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Postharvest Pathology and Mycotoxins

Spread of Penicillium digitatum and Penicillium italicum During Contact Between Citrus Fruits. Charles R. Barmore, Plant pathologist, University of Florida, Agricultural Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850; G. Eldon Brown, research scientist III, Florida Department of Citrus, Agricultural Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850. Phytopathology 72:116-120. Accepted for publication 11 May 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-116.

Postharvest infection of healthy citrus fruit by Penicillium digitatum (the cause of green mold) and P. italicum (the cause of blue mold) in contact with decaying fruit was influenced by the amount of aerial mycelium produced on the surface of the lesion at the point of contact with the healthy fruit and the location of the injury-infection site in relation to the contact point. The establishment of infection courts in healthy fruit by both organisms was attributed to injury of healthy rind by an acidic excretion, principally galacturonic acid, from the decay lesions. Treatment of intact fruit rind with spores of either organism contained in a nutrient solution resulted in infection only after the addition of galacturonic acid. P. italicum spread from decaying to healthy fruit more frequently than did P. digitatum when contact between the infected and uninfected fruit resulted from enlargement of the lesion. P. italicum produced sparse aerial mycelium at the contact point, which did not prevent injury of the healthy rind by the excretion. In contrast, P. digitatum produced a thick mat of aerial mycelium at the contact point, which prevented the acidic excretion and thus prevented rind injury and infection. However, when formation of aerial mycelium at the contact point was prevented by the presence of moisture, P. digitatum also spread to healthy fruit. Both organisms spread when the injury-infection site was in contact with the healthy fruit. The exudate from the injury prevented development of aerial mycelia, thus exposing the healthy rind to the injurious acidic excretion.