> Modern vegetables are, in general, less bitter than in earlier times.
That does not necessarily mean more sugar - it just means less bitter. (These axes are independent).
Selective breeding puts pressure on easy-to-grow-and-sell (shelf life, size, shape, resistance to pests) and only afterwards on flavor.
And another important (and often forgotten) point about modern frutis and vegetables is that they are mostly picked when green (when not all sugar has ripened yet), and then chemically ripened in a process that does not yield as much sugar as natural ripening.
I would like a reference before I believe that today's fruits and vegetable contain more sugar than those of 50 years ago.
Oh, sure, wasn't meant as a reference, but just some evidence that it's not totally implausible.
Selective breeding, of course. Modern vegetables are, in general, less bitter than in earlier times. Fruits are often sweeter---and easier to farm industrially and bring to market. Also, we live off less different kinds of fruit and vegetables than in earlier times. There used to be hundreds of different apples in widespread use for examples.
Not saying that it's necessarily bad. Just that pron's hypothetical argument isn't actually all that hypothetical.