The plant may be kept "small" by pinching etc.... start with a patio (determinate type) tomato....
There are also chenicals that will shorten the internode spacing resulting in a "smaller" plant.

i have no background to give you the science...

but my gut says that a rooted cutting of a plant... IS EXACTLY THE SAME PLANT.... there can be no genetic degradation in any sense ...

so how can 4 subsequent cuttings off off 3 subsequent generations have lost some genetic vigor????

maybe they should try growing them in a new location ... perhaps the problem is related to growing tomatoes in the same location for multiple generations.. in other words.. lack of crop rotation ... that guess is as possible as the other..

but as i said.. its just gut comments.....

good luck

ken

That's what I was thinking also.
A cutting should look exactly like the parent.
I've search the net but could not find any info on cuttings resulting in smaller plants.
I started some cutting with an indeterminate brandywine tomato.
I guess I will see the results by March.

no ...

i know it might be hard.. but try to wrap your head around this:

IT IS THE SAME PLANT ....

not as you say 'looks like the same plant' ...

if you root a piece... how can it be any different????

if you grew the seeds from a given plant .... it would be a 'cross' between the mother and father plant... and even if it did look the same .... it probably isn't ...

do you see the difference?

of course this is leaving out happenstance genetic mutation of branches which might inadvertently be selected for rooting ... i don't know if tomato does that though ...

ken