Cucurbit Genetics Cooperative Report 10:76-77 (article 39) 1987
Inheritance of Bitterness in Cucurbita pepo L.
Fenny Dane, A. G. Hunter, and O. L. Chambliss
Department of Horticulture and Alabama Agricultural Experiment Station,
Auburn University, AL 36849
Cucurbitacins are very bitter and toxic secondary plant substances which
can be found in roots, cotyledons and fruits of many cucurbit species. Synthesis
of the bitter principles is initiated with the onset of seed germination.
It increases rapidly in roots and cotyledons of up to 6 day old seedlings
after which it decreases (Rehm, 1960). Jaworski et al. (1985) found a decrease
in the cotyledons but not in the roots of Cucurbita pepo 'Blackjack'.
The inheritance of bitterness in C. pepo was ought to be controlled
by one major dominant gene (Grebenscikov 1954). Nonbitter (NB) fruits were
found on bitter (B) seedlings, however, which pointed to the action of a
suppressor gene (Rehm, 1960). In later studies Rehm (1968) found the gene
for fruit bitterness to be independent from the gene for seedling bitterness.
The occurrence of bitter fruit on 'Zucchini'-type summer squash in commercial
plantings prompted our genetic studies. Our aim was to determine the interrelationships
of genes controlling bitterness in roots, cotyledons and fruits and to develop
effective seedling screening techniques for the selection of NB genotypes.
Bitterness of the roots, cotyledons and fruits was evaluated organoleptically;
roots 4 days or more and cotyledons 6 days or more after germination. Thin
layer chromatography techniques (Gorski et al., 1968) could not be used
to distinguish B from NB roots and cotyledons on an individual plant basis.
Bitterness was detected in the seedlings of several C. pepo
cultivars. The following combinations of B and/or NB roots and cotyledons
With the exception of 'Cocozelle', a decline in root and cotyledon bitterness
could be detected in these cultivars and in bitter fruited 'Zucchini'-type
squash. Crosses between 'ESCN' and 'Black Zucchini' or 'Cocozelle' and backcrosses
to 'ESCN' showed the expected monogenic B:NB ratios in the roots and cotyledons
of 'ESCN' x 'Cocozelle', but not in 'ESCN' x 'Black Zucchini'. The lower
than expected degree of bitterness found in 'ESCN' x 'Black Zucchini' may
be attributed to the low quantity of cucurbitacins present in the B parent.
Crosses between 'Zucchini'-type squash and 'EPSN' differing in cotyledon
bitterness only showed the expected 3B:lNB ratio for cotyledon bitterness.
Our genetic studies with F4 and F5 selections of
bitter fruited 'Zucchini'-type squash were in general agreement with Rehm's
(1968) studies. Fruit bitterness was found to be controlled by one dominant
gene (Table 1). It segregated independently from genes controlling bitterness
in other plant parts. The low degree of bitterness found in the roots and
cotyledon points to a low concentration of cucurbitacins in these plant
The results indicate that bitterness in the root, cotyledons and fruit
of Cucurbita pepo appears to be controlled in each plant part
by a monofactorial dominant gene. Seedlings with nonbitter roots generally
had nonbitter cotyledons, while seedlings with bitter roots had non-bitter
or bitter cotyledons. The gene for cotyledon bitterness may be dependent
on the gene for root bitterness. Since fruit bitterness segregates independently
from seedling bitterness, selection against bitterness of the fruit can
not be done in the seedling stage.
- Grebenscikov, I. 1954. (2) Notulae cucurbitologicae. I. Zur Vererbung
der Bitterkeit und Kurztriebigkeit bei Cucurbita pepo L.
- Gorski, P.M., A. Jaworski, S. Shannon, and R. W. Robinson. 1986. Rapid
TLC and HPLC quantification of cucurbitacin C in cucumber cotyledons. HortScience 21:1034-1036.
- Jaworski, A., P.M. Gorski, S. Shannon, and R. W. Robinson. 1985. Cucurbitacin
concentrations in different plant parts of Cucurbita species as a
function of age. Cucurbit Genetics Coop. Rpt. 8:71-73.
- Rehm, S. 1960. Die Bitterstoffe der Cucurbitaceen. Ergebnisse der
- Rehm, S. 1968. Neuere Untersuchungen uber Cucurbitacine. Deutsche
Apotheker Zeitung 108:878.