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First Report of Fusarium oxysporum Causing a Leaf Twisting Disease on Allium cepa var. ascalonicum in Sri Lanka

Plant Disease (Impact Factor: 3.02). 07/1999; 83(7):695-695. DOI: 10.1094/PDIS.1999.83.7.695C
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    • "Identification of Colletotrichum and Fusarium isolates was based on morphological characters such as colony characters and size and shape of conidia according to descriptions of Simmonds (1965), Smith and Black (1990) and Sutton (1992). Among the isolated fungal cultures, identification was focused on Colletotrichum and Fusarium species as C. gloeosporioides and F. oxysporum have been identified as the causal organisms of LTD (Weerarathne, 1997; Kuruppu, 1999). It is interesting to note that 70% of the Fusarium isolates were obtained from infected onion bulbs and 76% of the Colletotrichum isolates were obtained from infected leaves. "

    Full-text · Article · Oct 2015
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    • "A disorder called " Leaf twister disease " (LTD) / disco disease has been reported since 1970 as a severe threat to bulb and seed crop production of onion. Colletotrichum gloeosporioides and Fusarium oxysporum have been identified as the predominant microorganisms associated with the LTD-infected onion tissues based on morphological analyses (Weeraratne, 1997; Kuruppu, 1999). Lower part of the leaves of LTD-infected plants develop sunken pale patches which later turn into grayish coloured lesions. "
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    ABSTRACT: 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.
    Full-text · Article · Jan 2014
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    • "Identification of Colletotrichum and Fusarium isolates was based on morphological characters such as colony characters and size and shape of conidia according to descriptions of Simmonds (1965), Smith and Black (1990) and Sutton (1992). Among the isolated fungal cultures, identification was focused on Colletotrichum and Fusarium species as C. gloeosporioides and F. oxysporum have been identified as the causal organisms of LTD (Weerarathne, 1997; Kuruppu, 1999). It is interesting to note that 70% of the Fusarium isolates were obtained from infected onion bulbs and 76% of the Colletotrichum isolates were obtained from infected leaves. "
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    ABSTRACT: 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
    Full-text · Article · Jan 2014
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