Passing along helpful information that Suze gave me today (thanks, Suze!) You may want to check these links and do a search for botrytis to see if it looks similar. It can cover the bottom of the stem and look dark and fuzzy/powdery.
If you think it is botrytis, I would encourage you to look through the following:
http://vegetablemdonline.ppath.corne...o_Botrytis.htm
http://aggie-horticulture.tamu.edu/t.../handbook.html
Gray Mold (fungus - Botrytis cinerea): Plants become more susceptible to this disease as they become older. It is mostly a problem in greenhouses, but it can also affect tomatoes in the field. The fungus first becomes established on dead leaves at the base of the plants. A heavy, gray growth of the fungus covers these, and numerous spores are soon found, giving the affected area a cottony appearance. Affected leaves collapse and shrink. The fungus progresses into the stem, producing cankers. Affected fruits first show a watersoaked, soft area in the points of infection. The dark gray growth of the fungus soon is seen on these spots. Regular fungicide applications should help in controlling this disease.
Botryosporium Mold (fungus - Botryosporium sp.): This fungus can often be found on greenhouse tomatoes. It superficially resembles gray mold.