You've likely read this before but in case it helps:
QuoteThe interplay between the cuticular biomechanical properties and fruit expansion, in the absence of adequate flexibility, can lead to fracturing of the fruit cuticle and the destruction of the cuticular continuum. In the case of tomato, fruit cracking is also a significant horticultural problem leading to serious economic losses (Bakker, 1988; Peet, 1992; Ehret et al., 1993; Dorais et al., 2004). Cracks have been classified into subcategories of radial, longitudinal, concentric and russeting, or fine cracks, according to the extent, direction and size of the fractures (Peet, 1992). The physiological basis for tomato fruit cracking is unknown, although numerous studies have attempted to shed light on this important phenomenon. Peet (1992) presented seven theories to account for tomato fruit cracking, encompassing both environmental and genetic factors. Unfortunately, the genetic contribution to fruit cuticle cracking is contradictory, and little progress has been made in understanding the genetics of cuticle cracking since Walter (1967) concluded that the inheritance of cracking resistance in the cultivated tomato is 'not simple' and Cuartero et al. (1981) pointed to the low heritability of the trait.
Source: The identification of a gene (Cwp1), silenced during Solanum evolution, which causes cuticle microfissuring and dehydration when expressed in tomato fruit - Ran Hovav et al. - 2017
Also:
QuoteUniform ripening types are associated to some extent with crack resistance and are desirable for paste tomatoes.
Source: How to Breed Tomatoes for Organic Agriculture - Organic Seed Alliance
Table 4 in the paper
Genome Mapping and Molecular Breeding of Tomato - Majid R. Foolad - 2007, on page 22 has 3 entires for fruit cracking QTLs, from Solanum pennellii and Solanum pimpinellifolium.
Among the hypotheses proposed in,
Fruit Cracking in Tomato - M. M. Peet - 1992, is:
QuoteDevelopment of the abscission zone in the tomato pedicel has a role in increasing the susceptibility of the fruit to cracking by progressively restricting water movement out of the fruit.
That makes me wonder if the jointless pedicle trait might help.
That paper also mentions:
QuoteAnother factor may be plant architecture. Shading of the tomato fruit by leaves was thought to account for cracking resistance in at least one cultivar (Frazier, 1952). Presumably, this shading reduces daytime fruit temperatures, which in turn, decreases fruit swelling during the day. Sideshoot pruning (Bakker and Janse, 1988) increases cracking, so cultivars that are vegetatively vigorous may also be more resistant to cracking.
So chasing that trait might help.
For some more recent papers:
Inheritance of Radial Fruit Cracking Resistance in Tomatoes (Solanum lycopersicum L.)
https://iopscience.iop.org/article/10.1088/1755-1315/270/1/012032/meta
LncRNA regulates tomato fruit cracking by coordinating gene expression via a hormone-redox-cell wall network
https://link.springer.com/article/10.1186/s12870-020-02373-9
QTL mapping and candidate genes analysis of irregular fruit cracking in tomato.
https://www.cabidigitallibrary.org/doi/full/10.5555/20210410786
SlGH9-15 regulates tomato fruit cracking with hormonal and abiotic stress responsiveness cis-elements
https://www.sciencedirect.com/science/article/pii/S2095311922002209