Abstract
Fusarium oxysporum is a globally distributed soilborne fungal pathogen causing root rots, bulb rots, crown rots and vascular wilts on a range of horticultural plants. Pathogenic F. oxysporum isolates are highly host specific and are classified as formae speciales. Narcissus is an important ornamental crop and both the quality and yield of flowers and bulbs can be severely affected by a basal rot caused by F. oxysporum f. sp. narcissi (FON); 154 Fusarium isolates were obtained from different locations and Narcissus cultivars in the United Kingdom, representing a valuable resource. A subset of 30 F. oxysporum isolates were all found to be pathogenic and were therefore identified as FON. Molecular characterisation of isolates through sequencing of three housekeeping genes, suggested a monophyletic origin with little divergence. PCR detection of 14 Secreted in Xylem (SIX) genes, previously shown to be associated with pathogenicity in other F. oxysporum f. spp., revealed different complements of SIX7, SIX9, SIX10, SIX12 and SIX13 within FON isolates which may suggest a race structure. SIX gene sequences were unique to FON and SIX10 was present in all isolates, allowing for molecular identification of FON for the first time. The genome of a highly pathogenic isolate was sequenced and lineage specific (LS) regions identified which harboured putative effectors including the SIX genes. Real-time RT-PCR, showed that SIX genes and selected putative effectors were expressed in planta with many significantly upregulated during infection. This is the first study to characterise molecular variation in FON and provide an analysis of the FON genome. Identification of expressed genes potentially associated with virulence provides the basis for future functional studies and new targets for molecular diagnostics.
Highlights
Fusarium oxysporum is a globally important plant pathogen, causing root rots, bulb rots, crown rots and vascular wilts on a wide range of horticultural crops and ornamental plants including onion, lettuce, tomato, cucumber, pea, daffodil (Narcissus), carnation, lily, tulips and Gladiolus (Leslie and Summerell, 2006; Michielse and Rep, 2009)
Fusarium was consistently isolated from Narcissus bulbs samples with typical basal rot symptoms obtained from different locations and cultivars in the United Kingdom and the collection of over 150 isolates represents a valuable resource
The 30 isolates selected on the basis of culture morphology and origin were all identified as F. oxysporum and as they were all pathogenic on Narcissus bulbs were designated as FON
Summary
Fusarium oxysporum is a globally important plant pathogen, causing root rots, bulb rots, crown rots and vascular wilts on a wide range of horticultural crops and ornamental plants including onion, lettuce, tomato, cucumber, pea, daffodil (Narcissus), carnation, lily, tulips and Gladiolus (Leslie and Summerell, 2006; Michielse and Rep, 2009). Pathogenic F. oxysporum isolates are highly host specific and are classified as formae speciales (Leslie and Summerell, 2006; Michielse and Rep, 2009). Members of nine transcription factor families on FOL LS regions (TF1-9) have roles in virulence through controlling effector gene expression (van der Does et al, 2016). Phaseoli, causing wilt of common bean, revealed that Fusarium transcription factor (FTF1) from the TF1 gene family, plays a role in virulence through controlling the expression of at least two SIX genes (Nino-Sanchez et al, 2016) Research investigating F. oxysporum f. sp. phaseoli, causing wilt of common bean, revealed that Fusarium transcription factor (FTF1) from the TF1 gene family, plays a role in virulence through controlling the expression of at least two SIX genes (Nino-Sanchez et al, 2016)
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