Any of a number of species including Pythium, Phytophtora, Rhizoctonia, and Alternaria
Numerous fungi cause fruit rots on tomato. Large areas of the fruit appear water-soaked, with off color darker or lighter patches. Fruit may appear intact until touched. Handling usually punctures skin and internal watery tissue escapes.
Fruit should be kept off the soil (if possible), and surface wetting should be minimized. Furrow or drip irrigation is preferred over sprinkler irrigation. Preventative fungicide sprays may be required if a “zero tolerance” for defects production system is needed.