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Factors Affecting the Occurrence and Severity of Blackmold of Ripe Tomato Fruit Caused by Alternaria alternata. R. C. Pearson, Graduate Student, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: New York State Agricultural Experiment Station, Hudson Valley Lab., Highland, N. Y. 12528; D. H. Hall, Extension Plant Pathologist, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 65:1352-1359. Accepted for publication 23 June 1975. DOI: 10.1094/Phyto-65-1352.

Free moisture as dew deposition was essential for rapid germination of conidia in the absence of rainfall. Dew was deposited at ambient temperatures at or below 15 C, temperatures that were suboptimal for rapid germination of conidia. However, water soluble nutrients; e.g., glucose and fructose, on the fruit surface dissolved in the dew, stimulated germination of conidia at 6-15 C. Infection and symptom development were enhanced by prior exposure of fruit to ultraviolet (UV) and infrared radiation under field conditions, but they were not required for disease development under greenhouse conditions. Inoculation of ripe fruits frequently resulted in large, sunken lesions whereas inoculations of green fruit resulted in quiescent lesions that failed to enlarge after the fruit ripened. Sporulation was optimum at 27 C and was inhibited below 15 C and above 33 C. Extended periods of temperature at 15 C or below reduced numbers of conidia trapped in late September and October. Conidia were liberated in a diurnal pattern under field conditions, and maximum release occurred from 1200 to 1800 hours.

Additional keywords: fruit exudates, dew, epidemiology.