Citrullus lanatus (Thunb.) Matsum. & Nakai - Cucurbit Breeding ...

Abstract
The cultivated watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus] has fruit that
may weigh from 1 kg to over 100 kg. In recent years, preference of consumers has shifted towards fruit of
smaller size than the large types traditionally used for parties and picnics. This trend has produced increased
interest in the genetics of fruit weight, especially among watermelon breeders. The genetics of fruit weight in
watermelon has not been studied widely and there is little published information available to help watermelon
breeders in choosing the proper breeding techniques for working with fruit weight. The objectives of this study
were to determine the inheritance of fruit weight. Six adapted cultivars having the largest and smallest fruit
weight we could find were crossed in a half diallel. We made controlled pollinations to produce F 1, F 2, and BC 1
generations for testing in 2004 at two locations in North Carolina. Generation means and variances were
calculated from single-fruit weights. Giant-fruited parents had higher phenotypic variance than small-fruited
parents. Environmental variance was higher than genetic at Kinston, where the field was less uniform than
Clinton due to poor drainage conditions. At Clinton, genetic and environmental variance were similar for 67%
of the families. Narrow- and broad-sense heritability were low to intermediate and consistent across locations.
In addition, a high number of effective factors was estimated to influence fruit weight in watermelon. Based on
these results, watermelon breeders will have to use quantitative methods to change fruit weight in the
development of new cultivars. Nevertheless, the improvement of qualitative traits in small-fruited germplasm
may be a more successful approach than reduction of the size of large-fruited, high quality cultivars.
Introduction
The fruit of the cultivated watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus] may
vary in weight from 1 kg to over 100 kg. In the United States, commercial fruit are usually classified into four
categories: icebox (14.5 kg) (Maynard, 2001).
The smallest cultivated watermelons are typically produced by 'New Hampshire Midget', from the
University of New Hampshire in 1951. This cultivar has fruit with oval shape, gray rind, red flesh, black seeds,
and thin rind, and produces very early fruit of icebox size (Wehner, 2002). Fruit of smaller size (