Differing rind characteristics of developing fruits of smooth and netted melons (Cucumis melo)

The suberized net tissue of the rind of muskmelon (Cucumis melo L.) is of agricultural importance as an indicator of fruit maturity and quality, and as a preventive factor against mechanical injury, both pre- and postharvest. The net originates from cracks that appear at the surface of the fruit. Therefore, a comparative study was conducted with two netted-rind and two smooth-rind melon varieties, to identify fruit characteristics associated with initiation of netting development. The developmental pattern of fruit expansion did not differ between smooth and netted melon varieties. Rather, our results indicated that inherited cuticular/epidermal characteristics are probably associated with the development of fissures in the fruit rind. The rind of the netted fruit was found to contain significantly more cuticle than that of the smooth-rind variety during the period of maximal growth rate; moreover, in the rind of the smooth varieties the deposition of the cuticle was mainly on the outside of the epidermal cells, while in the case of the netted varieties it enclosed most of the cells. These cuticular characteristics of the netted varieties may reduce the elasticity of the rind during the dramatic expansion phase of the fruit, and so make it more susceptible to cracking and suberization. Further, the configuration of flattened epidermal cells in the netted rind allowed less surface contact between adjacent cells and fewer cells per unit area of fruit surface, than the narrow and elongated epidermal cells found in the smooth-rind fruit. These epidermal characteristics of the netted varieties may contribute to the weakness of the epidermal layer in resisting the tensile forces imposed by the internal pressure of the growing fruit.