Interrelationship between the characteristics of fruit growth and the cracking susceptibility in apple and sweet cherry cultivars

Several characteristics of fruit growth, i. e., the ratio between the daily mean rate of change in cross or polar diameter to their final diameters (DRC or DRP) were measured in 15 apple and 8 cherry cultivars, and analyzed with respect to their correlations to the several indices of susceptibility of fruit cracking, the physical properties of the peels and the distribution of invisible fine cracks. 1. In apple cultivars, the 4 indices of the susceptibility were : cracking index (CI), mean density of ring fracture (MDR), mean density of lengthwise fracture (MDL) and MDR + MDL. These indices correlated positively to the ratio between the daily rate of change in cross diameter, measured about 30 days after full bloom, to the final diameter (DRC(1)). Furthermore, the same indices correlated positively to the difference between the ratio in the transverse direction and that in the polar direction (DRC-DRP) and the degree of irregularity in the fruit growth, i. e., their standard deviation from the mean ratio or their standard error from the estimated ratio (DRP(sd) or DRC(se) and DRP(se)). 2. In cherry cultivars, the mean densities (number) of lengthwise fractures on the fruit surface per centimeter (MDL) were highly and positively correlated to DRC at the beginning of the III stage of the fruit growth and also to DRC-DRP at the same time. 3. The shearing stress of the apple peels correlated negatively to mean DRC, mean DRP and DRC(sd). And the many values relative to DRC, DRP, DRC-DRP and their standard deviation correlated positively to the elongation length of the peels in the direction of the longitudinal are in both species. 4. These strains and irregular thickenings may increase fine and invisible cracks in both species.