Molecular Variability of Causal Agents of Twister Disease of Onion (original) (raw)
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Abstract Leaf Twister disease (LTD) is a major disease of onion (Allium ascalonicum L.) cultivated in Sri Lanka. The present study was aimed to determine molecular and pathogenic variations among the causal agents of onion leaf twister disease. The pathogens causing the LTD have been identified as Colletotrichum and Fusarium spp. Pathogenic variations of the fungal isolates, in terms of pathogenicity and virulence were determined in vivo by inoculation assays using red onion (variety Vethalan). LTD-infected plants were collected from farmer fields of four locations of Batticaloa district, Sri Lanka. Possible causal organism/s of LTD were isolated from three different parts of the infected plants, namely leaves, pseudostem and bulb. Morphologically-different six isolates of Colletotrichum and seven Fusarium isolates were obtained by isolations. Virulence of the Colletotrichum and Fusarium varied significantly among the isolates in terms of rapidity and extent of disease spread. Variety Vethalan was not completely resistant to any isolate of the two fungal genera tested. Genomic DNA of 13 isolates was extracted from each purified isolate using a modified CTAB method. PCR amplification was done with ITS1 and ITS4 primers to amplify the 5.8S-ITS subunit of the Colletotrichum isolates. The ITS2-rDNA subunit of Fusarium isolates was amplified by ITS-Fu1f and ITS-Fu1r primers. As expected 590 bp and 466 bp PCR products were resulted in by all Colletotrichum and Fusarium isolates, respectively. Colletotrichum isolates showed two polymorphic groups based on PCR-RFLP by RsaI, Hae III and Msp I. Fusarium isolates showed no polymorphism based on PCR-RFLP by Rsa I, Hae III and Msp I. Findings of the present study revealed that molecular and pathogenic variations exist among different isolates of Colletotrichum and pathogenic variations only exist among Fusarium isolates infecting red onion in Batticaloa district of Sri Lanka.
ABSTRACT: Leaf Twister Disease (LTD) is one of the major biotic constraints of onion cultivation in Sri Lanka. The present study was conducted to determine morphological and pathogenic variations among Colletotrichum and Fusarium isolates, causing LTD. Fungal isolates were obtained from LTD-infected onions, collected from 30 locations in the Jaffna district of Sri Lanka. The colony characters, spore dimension, colony growth rate and fungicide sensitivity in vitro and in vivo were used to determine the morphological variations of fungal isolates. Pathogenic variations of the fungal isolates in terms of pathogenicity and virulence were determined by in vivo inoculation assays using red onion (Allium cepa L.) variety Vethalan. Morphologically-different 29 isolates of Colletotrichum and 16 isolates of Fusarium were collected from different farmer fields of Jaffna district. Out of the 29 Colletotrichum isolates, six were identified as C. gloeosporioides by morphological features of fungal colonies and spores. Colony and spore morphology also resembled C. acutatum and C. fragaria among the Colletotrichum isolates associated with the LTD infections of onion. Colony growth rate and in vivo sensitivity to fungicide (Thiophanate-methyl 50% + Thiram 30% WP) were highly variable among the tested isolates of Colletotrichum and Fusarium. Recommended dosage of the fungicide completely inhibited the mycelia growth in vitro. However, the recommended dosage as only a single seed treatment did not completely control any isolate of Colletotrichum or Fusarium under in vivo conditions. Virulence of the Colletotrichum and Fusarium varied significantly among the isolates in terms of rapidity and extent of disease spread. The red onion variety Vethalan was not completely resistant against any isolate of the two fungal genera tested. The present study revealed that the morphological and pathogenic variations exist among different isolates of Colletotrichum and Fusarium causing LTD in red onion in Jaffna district of Sri Lanka. Keywords: Colletotrichum spp., fusarium spp., leaf twister disease, colony and spore morphology, red onion
Anthracnose of Onion (Allium cepa L.): A Twister Disease
Pathogens
The onion (Allium cepa L.) is a lucrative and high-value vegetable–spice crop in India, but it is sensitive to several of diseases caused by fungi, bacteria, viruses, and nematodes, of which a fungal disease, anthracnose, caused by Colletotrichum spp., is a major issue for both onion producers and researchers since it severely affects the bulb production. Twister disease is currently one of the most common problems in onion production, particularly in humid regions, and it reduces productivity while also lowering the value and profitability. Twister disease is visualised by white or pale-yellow water-soaked oval depressed lesions on leaf blades, which are the first symptoms. Lesions expand as the disease advances, and numerous black-coloured, slightly elevated structures/fruiting bodies appear in the middle area, arranged in concentric rings. Curling, twisting, chlorosis of the leaves, and aberrant extension of the neck or pseudo-stem occurs, followed by rotting of the bulb. In an u...
Colletotrichum species responsible for severe outbreaks of anthracnose on onion in southwest India are reported. These fungi produced white, oval sunken lesions on the leaves and neck at the onset of infection followed by appearance of necrotic centres with grey-colored concentric rings of acervuli, which eventually covered the whole leaves and subsequently led to collapse of the plant. Thirty seven isolates of Colletotrichum recovered from diseased leaves and neck were characterized based on morphological characteristics and partial sequences of ACT, TUB2, CHS-1, CAL, CYLH3, GAPDH, GS and ITS genes. The combined multilocus sequence analysis coupled with a critical examination of the phenotypic characters revealed the presence of two species, Colletotrichum siamense (27 isolates) and Colletotrichum truncatum (10 isolates). Pathogenicity of both species was ascertained on onion seedlings of cv. Arka kalyan. To our knowledge, this is the first report of C. siamense and C. truncatum causing anthracnose disease on onion.
Zbornik Matice srpske za prirodne nauke, 2017
Onion (Allium cepa L.) is one of the most important vegetable crops in Serbia, where it is grown on an approximate surface of 20,000 ha. During the routine quality control analysis of onion seed in 2014, fungal infection was observed in an average of 28% of the seed. The objective of this paper was to isolate, determine, and identify Fusarium sp. based on the pathogen?s morphological and molecular characteristics. Onion seed samples were collected from different localities in the region of Vojvodina. To obtain a DNA se?quence-based identification, a total DNA of the 25 isolates was extracted directly from the mycelium (~ 100 mg wet weight), with a DNeasy Plant Mini Kit (Qiagen, Hilden, Germany). Following DNA extraction, the translation elongation factor 1-alpha region was amplified by PCR with the primer pair EF1 and EF2. An amplicon of 700 bp was amplified in 25 tested isolates. Identification of one isolate was performed by sequencing the translation elongation factor EF-1? gene,...
World Applied Sciences Journal
The queen of kitchen Allium cepa L. cultivation is catastrophic by devastating fungal pathogens in Jaffna, Sri Lanka. A field investigation was carried out to diagnose the fungal diseases of red onion and to provide possible alternative for hazardous fungicides. Fusarium oxysporum f. sp. cepae was isolated and characterized by cottony and irregular concentric shaped white colony, later turned to creamy non smooth and hyaline mycelium. Disease symptoms were identified as yellowing, curling and necrosis at the tip of leaf blades. With time, whole leaf blades showed symptoms and eventually wither and decay. Colletotrichum gloeosporioides produced greyish white to dark gray, circular cottony appearance and produce irregular concentric rings on PDA medium. Disease symptoms of leaf twister are identified as appearance of leaf curling, twisting, chlorosis and abnormal elongation of the pseudo stem. In the field experiment, Trichoderma viride, Neem leaf extract, Distillery spent wash were t...