.60 mm) in garlic extract treated plate at the dose of 5% at 5 DAI, which was statistically similar with turmeric extract treated (14.00 mm) plate and the inhibition of growth was 60% and 51.72%, respectively. Similar trend was found at 10 DAI and 15 DAI. At 15 DAI, garlic and turmeric extract gave the best result against Bg, which was statistically similar with onion (50.07% inhibition) and mehendi (49.93%). All botanicals showed significantly different results over control and found effective in reducing the mycelial growth at the dose of 10%. At 5 DAI, no radial mycelia growth was found in garlic treated plate, which was statistically similar with onion treated plate, means that the inhibition of growth was 100%. Similar trend was also found at 10 DAI, and 15 DAI but at 15 DAI, onion (30.20 mm) gave the statistically similar results with Garlic (30.10 mm) and the mycelia growth inhibition was (57.70%) and (57.84%), respectively. In case of 20% dose, garlic extract showed the best result at 5 DAI and the radial mycelia growth was found minimum (00.00 mm) which was statistically similar with onion extract treated (00.00 mm) plate and turmeric extract treated plate. The inhibition of growth was 100%. At 15 DAI, the inhibition of fungal growth was found (73.74%), (71.23%) and (66.90%), respectively with treated by turmeric (18.80 mm), garlic (20.60 mm) and onion (23.70 mm).

Exploring the nano-fungicidal efficacy of green synthesized magnesium oxide nanoparticles(MgO NPs)on the development,physiology,and infection of carrot(Daucus carota L.)with Alternaria leaf blight(ALB):Molecular docking

In this research,green synthesized magnesium oxide nanoparticles(MgO NPs)from lemon fruit extracts and their fungicidal potential was evaluated against Alternaria dauci infection on carrot(Daucus carota L.)under greenhouse conditions.The scanning and transmission electron microscopy(SEM and TEM)and ultra-violet(UV)visible spectroscopy were used to validate and characterize MgO NPs.The crystalline nature of MgONPs was determined using selected area electron diffraction(SAED).MgO NPs triggered substantial antifungal activity against A.dauci when exposed to 50 and 100 mg L^(–1)concentrations but the higher antifungal potential was noticed in 100 mg L^(–1)under invitro conditions.In fungal inoculated plants,a marked decrease in growth,photosynthetic pigments,and an increase in phenol,proline contents,and defense-related enzymes of carrot were seen over control(distilled water).However,foliar application of MgO NPs at 50 and 100 mg L^(–1)resulted in significant improvement of plant growth,photosynthetic pigments,phenol and proline contents,and defense enzymes activity of carrots with and without A.dauci infection.Spraying of MgO NPs at 100 mg L^(–1)had more plant length(17.11%),shoot dry weight(34.38%),plant fresh weight(20.46%),and root dry weight(49.09%)in carrots when challenged with A.dauci over inoculated control.The leaf blight indices and percent disease severity were also reduced in A.dauci inoculated plants when sprayed with MgO NPs.The non-bonding interactions of Alternaria genus protein with nanoparticles were studied using molecular docking.

In vitro and in silico studies of salicylic acid on systemic induced resistance against bacterial leaf blight disease and enhancement of crop yield

Salicylic acid(SA)is an effective elicitor to promote plant defenses and growth.This study aimed to investigate rice(Oryza sativa L.)cv.Khao Dawk Mali 105 treated with salicylic acid(SA)-Ricemate as an enhanced plant protection mechanism against bacterial leaf blight(BLB)disease caused by Xanthomonas oryzae pv.oryzae(Xoo).Results indicated that the use of SA-Ricemate as a foliar spray at concentrations of more than 100 mg L^(-1)can reduce the severity of BLB disease by 71%.SA-Ricemate treatment also increased the hydrogen peroxide(H_(2)O_(2))content of rice leaf tissues over untreated samples by 39–61%.Malondialdehyde(MDA)in rice leaves treated with SA-Ricemate also showed an increase of 50–65%when comparing to non-treated samples.The differential development of these defense compounds was faster and distinct when the SA-Ricemate-treated rice was infected with Xoo,indicating plant-induced resistance.Besides,SA-Ricemate elicitor at a concentration of 50–250 mg L^(-1)was correlated with a substantial increase in the accumulation of total chlorophyll content at 2.53–2.73 mg g^(-1)of fresh weight which suggests that plant growth is activated by SA-Ricemate.The catalase-and aldehyde dehydrogenase-binding sites were searched for using the CASTp server,and the findings were compared to the template.Chemsketch was used to design and optimize SA,which was then docked to the catalase and aldehyde dehydrogenase-binding domains of the enzymes using the GOLD 3.0.1 Software.SA is shown in several docked conformations with the enzymes catalase and aldehyde dehydrogenase.All three catalase amino acids(GLN7,VAL27,and GLU38)were discovered to be involved in the creation of a strong hydrogen bond with SA when SA was present.In this mechanism,the aldehyde dehydrogenase amino acids LYS5,HIS6,and ASP2 were all implicated,and these amino acids created strong hydrogen bonds with SA.In field conditions,SA-Ricemate significantly reduced disease severity by 78%and the total grain yield was significantly increased which was an increase of plant height,tiller per hill,and panicle in three field trials during Aug–Nov 2017 and 2018.Therefore,SA-Ricemate can be used as an alternative elicitor on replacing harmful pesticides to control BLB disease with a high potential of increasing rice defenses,growth,and yield components.

Identification and Evaluation of Particular Corn Hybrids with Resistance against Corn Northern Leaf Blight

[ Objective] The paper was to evaluate the resistance of particular corn hybrids against northern leaf blight. [ Method ] Using artificial inoculation meth- od, the resistance of 238 copies of particular corn hybrids including silage corn, high oil corn, waxy corn and sweet corn against northern leaf blight was evaluated. [ Result] The corn samples with high resistance, resistance, moderate resistance, susceptibility and high susceptibility to northern leaf blight among 238 copies of materials in identification accounted for 0.8%, 20.6%, 44. 1%, 24.8% and 9.7%, respectively. Different types of varieties had significant difference in resist- ance. Among cern varieties with moderate resistance or higher level, silage corn accounted for 87.8% ; high oil corn and waxy corn accounted for 73.3% and 61.3 %, respectively; sweet corn was less, accounting for 44.2%. Sixteen of 30 approved particular corn varieties showed resistance, accounting for 53.3 % of total approved varieties. [Condusion] The paper provided theoretical basis for breeding and planting of particular corn hybrids with resistance against northern leaf blight.

Biological characters and rDNA ITS sequences of pathogen of poplar leaf blight

DNA was extracted from the strain of pathogen of poplar leaf blight using a modified CTAB method. ITS sequence （601bp） was initially amplified from the pathogen by using the universal primers ITSl and ITS4 （registered No, DQ011257）. Comparing to the nucleotide sequences acquired from GenBank database, the strain is clustered into the homogeneity with Alternaria alternate （AY787684） and Alternaria alternate （AY354228）, with a homology of 98%, thus the strain was checked as Alternaria alternata （Fr.） Keissler. The optimal conditions for conidia germination and mycelium growth of the pathogen were tested, The optimal temperature for conidia germinating and mycelium growth is 25℃, and the optimal pH value is 6. Mycelium grows rather slowly at 10℃ and 30℃ and growth stops at above 35 ℃. Among the six culture mediums tested, PDA ＋ poplar leaf juice medium is most favorable for mycelium growth.

Hybrid Rice Resistant to Bacterial Leaf Blight Developed By Marker Assisted Selection

Through recurrent backcrossing in combination with molecular marker-assisted selection (MAS), restorer lines R8006 and Rl176 carrying Xa-21, a gene having broad-spectrum resistance to rice bacterial leaf blight, were selected. By crossing the two lines to CMS line Zhong 9A, two new hybrid rice combinations, Zhongyou 6 and Zhongyou 1176 were developed. The hybrids showed high resistance to diseases, good grain quality and high yielding potential in national and provincial adaptability and yield trials.

Intelligent diagnosis of northern corn leaf blight with deep learning model

Maize(Zea mays L.), also known as corn, is the third most cultivated crop in the world. Northern corn leaf blight(NCLB) is a globally devastating maize foliar disease caused by Setosphaeria turcica(Luttrell) Leonard and Suggs. Early intelligent diagnosis and warning is an effective and economical strategy to control this disease. Today, deep learning is beginning to play an essential role in agriculture. Notably, deep convolutional neural networks(DCNN) are amongst the most successful machine learning techniques in plant disease detection and diagnosis. Our study aims to identify NCLB in the maize-producing area in Jilin Province based on several DCNN models. We established a database of 985 leaf images of healthy and infected maize and applied data augmentation techniques including image segmentation, image resizing, image cropping, and image transformation, to expand to 30 655 images. Several proven convolutional neural networks, such as AlexNet, Google Net, VGG16, and VGG19, were then used to identify diseases. Based on the best performance of the DCNN pre-trained model Google Net, some of the recent loss functions developed for deep facial recognition tasks such as Arc Face, Cos Face, and A-Softmax were applied to detect NCLB. We found that a pre-trained Google Net architecture with the Softmax loss function can achieve an excellent accuracy of 99.94% on NCLB diagnosis. The analysis was implemented in Python with two deep learning frameworks, Pytorch and Keras. The techniques, training, validation, and test results are presented in this paper. Overall, our study explores intelligent identification technology for NCLB and effectively diagnoses NCLB from images of maize.

Research Progress on Northern Leaf Blight in Corn

The northem corn leaf blight is one of the most serious diseases in maize production. The research progress on etiology, generation law and control strategy, antigen identification, resistance mechanism and inheritance of this disease was discussed. And the research work which should be enhanced in China was pointed out, such as mechanism of resistance inheritance, developing function marker, gene mining, screening resistance resource and dominant physiological race in different areas.

Evaluation of Inherited Resistance Genes of Bacterial Leaf Blight, Blast and Drought Tolerance in Improved Rice Lines

Improved rice lines were developed frome three parents with the resistance or tolerance to bacterial leaf blight,blast and drought stress,respectively,using single-,double-and three-way crosses.The improved lines were assessed for agro-morphological and yield traits under non-drought stress(NS)and reproductive-stage drought stress(RS)treatments.The mean comparison of traits measured between parent plants and progenies(improved lines)were similar,and there were significant and non-significant differences among the parents and improved lines(genotypes)under NS and RS.Smilarly,there was significant and non-significant differences in the interaction among both parent varieties and improved lines for NS and RS.Cluster and 3D-model of principal component analysis did not generate categorical clusters according to crossing methods,and there were no exclusive crossing method inclined variations under the treatments.The improved lines were high-yielding,disease resistant,and drought-tolerant compared with their parents.All the crossing methods were good for this crop improvement program without preference to any,despite the number of genes introgressed.

Field Control Efficacy of Several Reagents against Northern Leaf Blight of Maize(Exserohilum turcicum)

[Objective] The paper was to screen suitable agents for controlling northern leaf blight of maize in field. [Method] Field efficacy test was conducted using the agents of propiconazole, azoxystrobin, propiconazole·azoxystrobin, coumoxystrobin·tebuconazole, coumoxystrobin·tebuconazole and azoxystrobin. [Result] At 14 d post secondary spraying, the control effects of 25% propionazole EC 168.8 g/hm^2, 25% azoxystrobin SC 300 g/hm^2, 18.7% propiconazole·azoxystrobin SC 196.4 g/hm^2, 40% coumoxystrobin·tebuconazole SC 180 m L/hm^2, 40% coumoxystrobin·tebuconazole SC 180 m L/hm^2＋ 25% azoxystrobin SC 300 g/hm^2 against northern leaf blight of maize were 77.35%, 77.11%, 78.13%, 74.60% and 80.94%, re-spectively. The agents were safe and harmless to maize. [Conclusion] Considering the production factors, 18.7% propiconazole·azoxystrobin SC196.4 g/hm^2 or 40% coumoxystrobin·tebuconazole SC 180 m L/hm^2＋ 25% azoxystrobin SC 300 g/hm^2 can be sprayed in production before the incidence or in the initial incidence of northern leaf blight of maize.

Resistance to Bacterial Leaf Blight in a Somaclonal Rice Mutant HX-3 at Cellular Level

The interaction between rice host and its pathogen Xanthomonas oryzae pv. oryzae (Xoo) at cellular level was studied by using a resistant somaclonal mutant HX-3 and its susceptable donor Minghui 63. After inoculation with Xoo strain Zhe 173 (Chinese pathotype Ⅳ), the activity of superoxide dismutase (SOD) and peroxidase (POD) in the callus of Minghui 63 was increased dramatically, and the active oxygen(O2 ) was produced at a higher rate; Meanwhile, the callus grew slowly with the reduction of protein content Compared to the activity of SOD and POD, the production rate of Oa and the fresh weight in HX-3 callus varied little after the inoculation It could be proposed that there were great differences between the resistance of HX-3 and Mighui 63 at cellular level. There was no difference detected concerning resistance to bacterial leaf blight in HX-3 between the plant and the callus.

Isolating QTL controlling sugarcane leaf blight resistance using a two-way pseudo-testcross strategy

Sugarcane leaf blight(SLB),caused by Stagonospora tainanensis,is one of the most harmful fungal diseases,threatening the sugarcane industry and causing high losses of cane yield and sugar in susceptible cultivars.Using a two-way pseudo-testcross mapping strategy in combination with array genotyping,two high-density genetic maps were constructed for sugarcane cultivars YT93-159 and ROC22 with mean densities of respectively 3.0 and 3.5 cM per marker,and covering respectively 4485 and 2720 cM of genetic distance.The maps showed highly conserved colinearity with the genome of the ancestral species Saccharum officinarum,supporting the reliability of the linkage configurations of the maps.Quantitative trait loci(QTL)analysis of SLB resistance revealed six QTL(qSLB-1–qSLB-6).The major QTL qSLB-1 explaining 16.4%of phenotypic variance was assigned as the main QTL,and the total percentages of phenotypic variance explained in YT93-159 and ROC22 were 37.9%and 17.6%,respectively.Nine transcription factor and seven pathogen receptor genes lying in the qSLB-1 interval were highly expressed and are proposed as candidate causal genes for SLB resistance.

RPA-Assisted Cas12a System for Detecting Pathogenic Xanthomonas oryzae,a Causative Agent for Bacterial Leaf Blight Disease in Rice

Xanthomonas oryzae pv.oryzae(Xoo)is a widespread pathogen causing bacterial leaf blight(BLB)disease,devastating rice productivity in many cultivated areas of Thailand.A specific and simple method for Xoo detection is required to improve surveillance of disease transmission and outbreak.This study developed a recombinase polymerase amplification(RPA)assay assisted with CRISPR-cas12a assay(RAC)for Xoo detection from bacterial cell suspension of infected rice samples without DNA extraction.The efficiency of the RAC system for Xoo detection using either Xoo80 or Xoo4009 locus was optimized to amplify and determine the sensitivity and specificity using a Xoo DNA template from bacterial cell suspension of infected rice samples without DNA extraction.The RAC system using the Xoo4009 locus gave a higher specificity than Xoo80 locus,because only Xoo species was amplified positive RPA product with fluorescence signal by cas12a digestion,which indicated no cross reactivity.Optimal RAC using the Xoo4009 locus enabled diagnosis of Xoo presence from both plant extracted samples of Xoo artificially inoculated rice leaves within 3 d post-inoculation without symptomatic BLB appearance,and Xoo naturally infected rice.Findings exhibited that RAC using the Xoo4009 locus offered sensitivity,specificity and simplicity for Xoo detection,with low intensities of Xoo-DNA(1×10^(3) copies/μL)and Xoo-cell(2.5×10^(3) cfu/mL).This developed RAC system showed significantly potential for Xoo detection at point-of-care application for early signs of BLB disease outbreak in rice fields.

Distribution,Etiology,Molecular Genetics and Management Perspectives of Northern Corn Leaf Blight of Maize(Zea mays L.)

Maize is cultivated extensively throughout the world and has the highest production among cereals.However,Northern corn leaf blight(NCLB)disease caused by Exherohilum turcicum,is the most devastating limiting factor of maize production.The disease causes immense losses to corn yield if it develops prior or during the tasseling and silking stages of crop development.It has a worldwide distribution and its development is favoured by cool to moderate temperatures with high relative humidity.The prevalence of the disease has increased in recent years and new races of the pathogen have been reported worldwide.The fungus E.turcicum is highly variable in nature.Though different management strategies have proved effective to reduce economic losses from NCLB,the development of varieties with resistance to E.turcicum is the most efficient and inexpensive way for disease management.Qualitative resistance for NCLB governed by Ht genes is a race-specific resistance which leads to a higher level of resistance.However,some Ht genes can easily become ineffective under the high pressure of virulent strains of the pathogen.Hence,it is imperative to understand and examine the consistency of the genomic locations of quantitative trait loci for resistance to NCLB in diverse maize populations.The breeding approaches for pyramiding resistant genes against E.turcicum in maize can impart NCLB resistance under high disease pressure environments.Furthermore,the genome editing approaches like CRISPR-cas9 and RNAi can also prove vital for developing NCLB resistant maize cultivars.As such this review delivers emphasis on the importance and current status of the disease,racial spectrum of the pathogen,genetic nature and breeding approaches for resistance and management strategies of the disease in a sustainable manner.

Phenotypic and Molecular Assessment of Wheat Genotypes Tolerant to Leaf Blight,Rust and Blast Diseases

Globally among biotic stresses,diseases like blight,rust and blast constitute prime constraints for reducing wheat productivity especially in Bangladesh.For sustainable productivity,the development of disease-resistant lines and high yielding varieties is vital and necessary.This study was conducted using 122 advanced breeding lines of wheat including 21 varieties developed by Bangladesh Wheat and Maize Research Institute with aims to identify genotypes having high yield potential and resistant to leaf blight,leaf rust and blast diseases.These genotypes were evaluated for resistance against leaf blight and leaf rust at Dinajpur and wheat blast at Jashore under field condition.Out of 122 genotypes tested,20 lines were selected as resistant to leaf blight based on the area under the diseases progress curve under both irrigated timely sown and irrigated late sown conditions.Forty-two genotypes were found completely free from leaf rust infection,59 genotypes were identified as resistant,and 13 genotypes were identified as moderately resistant to leaf rust.Eighteen genotypes were immune against wheat blast,42 genotypes were categorized as resistant,and 26 genotypes were identified as moderately resistant to wheat blast.Molecular data revealed that the 16 genotypes showed a positive 2NS segment among the 18 immune genotypes selected against wheat blast under field conditions.The genotypes BAW 1322,BAW 1295,and BAW 1203 can be used as earlier maturing genotypes and the genotypes BAW 1372,BAW 1373,BAW 1297 and BAW 1364 can be used for lodging tolerant due to short plant height.The genotypes WMRI Gom 1,BAW 1349 and BAW 1350 can be selected for bold grain and the genotypes WMRI Gom 1,BAW 1297,BAW 1377 can be used as high yielder for optimum seeding condition but genotypes BAW 1377 and BAW 1366 can be used for late sown condition.The selected resistant genotypes against specific diseases can be used in the further breeding program to develop wheat varieties having higher disease resistance and yield potential.

Nutritional Elements Related to Leaf Blight of Pearl Plum in Longtan Town

[Objectives]This study was conducted to investigate the correlation between leaf blight of pearl plum and nutrient elements from the perspective of plant nutrition.[Methods]Branch and leaf samples of pearl plum plants infected by or free of leaf blight and the corresponding 0-30 cm cultivated soil were collected,and statistical analysis was conducted according to the changes in nutrient contents and the incidence of leaf blight,so as to look for nutrients in pearl plum plants associated with leaf blight,as well as soil constraint factors.[Results]Phosphorus,iron and manganese in nutrients may be related to leaf blight,and the factors affecting leaf blight may be the ratios of P/Fe and P/Mn in leaves.[Conclusions]This study provides a basis for further research on the relationship between phosphorus,iron and manganese on the effect of leaf blight in pearl plum trees.

Molecular Detection of Phytophthora colocasiae of Taro Leaf Blight Based on PCR

The present PCR assay was conducted to develop rapid and sensitive detection of Phytophthora colocasiae,in order to provide a robust and reliable tool for healthy seedling production of taro and limiting the transmission and spread of the causal organism of taro leaf blight in taro planting regions.The samples were used to extract total DNA and to be detected by PCR with P.colocasiae specific primer pairs PCSP-RL F/PCSP-RL R and PCSP-T F/PCSP-T R,respectively.Distinct fragments of about 200 bp and 240 bp were amplified by PCR using primers PCSP-RL F/PCSP-RL R and PCSP-T F/PCSP-T R,respectively.The analysis of the nucleotide sequence of the PCR products were found to be 99% identical to sequence of RAS-related protein (Ypt1) and phospho-ribosylanthranilate isomerase (TRP1) in P.colocasiae,respectively.It is concluded that rapid and sensitive developed PCR assay for detection of P.colocasiae could be used in routine diagnosis and aid in management practices to mitigate taro leaf blight.

Marker-Assisted Selection of Xa21 Conferring Resistance to Bacterial Leaf Blight in indica Rice Cultivar LT2

Bacterial leaf blight of rice (BLB), caused by Xanthomonas oryzae pv. oryzae, is one of the most destructive diseases in Asian rice fields. A high-quality rice variety, LT2, was used as the recipient parent.IRBB21, which carries the Xa21 gene, was used as the donor parent. The resistance gene Xa21 was introduced into LT2 by marker-assisted backcrossing. Three Xoo races were used to inoculate the improved lines following the clipping method. Eleven BC_3F_3 lines carrying Xa21 were obtained based on molecular markers and agronomic performance. The 11 lines were then inoculated with the three Xoo races. All the 11 improved lines showed better resistance to BLB than the recipient parent LT2. Based on the level of resistance to BLB and their agronomic performance, five lines (BC_3F_3 5.1.5.1, BC_3F_3 5.1.5.12, BC_3F_3 8.5.6.44, BC_3F_3 9.5.4.1 and BC_3F_3 9.5.4.23) were selected as the most promising for commercial release. These improved lines could contribute to rice production in terms of food security.