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Postharvest Pathology and Mycotoxins

Synergism of Geotrichum candidum and Penicillium digitatum in Infected Citrus Fruit. S. C. Morris, Gosford Horticultural Postharvest Laboratory, New South Wales Department of Agriculture, P.O. Box 355, Gosford, N.S.W. Australia 2250; Phytopathology 72:1336-1339. Accepted for publication 8 February 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1336.

Consistently high levels of sour rot of citrus fruit by Geotrichum candidum were obtained by adding Penicillium digitatum spores to the inoculum and incubating the fruits at high relative humidities and at either 30 or 25 C after dipping them in benomyl. Synergism was greatest in mature fruit and occurred over a wide range of spore concentrations of G. candidum and P. digitatum. The ability of spores of G. candidum to induce disease was particularly increased by adding nutrients to the inoculum. The spores, rather than the sterile filtrate of a P. digitatum spore suspension, were found necessary for synergism to be expressed. Benomyl prevented development of symptoms caused by P. digitatum, but not spore germination and therefore permitted the synergistic increase of G. candidum to occur. Therefore, fungicides that prevent germination of P. digitatum spores should markedly reduce sour rot losses due to G. candidum.