Damage???

[Garf]

I believe this is genetic rather than insect damage.

[img]https://www.mastercontrollinelinksite.info/Gardening/defect.jpg[/img]

[sepeters]

I can see why you'd think it would be genetic; many of the larger heirloom and beefsteak tomatoes have what looks like little pockets around the blossom end, which can be normal. I have never seen them develop on the side, but I have definitely seen my tomatoes split on the side before. To me it looks like your tomato split on the sunny side, probably from a combination of higher temps and inconsistent watering or just plain inconsistent watering. Tomatoes are famous for this and some varieties are very finicky about their drinking habits. Try to establish a set watering schedule that never allows your plants to completely dry out and don't deviate from it if possible.
Is it just the one tomato? The whole plant? Or all the tomatoes in your garden?

[sepeters]

Unless it is a sungold or sungold hybrid. Looks too big for that though.

[Garf]

It was not Sungold.

[imafan26]

It looks like mild catfacing.
https://learningstore.uwex.edu/assets/pdfs/A3111.PDF

[applestar]

Looks to me like incomplete zippering, which if I remember correctly occurs from defective pollination and dragging of of something to something inside the blossom. (sorry, pre-coffeee.....)

[imafan26]

Zippering does not usually cause the fruit to form irregular lobes. Zippering is supposedly caused by the anther getting stuck on the developing fruit causing a scar. The scar is usually thin and long. Holes can happen but they are usually small.

Catfacing holes are near the blossom end as it shows in the picture and causes irregular bumps in the fruit. The right side of the fruit is lobed, not smooth. The hole usually is filled with scar tissue.

Most likely the cause can be physiologic or environmental and can have a genetic component as well.

https://edis.ifas.ufl.edu/hs200

[hendi_alex]

Bottom line for me, the tomato will usually form a tasty mature fruit in spite of such superficial defects.