The composition of pericarp, cell aging, and changes in water absorption in two tomato genotypes: mechanism, factors, and potential role in fruit cracking

Cracking, a serious problem in many fruits, may cause significant economic losses. It may occur when internal pressure cannot sustain by the epidermis any longer. Water absorption and epidermis are among the most important factors that associated with cracking. To determine whether pericarp composition and its mechanical performance, endogenous cell wall disassembly, and water-absorbing capacity influences tomato fruit cracking, we grew a cracking-resistant genotype 'LA1698' and susceptible genotype 'LA2683'. The results illustrated that the cuticle and subcutaneous layer were thicker in 'LA1698' than in 'LA2683'. Compared with 'LA2683', the fruit firmness, consistency, and bursting strength of 'LA1698' were all higher. Fruits of 'LA1698' had decreased activities of polygalacturonase, beta-galactosidase, and cellulose, which can disassemble the polysaccharide network. As a result, it had reduced water-soluble pectin and more covalently and ionically bound pectin that can crosslink with Ca2+ and B. These fruits also have a greater abundance of hemicelluloses. In addition, 'LA1698' had higher SOD activities and lower relative conductivity, meaning its cells might have a better biological activity to resist changes of the external environment (such as water variation) and to prevent fruit cracking. However, POD in 'LA2683' was more abundant than in 'LA1698'. 'LA1698' produced juice with lower total soluble solids, which led to a lower initial water-absorbing ability and difference between the exocarp and mesocarp. In conclusion, a stronger pericarp and cells with a better biological activity in addition to the lower water-absorbing difference between the exocarp and mesocarp made 'LA1698' more resistant to cracking.