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

Breeding Methods
Traits of interest to commercial watermelon breeders are disease resistance, yield, fruit size, and
nutritional content (sugars, lycopene, etc.). The breeding techniques adopted for the improvement of these traits
are limited to pedigree and backcross breeding. Even though these breeding schemes are useful to transfer
single genes to high quality cultivars, they do not necessarily suit the requirements for the improvement of
quantitative traits, such as yield, nutritional content, and resistance to certain diseases.
The development and release of recombinant populations for population improvement and inbred
development is a major need to ensure successful improvement of quantitative traits. Certainly, the size of the
watermelon plant has discouraged commercial breeders from this approach, but public breeders should be
funded to pursue this objective. Populations improved for specific traits of interest and enriched of adapted
germplasm would then be readily useful to private breeders for inbred development and hybrid testing.
In order to maximize the usefulness of these populations, a precise estimation of the intercrossing
frequency in watermelon is needed. The design of proper field technique, including optimum plot size and field
layout, is needed to favor intercrossing and reduce self-mating in the populations.
Breeding for Production of Seedless Fruit
One of the greatest advances in watermelon breeding during the last century has been the development
of triploid seedless cultivars. This technique has provided a new product, highly appreciated by customers, and
highly emphasized by private breeders. However, the almost complete shift of the breeding industry towards
seedless types has greatly reduced breeding progress.
The development of triploid seed requires the separate and contemporary breeding of tetraploid and
diploid lines with similar characteristics that can be combined during hybrid production. The breeding of
tetraploid parents is greatly limited by the low fertility of the first generations after doubling of the chromosome
number. Thus, only few lines can be successfully advanced through a tetraploid breeding program, resulting in
higher emphasis in reselection within already available tetraploid germplasm, rather than breeding of new lines
and populations.
170