I observe a phenomenon for many years now. I observe it on a wide diversity of tomatoes produced all over Europe and Northern Africa that are sold at my local supermarket.
When I keep my tomatoes at ambient temperature around 20 to 25 degrees celsius, they deteriorate after a variable time, usually starting a five to fifteen days after I bought them. Nothing abnormal so far.
However, I observed that the mold pattern of virtually all these tomatoes is the same. It almost always starts a few millimeters from the junction where the tomato was attached to its branch, forming a ring on the top of the fruit.
I have thought why this could happen and my main hypothesis is that when they are grown the sun hits the top of the tomatoes (except where it is attached to the branch, obviously) and some ultraviolet radiation might weaken the tomato resistance in some way. The other reasonable hypothesis, although I cannot think of a definite mechanism, is that gravity would favor this polarized degradation. I have other hypotheses but they are too far a stretch, I believe.
So what is really happening?
I am a biologist, just not into botany or agriculture, so feel free to go technical and not just oversimplify.