Watermelon
Crop Information
Heterosis and Combining Ability for Yield
- by Gabriele Gusmini and Todd C. Wehner
- Department of Horticultural Science
- North Carolina State University
- Raleigh, NC 27695-7609
Today, watermelon breeders are less interested in studying
heterosis and/or general (GCA) and specific (SCA) combining
ability, because hybrids have proven their advantage for
protection of the parents. Furthernore, seedless cultivars
are in high demand and can be produced only as triploid
hybrids. However, in the future it might be possible to
develop transgenic diploid seedless watermelons. In that
case, the question of the advantage in using heterotic hybrids
vs. inbred cultivars will still be pertinent and important.
Many Indian scientists in the 1950s and 1960s showed heterosis
in watermelon, making hybrid seeds the predominant products
in the watermelon seed industry. These studies measured
heterosis as well as GCA and SCA in watermelon, but they
were based on diallel or top crosses of elite inbreds, not
a random set of lines from a population. More recent studies
often included only a small number (Nmax=10) of non-randomly
chosen elite cultivars as parents, so the results are valid
only for those specific crosses and are not generally applicable.
Nevertheless, taken as a group, these studies indicate the
presence of heterosis in watermelon and the importance of
GCA in the choice of parents for hybrid production.
In a more recent study in Brazil, Dr. F.F. de Souza and
his group tested seven intercrossing populations with evaluation
of reciprocal crosses. They observed significant GCA, SCA,
and reciprocal combination effects, along with additive
effects. In a further effort, they evaluated GCA and SCA
for tetraploid females crossed with diploid males for the
production of triploid seeds. They recorded a higher magnitude
of GCA effects than SCA effects and strong additive effects
for yield components.
Environmental factors such as irrigation or general water
availability on yield also seem to be important in contrasting
inbred cultivars vs. hybrids. I.e., in Florida in 1985 Dr.
B.B. Rhodes observed that watermelon hybrids outyielded
inbred cultivars only in irrigated fields, but quality was
higher among the inbred cultivars in dry conditions.
