The study highlights the substantial spatial, morphological and molecular variability present in A. porri populations associated with onion purple blotch in Tamil Nadu and provides valuable baseline information for disease surveillance, resistance screening and the development of effective management strategies.
Abstract
Purple blotch caused by Alternaria porri is one of the most destructive diseases limiting small onion (Allium cepa L.) production in Tamil Nadu. To understand the prevalence and variability of the pathogen, a comprehensive survey was conducted during 2024 across major onion-growing regions of the state. Disease severity varied considerably among locations, with percent disease index (PDI) values ranging from 9.80–76.80 %, indicating the widespread occurrence of the disease under diverse agro-climatic conditions. A total of 31 isolates of A. porri were recovered from infected onion samples and characterised using cultural, morphological and molecular approaches. The isolates exhibited marked variability in colony characteristics, sporulation, conidial morphology and virulence, suggesting the existence of diverse pathogen populations within the state. Pathogenicity studies identified several highly virulent isolates capable of causing severe disease symptoms. Molecular characterisation based on internal transcribed spacer (ITS) sequencing confirmed the identity of the isolates, showing 90–100 % similarity with reference A. porri sequences available in the National Center for Biotechnology Information (NCBI) database. Species identity was further validated using Alt a1 gene-specific primers. Phylogenetic analysis revealed moderate genetic diversity among the isolates and grouped them into distinct clusters, reflecting their evolutionary relationships. The study highlights the substantial spatial, morphological and molecular variability present in A. porri populations associated with onion purple blotch in Tamil Nadu and provides valuable baseline information for disease surveillance, resistance screening and the development of effective management strategies.
Background: Bacterial leaf blight (BLB) is a major bacterial disease of rice, causing serious yield losses in endemic regions. Continuous surveillance and characterization of pathogen variability are essential for effective disease management. Methods: A roving survey was conducted during 2025 in major rice-growing areas of the Chengalpattu district, Tamil Nadu. Diseased samples were collected from different rice varieties and subjected to isolation using the maceration technique. The per cent disease index (PDI) was calculated and documented. Morphological, cultural, pathogenicity analysis and molecular characterization (16S rRNA sequencing) were performed to confirm the pathogen. Virulence variability among ten isolates was assessed using clip inoculation on rice variety CO51. Result: The disease severity ranged from 40 to 85%, with CO51 recording the highest susceptibility (85%) among the reported varieties. All the study isolates exhibited circular, smooth, yellow, mucoid colonies on Nutrient Agar and were Gram-negative rods. Pathogenicity tests reproduced typical BLB symptoms and fulfilled Koch’s postulates. Molecular analysis confirmed 100% similarity with Xanthomonas oryzae pv. oryzae in the database. Significant variation in virulence was observed, with isolate 1(YNX001) recording the highest PDI. The study confirmed the prevalence of virulent BLB strains in Chengalpattu district and highlights the need for integrated disease management strategies.
Yuvaraj Nandhikeswaran, Akshaya Subbaih Balamurali, Rageshwari Selvaraj et al.· Indian Journal of Agricultur...· 0 citations
Fungal diseases severely threaten rice productivity and food security across the Cauvery Delta. This study investigated the prevalence, morphological variation, pathogenicity, and molecular identities of three primary fungal pathogens Bipolaris oryzae, Pyricularia oryzae and Rhizoctonia solani collected across Tamil Nadu and Karaikal U.T. Field surveys revealed wide spatial variation in disease intensity, with maximum percent disease index (PDI) recorded for sheath blight (54.00% in Nannilam), blast (42.34% in Aduthurai) and brown spot (30.40% in Pattukkottai). In vitro characterisation of ten isolates per species demonstrated notable diversity in mycelial growth rates, colony pigmentation, conidial features, and sclerotial formation. Controlled greenhouse evaluations on susceptible rice cultivar BPT-5204 confirmed varying degrees of virulence among isolates, identifying Bo8 (mean PDI 28.95%), Pg7 (mean PDI 38.99%) and Rs6 (mean PDI 36.85%) as the most aggressive pathotypes for brown spot, blast, and sheath blight, respectively. PCR amplification and Sanger sequencing of the ribosomal DNA internal transcribed spacer (rDNA-ITS) region definitively confirmed species identities for the hyper-virulent isolates: B. oryzae Bo8 (558 bp; ON556554), P. oryzae Pg7 (541 bp; ON556555) and R. solani Rs6 (514 bp; ON556551). These characterised pathotypes provide critical reference strains for regional resistance breeding and targeted disease management strategies.
K. Balamurugan, K. Vigneshwaran, R. Livitha et al.· Plant cell biotechnology and...· 0 citations
Spot blotch caused by fungal pathogen Bipolaris sorokiniana (Sacc.) Shoemaker is an important fungal disease in warm and humid wheat growing condition. Study on pathogenic variability of B. sorokinianana isolates is limited in Nepal. Information based on host × pathogen interaction is a useful tool to devise the disease management strategy. Therefore, aggressiveness of total 36 single spore isolates of B. sorokiniana (27 isolates from terai, 7 isolates from mid hill and 2 isolates from high hill) of Nepal were evaluated on 14 days old seedling of RR-21 (susceptible check), Guatam (moderate resistant) and Chirya 3 (resistant check) under polyhouse condition. Results revealed highly significant isolate-by-variety interaction (P<0.001) for all the disease development traits, suggesting substantial variability in the pathogenicity of the isolates. Moreover, days to disease appearance, number of lesions per leaf and disease severity was highly correlated to Area Under Disease Progress Curve (AUDPC), illustrating those traits as an important indicator of disease development and pathogen aggressiveness. RR-21 exhibited susceptible to overall isolates response followed by Gautam and Chirya 3. On the basis of AUDPC value, top ten aggressive isolates were identified (N-BS24, N-BS7, N-BS28, N-BS36, N-BS27, N-BS37, N-BS15, N-BS38, N-BS19 and N-BS16). Among them, N-BS24 and N-BS28 were able to show high disease against resistant check Chirya 3, so aggressiveness of these two isolates can be further validated through adult plant screening and genetic study and utilize it for resistant breeding program in Nepal.
L. Aryal, S. Shrestha, H. Manandhar et al.· Nepal Agriculture Research J...· 0 citations
Fusarium oxysporum f. sp. cubense (Foc) is a soil-borne fungal pathogen responsible for fusarium wilt, which constitutes one of the major constraints in banana cultivation. Information on the occurrence and molecular characteristics of Foc in Malang Regency, one of the banana-producing areas in East Java, Indonesia, remains limited, hindering effective disease surveillance and management. This study was conducted to isolate and characterize fungal isolates associated with fusarium wilt disease in banana plants using an integrated approach combining morphological characterization, pathogenicity testing, PCR amplification, ITS sequence analysis, and phylogenetic analysis. Three fungal isolates were recovered from symptomatic banana plants collected in Donomulyo, Malang Regency, and one representative isolate (DNM) was selected for molecular characterization based on its morphological similarity to the other isolates. Morphological observations revealed characteristics typical of Fusarium oxysporum. ITS sequence analysis showed 100% query coverage and 100% sequence identity with reference Foc sequences available in GenBank, while phylogenetic analysis clustered the DNM isolate with reference Foc isolates with 94% bootstrap support. Pathogenicity assays demonstrated that the isolate induced typical fusarium wilt symptoms, resulting in an LDI of 16.39% at 14 DAI and an RDI of 41.67% at 45 DAI. These findings provide baseline information on putative Foc isolates in Malang Regency, particularly in the Donomulyo area, and establish an integrated characterization framework to support disease surveillance, early detection, and the development of integrated management strategies for fusarium wilt in banana production systems.
Akhmad Rizal Oktafian, Irisa Trianti, E. Yusnawan et al.· Agro Bali: Agricultural Jour...· 0 citations
Findings establish F. solani as a causal agent of durian stem rot in Hainan and highlight the potential of Bacillus-based biological control as a sustainable strategy for disease management in durian production systems.
