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The influence of leaf age and cultivar on infection of celery by Colletotrichum fioriniae

Stephen Reynolds: University of Guelph

<div>Anthracnose leaf curl, caused by the fungus <em>Colletotrichum fioriniae</em>, is an emerging disease on celery in Ontario, Canada. The objectives of this study were 1) to characterize the early infection process on two celery cultivars, ‘TZ 9779’ and ‘Hadrian’, that differ in susceptibility to leaf curl, and 2) to determine the effect of leaf age on disease development. A conidial suspension (1x10<sup>6</sup> spores mL<sup>-1</sup>) was applied to either the three oldest stalks of 14-week-old plants or immature leaves in the crown. Plants were incubated at 25°C in a greenhouse, and assessed over time. The crown developed lesions 48-72 hour post inoculation (hpi), and had significantly more lesions than mature stalks. Leaf curling was delayed on inoculated mature stalks by 10-15 days. Regardless of cultivar or leaf age, leaf curl symptoms developed on non-inoculated leaves of inoculated plants, suggesting that toxins released by the pathogen can affect other parts of the plant. Disease development did not differ between cultivars. Conidia germination was lower on the immature leaves (41-43%) compared to the mature leaves (64-72%) at 12 hpi, but most conidia have produced melanised appressoria by 96 hpi on either tissue. Quantitative PCR detected the pathogen in asymptomatic mature leaves, with no differences between cultivars. These results demonstrated that immature leaves in the crown are most susceptible to infection, thus chemical control should be directed there.</div>