Cuticular Fractures Promote Postharvest Fruit Rot in Sweet Cherries

Preharvest cuticular fractures in sweet cherry fruit have been suggested to facilitate pathogen invasion, and a method to classify the mount of cuticular fracturing into five categories (from 1 = no visible fractures to 5 = severe fracturing) has previously been proposed. Sweet cherry fruit of the four cultivars Early Burlat, Lapins, Van, and Vista were sorted into these five categories of cuticular fracturing and inoculated with conidial suspensions of either Botrytis cinerea or Monilinia laxa. After incubating the fruit at 20°C and 100% relative humidity for 4 to 7 days, they were assessed for visible fungal growth. Due to quiescent infections of M. laxa, fruit treated with B. cinerea developed more brown rot than gray mold. However, a significant linear relation (P < 0.05) between the amount of cuticular fracturing and fungal infections was obtained in five of seven trials with B. cinerea and in two of four trials with M. laxa, indicating that fungal infections in sweet cherry fruit may be facilitated by cuticular fractures. Independent of cultivar and year, a significant linear relation was found between the category of cuticular fracturing and percentage of infected fruit after inoculation with both B. cinerea and M. laxa, and in control fruit (P = 0.0001, 0.0183, and 0.0182, respectively). This is the first report quantifying an increase in fungal infection with increasing amount of cuticular fracturing. The mean difference in fruit rot (%) ± standard deviation among fruit in fracturing categories 1 and 5, expressed as the linear contrast of amount of fruit rot in category 5 minus amount of fruit rot in category 1, was 37.2 ± 7.4 (P = 0.0001), 35.4 ± 11.0 (P = 0.0022), 17.0 ± 6.7 (P = 0.0135), and 29.8 ± 4.7 (P = 0.0001), after treatments with B. cinerea, M. laxa, water control, and for all data pooled, respectively.