Influences of Epidermal Cell Sizes and Flesh Firmness on Cracking Susceptibility in Sweet Cherry (Prunus avium L.) Cultivars and Selections.

Abstract

Susceptibility of cherry cultivars using water immersion method was investigated to determine the degree and rate of cracking, water absorption rate, fruit weight, flesh firmness, vertical and lateral lengths of the epidermal cells at the fruit apex, cheek, stalk cavity and suture. Thirty nine samples consisting of 37 sweet cherries, one sour cherry and one hybrid between sour cherry and Prunus pennsylvanica were used. The degree and rate of cracked fruit increased with time after immersion varied among cultivars : 'Turkey Black Heart', 'Jumbonishiki, ' 'Okitama-6, ' 'Ebony, ' 'Venus' and 'Valera' were small, whereas 'Napoleon, ' 'Van, ' 'Compact Lambert' and 'Vic' were high. A huge variance occurred among cultivars with respect to fruit weight, flesh firmness, and vertical and lateral lengths of skin cells. After 12 hours of immersion, the following significant positive correlation coefficients were established between degree of cracking and fruit weight, flesh firmness, vertical and lateral lengths of skin cells at apex respectively ; 0.664, 0.515, 0.649 and 0.515. Likewise, the rate of cracked fruit had significant positive correlations with fruit weight, flesh firmness, vertical and lateral lengths of skin cells at apex, respectively ; 0.718, 0.503, 0.763 and 0.669. Thus, cracking susceptibility is strongly related to fruit weight, flesh firmness and skin cell size, especially at the fruit apex. Significant positive relationships were also obtained between the water absorption rate, and flesh firmness and vertical length of the skin cells of the fruit apex. The contribution rates of cracked fruit rate and degree of cracking to all other parameters were 78.8 and 69.0%, respectively. Likewise, high contribution rates of 70.7 and 57.3% were obtained between fruit weight and flesh firmness to vertical length of the fruit apex. Hence, the possibility of estimating cracking susceptibility based on these three parameters is considered. Having obtained significantly high yearly correlation coefficients of 0.885, 0.880, 0.706 between degree of cracking, rate of cracked fruit and water absorption rate using 28 cultivars over a 2-year period, the water immersion method to determine the degree of cracking was validated.