What is the difference between long shelf life and firmness?
Can a tomato be firm without having LSL genes?
Is there any relation to green shoulders?
LSL refers to the long shelf life of the tomato fruit, while “Firmness” refers to the attribute of the fruit when harvested. Firmness is a general characteristic of the tomato fruit, while in order to achieve long shelf life in tomatoes we must use specific tomato genes that inhibit fruit ripening. Genes such as NOR or RIN were introduced by classic breeding into commercial tomato varieties from their wild relatives into the mid 80s. These genes can increase shelf life of harvested tomatoes from 6-7 days to over 21 days.
There is no relation between LSL or Firmness and green shoulders. Green shoulders is a different genetic characteristic, caused by a different naturally occurring gene (G), which causes a differential ripening of different parts of the fruit.
There are LSL tomatoes with and without green shoulders, and they can all have different levels of firmness. You just need to pick the right variety.