What causes the crease through the pericarp of a drupe fruit (peach, nectarine, olive)? It may just be in exocarp as @Ilan pointed out, but I assumed (perhaps wrongly), that the division continued through the pericarp. I'm also not sure if this true generically for drupe fruit, so I'm not sure which phylogenetic step down to take. Olives for example have a divot that seems to extend from the stem down, but it stops well before the midline of the fruit in most cases.
I assume the crease has something to the initial genesis of the fruit tissue, but I haven't found any arguments on it's formation. A more technical term might be "cleavage," but that was after some searching and not coming up with more certain term.
Botany is not my strong suite, but I recently entered into a collaboration where we will be making some recombinant alpha viruses (which is within my strong suite) that will infect drupe tissue. Finding good pathology papers has been difficult, and they tend to be specific (not trying to imply that's bad). Can anyone point towards a reference text/article on the genius of drupe fruit if the cause of the "crease" is not clear? Disruption of the crease seems to be a particular phenotype of infection for some strains, and I'm searching for the correct terminology and mechanisms that might be effected.
If I can get permission I will include photos of an infected vs control peach. In the mean time to clarify what I mean, the line that seems to transverse from one poll to the other of the fruit:
On the sea mango it is pronounced, but on most other mango it seems like just a slight marking along the exocarp:
Even the coconut seems to have at least one: