During the first four months of 2000, mature fruit of clementine cvs. Clemenules and Hernandina, mandarin cvs. Ortanique and Fortune, and orange cv. Navelina from several packinghouses located in Valencia Province were affected by a soft, watery, colorless or very light brown decay. The incidence of the decay was 5 to 12% in clementines and mandarins and 0.2 to 0.8% in oranges. A yeast was isolated consistently on potato-dextrose agar from affected tissues and from the juice of decayed fruits. Colonies of this yeast were butyrous, light cream in color, and smooth with a dry surface (or with a flattened center) and lobed margins with sparse, branched pseudohyphae. Some isolates that were light pink in color later turned cream colored. Yeast cells were ovoid to elongate, single or in pairs, with one or two buds at one end (multilateral budding). The cells were 1.1 to 5.7 μm × 3.2 to 12.8 μm. Ascospores were not observed. Fermentation and growth on carbon sources (several carbohydrates), growth on nitrogen sources (nitrate, cadaverine, L-lysine, etc.), requirement for vitamins, and growth at 40°C were used for identification. Based on the results of such tests and morphological characteristics, the fungus was identified as Issatchenkia orientalis Kudryavtsev (anamorph: Candida krusei (Castellani) Berkhout) (2). To satisfy Koch's postulates in pathogenicity tests, cells from pure cultures on agar or in orange juice were inoculated by hypodermic injection into the peel and flesh of oranges, clementines, mandarins, grapefruits, and lemons. After 10 to 20 days in a moist chamber at 24°C, a decay resembling symptoms that occurred in the packinghouse were observed in the inoculated fruits (1,3). The lemon fruits were the most affected. The fungus reisolated from decayed fruits was identical to the original isolates. This is the first report of this yeast as a decay of citrus produced in Europe. Climatic conditions (rainfall in spring and dry in summer and autumn) in citrus-growing areas in Spain, together with the presence of the Mediterranean fruit fly, may have been factors in disease development. A similar decay is caused by Geotrichum candidum, and previously this may have been mistaken for decay caused by I. orientalis.
References: (1) P. R. Harding. Plant Dis. Rep. 52:433, 1968. (2) C. D. Kurtzman. 1998. The Yeasts, A Taxonomic Study. 4th ed. Elsevier Science, Amsterdam. (3) K. V. Shankhapal and V. G. Hatwalne. Plant Dis. Rep. 60:237, 1976.