Any of a number of species including Pythium, Phytophtora, Rhizoctonia, and Alternaria
Numerous fungi cause fruit rots on tomato. Lesions may be superficial, or black or brown sunken areas that extend into the internal fruit tissue. Lesions often occur near the stem end scar.
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.