Investigations on “natural” cuticular cracks were conducted on nectarine fruit [Prunus persica (L.) Batsch var. nucipersica (Suckow) C.K. Schneid.]. A method for quantifying the cuticular crack surface area on a whole fruit basis was proposed. By using a stratified sampling design, the spatial distribution of the cuticular cracks over three regions (stylar end, peduncle, and cheek), their morphology, and the estimation of the total proportion of cuticular cracks on the fruit were studied. These features were examined during fruit development and in response to several fruit growing conditions corresponding to various crop loads and irrigation regimes. Cuticular cracks on nectarine fruit occurred during the final rapid fruit growth stage. Larger fruit presented higher cuticular crack densities in the apical regions than in the cheek regions. Thin and larger cuticular cracks occurred continuously during fruit development. Cuticular cracks represented 10% to 12.5% of the fruit surface area for well irrigated or low crop load trees, whereas they covered less than 4.5% for the heavy crop load and water deficit treatments. Cheek regions largely contributed to the total cuticular crack surface area (>60%), regardless of the fruit growing conditions. After irrigation was restricted, cuticular crack development was limited. A positive relationship was established between the cuticular crack surface area per fruit surface area and the fruit fresh weight.

By predicting crack occurrence during fruit growth, this model could be helpful in managing cropping practices for integrated plant protection.

This study describes the components of fruit surface conductance. It aims to revise a modelling framework examining water loss across the fruit epidermis in relation to time and fruit growing conditions. For this purpose, cuticular crack surface area, healing artificial wounds in vivo, stomatal number and total fruit surface conductance were quantified during nectarine (Prunus persica L. nucipersica) fruit growth under contrasted irrigation regimes or thinning intensities. The contribution of stomatal component to total conductance decreased very early. A sub-model of the specific cuticular conductance according to fruit age was proposed that accounted for the complex temporal variation of the cuticular component. The occurrence of cracks was modelled by considering the relative expansion rate of the cuticle as a function of fruit fresh mass and relative expansion rate of the fruit. Healing decreased with fruit age. The observed temporal variations of fruit surface conductance and cuticular crack surface area were well simulated by the modified model whatever the fruit growing conditions. Tests on independent data revealed that the model was highly sensitive to parameters related to cuticular crack development and to cuticular properties.

The effects of cuticular crack surface area and inoculum density on the infection of nectarine fruits by conidia of Monilinia laxa were studied using artificial inoculations with conidial suspensions and dry airborne conidia during the 2004 and 2005 seasons, respectively. Additionally, the effect of ambient humidity on fruit infection was evaluated in the 2005 experiment. An exploratory analysis indicated that (i) ambient humidity did not significantly explain the observed variability of data, but that (ii) the incidence of fruit infection increased both with increasing inoculum density and increasing surface area of cuticular cracks. The product of these two variables represented the inoculum dose in the cracks, and was used as a predictor of fruit infection in the model. Natural infection in the orchard was observed to increase throughout the season in both 2004 and 2005. The relationship between the probability of fruit infection by M. laxa and the artificially inoculated dose in the cuticular cracks was well described by a logistic regression model once natural inoculum density was taken into account (pseudo R 2 = 65%). This function could be helpful for estimating the risk of fruit infection at harvest based on fruit size and natural inoculum density.

No abstract