Phenotypic evaluation of advanced breeding lines of Jagtial Vari 3 (JGL 27356) for bacterial leaf blight resistance in rice (Oryza sativa L.)

Introduction

Rice (Oryza sativa L.) is the principal staple food for more than half of the world's population and plays a vital role in global food security. India is one of the largest producers of rice, cultivating the crop over diverse agro-climatic regions. However, rice productivity is severely constrained by several biotic stresses, among which bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. Oryzae (Xoo) is one of the most devastating diseases (Nino-Liu et al., 2006) [10] . Under favourable environmental conditions, the disease can result in yield losses ranging from 20 to 80%, depending on cultivar susceptibility, crop growth stage and pathogen virulence (Ou, 1985; Mew et al., 1993) [11,9] . Though the chemical control measures provide temporary suppression of the disease, they are economically expensive, environmentally undesirable and often ineffective due to the emergence of new pathogenic races (Mew, 1987; Verdier et al., 2012) [8,16] . Therefore, host plant resistance remains the most economical, sustainable and environmentally safe approach for BLB management (Khush and Angeles, 1999) [7] . More than forty BLB resistance genes have been identified in rice (Chen et al., 2020) [1] , among which Xa21 is one of the most widely utilized dominant genes because of its broad-spectrum resistance against diverse Xoo races (Song et al., 1995; Ronald et al., 1992) [14,13] . Among these, several genes including Xa1, xa5, Xa4, xa13, Xa21, Xa23, Xa25, Xa26 (Xa3), Xa27, Xa10 and xa41 have been cloned and functionally characterized (Jiang et al., 2020) [5] . Marker-assisted breeding has significantly accelerated the development of disease-resistant rice cultivars by enabling precise introgression of target genes while minimizing the linkage drag. Phenotypic validation under artificial disease pressure is indispensable for confirming the effectiveness of introgressed resistance genes, because molecular marker-assisted selection alone cannot fully assess the expression and durability of resistance under field conditions International Journal of Advanced Biochemistry Research 2026; SP-10(8): 893-896 (Kauffman et al., 1973; IRRI, 2013) [6,4] . Therefore, the present study was undertaken to evaluate advanced breeding lines of JGL 27356 for resistance to bacterial leaf blight under artificial inoculation and to identify promising resistant lines for their utilization in future rice improvement programmes.

Materials and Methods

The present investigation was conducted during Kharif 2025 at Rice Research Unit (RRU), Agricultural Research Institute (ARI), Rajendranagar, Hyderabad, to evaluate the advanced breeding lines of rice (Oryza sativa L.) for resistance to bacterial leaf blight (BLB). The experimental material is comprised of 50 advanced breeding lines (F₆ generation) developed from the cross between JGL 27356 (Jagtial Vari 3) and MTU1010NIL For phenotypic screening, the breeding lines were evaluated along with its recurrent parent (JGL 27356), Taichung Native 1 (TN1) as the susceptible check and Improved Samba Mahsuri (ISM) as the resistant check. A virulent isolate of Xanthomonas oryzae pv. oryzae (Xoo), which was obtained from the ICAR-Indian Institute of Rice Research (ICAR-IIRR), Rajendranagar, Hyderabad, was cultured on Hayward's agar medium and incubated at 28°C for 96 hours. The bacterial cells were harvested and suspended in sterile distilled water to obtain an inoculum concentration of approximately 10⁸-10⁹ CFU mL⁻¹. Artificial inoculation was performed at the maximum tillering stage (approximately 55 days after transplanting) by following the leaf clipping method as described by Kauffman et al. (1973) [6] , wherein the terminal 1-2 cm portion of fully expanded uppermost leaves was clipped using scissors, which were dipped in the bacterial suspension. Approximately ten leaves per plant were inoculated to ensure uniform disease development. Disease severity was assessed 21 days after inoculation by recording lesion length and total leaf length. The percentage of disease incidence was calculated using the formula: Disease incidence (%) = (Lesion length / Leaf length) × 100

The disease reaction was classified according to the IRRI Standard Evaluation System (SES, 2013) [4] as follows (Table -1

Discussion

The development of rice cultivars possessing durable resistance to bacterial leaf blight (BLB) through markerassisted breeding has become an effective strategy for minimizing the yield losses caused by Xanthomonas oryzae pv. oryzae (Xoo). Among the identified BLB resistance genes, Xa21 has been widely utilized because of its broadspectrum resistance against diverse pathogen races (Song et al., 1995) [14] . Several studies have demonstrated that introgression of Xa21, either alone or in combination with other resistance genes will provide an effective protection against bacterial leaf blight under both artificial and natural field conditions. Similar observations were reported by Sundaram et al. (2008) [15] , who demonstrated the markerassisted pyramiding of bacterial blight resistance genes, including Xa21, into an elite rice variety Samba Mahsuri, which resulted in broad-spectrum and durable resistance against diverse races of Xanthomonas oryzae pv. oryzae.

Hari et al. (2013) [3] , who successfully introgressed Xa21 into elite rice cultivars and observed enhanced resistance under artificial screening. Similar results were also documented by Laxmi Prasanna et al. (2018) [12] , who reported that breeding lines carrying Xa21, consistently exhibited lower lesion lengths and reduced disease severity, when compared with susceptible parental lines. Gautam et al. (2023) [2] demonstrated that pyramiding of Xa21, xa13, xa5 and Xa4 through marker-assisted backcross breeding produced rice lines, that exhibited durable bacterial blight resistance across multiple environments and also highlighted the continued effectiveness of Xa21 in combination with other resistance genes.

The recovery of resistant and moderately resistant individuals in the advanced generation suggests the successful incorporation of the Xa21 gene into selected breeding lines through marker-assisted pedigree breeding. Nevertheless, the predominance of susceptible lines indicates segregation of resistance loci and highlights the importance of combining molecular marker-assisted selection with phenotypic screening to identify true resistant recombinants.

Conclusion

The present investigation demonstrates a substantial variability among advanced breeding lines for bacterial leaf blight resistance under artificial inoculation. Among the 50 advanced F₆ breeding lines, VPN-31 exhibited a resistant reaction comparable to the resistant check Improved Samba Mahsuri, whereas VPN-29, VPN-43 and VPN-50 expressed moderate resistance. These breeding lines of F6 generation represent valuable genetic resources for the development of high-yielding rice cultivars with durable resistance to bacterial leaf blight. Further multilocation evaluation, molecular confirmation and agronomic assessment are recommended before their utilization in varietal release programmes or as donor parents in future rice improvement programmes.

Acknowledgement

AcknowledgementI gratefully acknowledge College of Agriculture, Professor Jayashankar Telangana Agricultural University (PJTAU), Hyderabad, for providing financial assistance that supported the successful completion of my research and I also express my sincere gratitude to Rice Research Unit (RRU), Agricultural Research Institute (ARI), Rajendranagar, Hyderabad, for providing the necessary field and research facilities to conduct the experimental work and disease screening.

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