Characterisation of advanced breeding lines for bacterial leaf blight resistance by morpho-molecular screening in rice (Oryza sativa L.)

Morphological and Molecular Screening for Bacterial Leaf Blight Resistance in Land Races of Rice (Oryza sativa L.)

Bacterial leaf blight (BLB) of rice, caused by Xanthomonas oryzae pv. oryzae, is a major constraint on rice production, and the use of resistant genotypes is an important approach to disease management. The present study screened 40 rice genotypes for BLB resistance using morphological evaluation and molecular markers linked to seven resistance genes: xa5, Xa7, xa8, Xa10, xa13, Xa21 and Xa33. Field screening was conducted at RARS, Maruteru, during kharif 2023 using artificial inoculation by the leaf-clipping method, and disease reactions were assessed according to the Standard Evaluation System. Morphological screening categorised entries as highly resistant, resistant, moderately resistant, susceptible or highly susceptible according to diseased leaf area. Molecular screening was performed using gene-linked markers to determine the presence of the target resistance genes. Nineteen genotypes were identified as carrying two or three BLB resistance genes. Phenotypic evaluation based on diseased leaf area showed variation in resistance among the 40 genotypes and supported the molecular screening results. Jaavepula-2, Basmati, Tulasi baso and Kundadam-2 carried three resistance genes, while Kalamuch and Loyamalli carried the Xa7 and Xa21 combination and exhibited phenotypic resistance. The combined morphological and molecular screening therefore identified rice genotypes with multiple BLB resistance genes that may serve as donor parents in marker-assisted breeding programmes aimed at improving BLB resistance in rice.

Genetics and Resistance / Génétique et Résistance Genetic mapping and marker development for the leaf rust resistance gene Lr30 in wheat ( Triticum aestivum L.)

Evaluation of Local Rice Genotypes from Southwest Aceh for Resistance to Bacterial Leaf Blight (Xoo Strain VIII)

Local rice germplasm is a valuable genetic resource for developing bacterial leaf blight (BLB)-resistant and high-yielding rice cultivars. However, information on the resistance of Southwest Aceh local rice to Xanthomonas oryzae pv. oryzae (Xoo), particularly during the generative stage, remains limited. Previous studies have mainly focused on commercial cultivars or vegetative-stage screening, leaving the resistance potential of local germplasm at the reproductive stage largely unexplored. This study aimed to evaluate the resistance of local rice to BLB at the generative stage of plant growth. The research was conducted at Experimental Field, Teuku Umar University. West Aceh (4°08′33″ N; 96°11′54″ E). Fifteen local rice genotypes, together with resistant and susceptible control varieties, were evaluated following artificial inoculation with Xoo strain VIII. Disease resistance was assessed based on incubation period and lesion length, while agronomic performance was evaluated using key yield-related traits. Seven local genotypes Itam Tangke Lango, Jantong, Jempa Puteh, Manyam U, Pade Manggeng-1, Pade Manggeng-2, and Rangan Lango were classified as resistant based on lesion length. Among the evaluated genotypes, Sikleng exhibited superior agronomic performance, producing the highest number of productive tillers (27.50) and grains per panicle (317.73). The novelty of this study lies in evaluating Southwest Aceh local rice germplasm for bacterial leaf blight resistance at the generative stage using Xoo strain VIII while integrating disease resistance with yield-related agronomic traits. The identified resistant genotypes provide valuable donor parents for breeding BLB-resistant, high-yielding rice cultivars and contribute to sustainable rice production and regional food security.

Marker-assisted Pyramiding of Bacterial Blight Resistance Genes into ‘Uma’, an Elite Red Rice Variety of Kerala

Background: Uma is a high-yielding, popular red-kernelled rice variety of Kerala; however, the occurrence of BB disease often causes severe yield reductions in this cultivar. Host plant resistance based on multiple genes is the most effective measure to impart durable resistance. Hence, efforts were undertaken to introgress the resistance genes, xa 5, xa13 and Xa21, from a BB-resistant variety, ISM, into Uma, using the MABB approach. Methods: Foreground selection was carried out using markers RG 556 and xa5 SR for xa5, RG136 and xa13 promoter for xa13 and pTA248 for Xa21 genes, respectively. The identified R-gene-pyramided plant was subjected to background selection using rice microsatellite markers for recurrent parent genome recovery. The phenotypic evaluation for BB resistance was carried out using the leaf-clipping method following the IRRI standard evaluation system, SES. Result: Molecular analysis of the recurrent parent Uma revealed the endogenous presence of R gene xa 5. The evaluation of BC2F1 lines identified a single plant pyramided with three resistance genes, with xa13 and Xa21 in the heterozygous condition, exhibiting a recurrent parent genome recovery of 70.45% and kernel characteristics similar to those of the Uma. Concurrently, BC1F2 lines generated from the cross were phenotypically screened for BB resistance, also identifying resistance to moderate resistance lines to the BB pathogen. Further advancement of these backcross generations was proposed to isolate gene pyramids homozygous for the resistance genes, with near-complete recurrent parent genome recovery.

Development of KASP marker to enhance breeding efficiency for phytophthora blight resistance in sesame through QTL analysis.

BACKGROUND Phytophthora blight, caused by Phytophthora nicotianae, is a destructive disease that severely affects sesame (Sesamum indicum L.). Developing resistant cultivars remains the most effective management strategy. This study aimed to identify genomic regions associated with Phytophthora blight resistance and to develop molecular markers for use in sesame breeding. RESULTS Whole-genome resequencing (WGS) was performed for the resistant cultivar Geonbaek, the susceptible cultivar Milsung, and 99 recombinant inbred lines (RILs). Using a high-density genetic map, we identified a major resistance locus on chromosome 10, designated qPB10. The IM-ADD analysis defined a 0.51-Mb marker interval with an LOD score of 25.67, and a complementary binary-trait analysis independently detected the same locus at 75.10 cM. Genomic analysis of the target region revealed several immune-related genes, including clusters encoding nucleotide-binding leucine-rich repeat (NLR) proteins and other defense-associated factors. To utilize these findings in breeding, kompetitive allele-specific PCR (KASP) markers were developed based on sequence polymorphisms within the qPB10 interval. Validation using the RIL population and a diverse panel of sesame cultivars identified a robust marker that reliably discriminates resistant genotypes. CONCLUSION These findings establish qPB10 as the primary locus governing Phytophthora blight resistance in sesame. The KASP markers developed in this study enable efficient marker-assisted selection without the need for extensive disease phenotyping. These results provide a practical genomic resource for accelerated breeding of resistant cultivars and establish a foundation for future functional characterization of resistance mechanisms.

Identification of novel source and inheritance of resistance to bacterial wilt (Ralstonia solanacearum) in tomato (Solanum lycopersicum L.) for sustainable disease management

Bacterial wilt caused by Ralstonia solanacearum is a destructive disease severely restricting tomato (Solanum lycopersicum L.) productivity in tropical and subtropical regions. The purpose of this study was to identify novel sources of resistance and explicate the inheritance pattern of bacterial wilt resistance in tomato.  A total of 59 genotypes, including open-pollinated lines, hybrids and breeding accessions, were subjected to screening experiments during two consecutive seasons (2022–2023 and 2023–2024) under controlled net house conditions at Centurion University of Technology and Management and natural epiphytotic field conditions at Indian Institute of Horticultural Research - Central Horticultural Experiment Station , Bhubaneswar, India. Disease severity was evaluated using percent disease index (PDI) and area under disease progress curve (AUDPC). The open-pollinated cultivar ‘Utkal Kumari (BT-10)’ exhibited consistent high resistance, with significantly lower AUDPC values (<150 vs >1800 in susceptible checks) and high survival rates (90 %) across environments. Among others, tomato cultivars Arka Samrat, Arka Abhed and JK Desi, demonstrated significant resistance while genotypes such as Pusa Ruby and EW815 were consistently highly susceptible. A segregating F₂ population derived from a cross between resistant ‘BT-10’ and susceptible ‘Pusa Ruby’ exhibited continuous variation in disease response. Chi-square analysis revealed significant deviation from a 3:1 Mendelian segregation ratio (χ² = 72.30, P < 0.01), indicating a quantitative mode of inheritance. These findings highlight the potential of Utkal Kumari and allied resistant lines as donors for resistance breeding and emphasize the need to integrate robust phenotypic screening with molecular approaches for durable and strategic bacterial wilt management in tomato.