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Dispersal of Colletotrichum gloeosporioides by citrus pollen

Sílvia de Afonseca Lourenço: USP

<div><em>Colletotrichum acutatum</em> and <em>C. gloeosporioides</em> are the causal agents of Citrus Postbloom Fruit Drop (PFD). Previous experiments showed that citrus pollen can spread <em>C. acutatum</em>. However, no information concerning <em>C. gloeosporioides </em>is available. The hypothesis is that citrus pollen carried by honeybees can spread the fungus from diseased to healthy citrus flowers. The experiment was performed 3 times in controlled conditions. Flowers from potted sweet orange plants were inoculated with a suspension of 1.25 x10<sup>5</sup><sup>−1</sup> of <em>C. gloeosporioides</em>. The plants were kept for 24 hours under moist chamber at 24°C. Anthers were transferred from inoculated and non-inoculated flowers to healthy flowers. PFD symptoms were evaluated for 3 days. Symptomatic flowers were collected for pathogen isolation on Potato-Dextrose-Agar medium (25 ºC, 12h/12h for 7 days). DNA was extracted from all isolates and PCR assays confirmed the fungal complex species with the specific primers: CgInt/ITS4. All flowers that received anthers inoculated with <em>C. gloeosporioides</em> showed PFD symptoms. All isolates belonged to the <em>C. gloeosporioides </em>complex. None of the flowers that received non-inoculated anthers exhibited PFD symptoms. Images of scanning electron microscopy showed citrus pollen surrounded by conidia of <em>C. gloeosporioides</em> on petals 48 hours after the anther transference. This study confirmed that citrus pollen is able to disperse <em>C. gloeosporioides</em>.</div>