Relationship between the Occurrence of Hollowing in Watermelon and the Size and the Number of Fruit Cells and Intercellular Air Spaces.

Abstract

Hollowing (formation of a central cavity) in watermelons plagues the growers by reducing their market values. This paper reports the relationship between the occurrence of this disorder and fruit weight, cell size and number, and the volume of the intercellualr air spaces as by a) nodal position of the fruit, b) NAA application, and c) partial defoliation of the bearing.Fruits borne on the lower, basal nodes (Treatment L) were lighter at harvest than those borne on higher, distal nodes (Treatment H) but the former trended to develop hollowing, whereas the latter did not exhibit this physiological disorder. The basal fruits had fewer but larger cells through the transverse diameter than those of distal fruits ; they also had larger intercellular air spaces than the distal melons did. Fruits painted with NAA (Treatment N) and those on partially defoliated shoots (Treatment D) produced smaller melons having a small or no hollowing. Compared to the basal melons, the NAA- treated ones and those on defoliated shoots had proportionately less large cells and smaller intercellular air spaces.From these results, the following assumptions are drawn. The growth of cells in the inner region of basal fruits with its lower cell density cannot keep pace with the growth of the peripheral cells and of the rind having higher cell density. This differential growth causes cleavage to arise in the inner part of the fruit which gradually develops into a hollowing. When the growth of the fruit is suppressed by NAA or by defoliation, the cells in the inner region are able to grow as fast as those in and near the rind so that no stress is generated within the fruit. Conversely, when the number of cells per fruit is large, as it is in fruits on distal nodes, the growth of cells of the inner region keeps pace with that of the rind. Consequently, no internal strain ensues and no cavitation occurs.