Table of Contents
Loy, J.B. 1990. Hull-less seeded pumpkins: a new edible snackseed crop. p.
403-407. In: J. Janick and J.E. Simon (eds.), Advances in new crops. Timber
Press, Portland, OR.
Hull-less Seeded Pumpkins: A New Edible Snackseed Crop
J. Brent Loy
- SELECTIVE BREEDING TRAITS
- Inheritance of Seedcoat Development and Color
- Plant Fruiting and Growth Habit
- PLANT DENSITY AND YIELD COMPONENTS
- PERFORMANCE OF ADVANCED SELECTIONS
- Table 1
- Table 2
- Fig. 1
- Fig. 2
- Fig. 3
Pumpkin seed (Cucurbita spp.) are consumed as a snack in many cultures
throughout the world, and the seed is especially popular in Central American
countries where strains have been selected primarily for edible seed use.
World production of Cucurbita seed for food use is meager, however,
because hand dehulling is necessary for obtaining marketable seed and there has
been little effort to improve seed yields.
Tschermak-Seysenegg (1934) reported a mutant trait in the seedcoat of C.
pepo L. in which the seedcoat was much reduced in thickness. The "naked
seed" trait permitted more efficient extraction of vegetable oil and seed could
be consumed directly without the necessity of dehulling. Genetically
"hull-less" seed produce all seedcoat tissue layers, but secondary wall
thickening is reduced in the outer tissues (epidermis, hypodermis, and
sclerenchyma). As mature hull-less seed dry, the outer tissues collapse,
producing a thin seedcoat (Stuart and Loy 1983).
Pumpkin seed are rich in both oil and protein; oil contents are generally in
the 40 to 50% range (Bemis et al. 1968, Jacks et al. 1972) and protein content
ranges from 30 to 40% (Jacks et al. 1972, J.B. Loy unpubl.). The amino acid
content of pumpkin seed protein is not as well utilized as soybean protein
(Zucker et al. 1958), being low in methionine, threonine, and tryptophan
(Bressani 1963, Robinson 1975). Limited studies indicate that pumpkin seed oil
is highly unsaturated and semi-drying (Lazos 1986). In the United States,
Curtis (1947) recognized the potential value of hull-less seeded pumpkins for
producing a high quality vegetable oil, for use as a snackseed, and for making
a sandwich spread. He initiated a breeding program at the University of
Connecticut to improve seed yields of pumpkin, but did not remain in
Connecticut long enough to carry the project to fruition.
As a result of sampling pumpkin seeds at various trade shows, I observed that
roasted seed have excellent consumer appeal. Moreover, in the U.S. alone, the
potential market for new and superior products in the confectionery trade
(snacks, trail mixes, granola cereals, salad bars, etc.) is huge. For example,
185,000 metric tons of sunflower were marketed in the U.S. for this purpose in
1981 (Lusus 1985). Also, use of pumpkin seed in developing countries could
provide a concentrated food source, high in protein and energy value.
In 1977, I began investigations on the genetics and breeding of hull-less
seeded pumpkins and soon thereafter attempts to develop high seed-yielding
strains suitable for supporting a snackseed industry
Several inheritance studies conducted in the early 1950s (Heinisch and
Ruthenberg 1950; Mudra and Neuman 1952; Schoeniger 1950, 1952, 1955; Weiling
and von Becherer 1950) produced conflicting interpretations as to the mode of
inheritance of the hull-less condition. More recent work by Stuart (1983)
showed convincingly that a single recessive gene conditions the existence of a
thin, parchment like seedcoat. At least two additional modifying genes, one of
which appears to be dominant (J.B. Loy unpubl.), further reduce the degree of
seedcoat development. In seed classified as completely hull-less, the outer
seedcoat layers are reduced to the extent that seed take on the appearance of
the inner seedcoat layer (chlorenchyma) which is normally dark green (Fig. 1, 2). I have found two color variants of chlorenchyma issue, light green,
recessive to dark green, and yellow, recessive to both dark green and light
green. When the outer seedcoat is partially developed (monorecessive
condition) seedcoats appear grey against a green chlorenchyma background and
tan against a yellow chlorenchyma background.
I am developing strains with the bush rather than vine habit of growth for
several reasons. Bush plants appear to be more productive than vine plants
because of a higher harvest index and adaptability to higher density plant
culture (Broderick 1982). Bush plants set fruit around the crown of the plant
resulting in more uniform ripening and easier harvesting.
Most hull-less seeded plant accessions currently available have moderate to
large fruit size, and some of the large-fruited strains have a high seed yield
per fruit. However, when seed yield is evaluated in terms of seed weight per
kg of fruit, I have obtained the highest yields in small-fruited (0.5 to 1.5
kg) selections. Moreover, small-fruited lines tend to set fruit better, set
fruit earlier, and set a larger number of crown fruit than lines bearing large
fruit. Although large seed size is often associated with large fruit, there
appears to be no genetic or physiological barriers to developing large-seeded
strains with small fruit.
To evaluate components of yield, a spacing trial was conducted in 1986 with two
F5 strains of pumpkin, NH14-40-6 and NH55-7-20. Plant density was varied by
using gradient density plots in which row width was kept constant at 0.9 m and
within row subplots were arranged in progressively decreasing within row
spacing from 1.5 to 0.3 m. This produced plant populations between 7,890 to
35,880 plants/ha. Subplots consisted of 5 data and 2 guard plants. Seed
yields were low in 1986, but the spacing results revealed important
relationships between plant density and components of yield among bush lines.
With both strains, per plant yields decreased significantly with increasing
plant density (Fig. 3). On the other hand, seed yield per unit area increased
with plant density (although due to extreme variability within a few plots,
linear regressions were not significant at P = 0.05).
Some important components of yield and their relationship to plant density are
given in Table 1. Fruit number, and to a lessor extent, mean fruit weight
decreased with increasing plant density in both strains. Seed yield per fruit
usually decreases with fruit size, but this relationship was not consistent in
1986. Plant spacing and fruit size had no effect upon seed size, although I
have observed that seed size decreases in extremely small fruit (<0.3 kg).
An important criterion for assessing the efficiency with which a plant
partitions photosynthates into seed is the Seed Index (SI) or ratio of seed dry
weight to total fruit dry weight. Within the strains used for the spacing
trial, SI's were low and variable, and showed no relationship to plant density.
A third cycle of snackseed selections has been derived from a cross of
NH14-40-6 to a seedy, partially hull-less strain, NH54-10-14. The major
selection criteria have been small fruit, thin pericarp, high seed weight per
kg fruit, high harvest index, vigorous growth at close spacing, good pollen
production, and crown fruit set. A summary of performance of individual
selections and selections within lines in F2 and F3 generations obtained in
1986 and 1987 is given in Table 2. The most noteworthy observation is that
seed yield (g/kg fruit wt) and seed index have been dramatically improved as
compared to the lines used in the spacing trial. Furthermore, these lines show
improved germination under field conditions, more vigorous growth, and several
are adaptable to high density culture. Seed yields were, in general much
higher in 1987 (F3) than in 1986 (F2). However, seed indices were not higher
because pericarp dry matter was also higher.
It was expected that potential seed yields of advanced lines could be evaluated
in 1988. Eighteen F4 and F5 snackseed lines were grown in rows 1.8 m apart and
20 m long with 0.3 to 0.6 m between plants. However, adverse weather
conditions for pollination and fruit set markedly decreased crown set and seed
yields, and few, plant selections were made. Nonetheless, seed were harvested
from fruit of 4 lines which looked most productive and had the least amount of
green fruit by mid-September. Factoring near-ripe, immature fruit (17 to 28%
of total harvest) into total yield estimates, seed yields of 1,100 to 1,500
kg/ha were obtained. Yields of this magnitude would be sufficient for
supporting commercialization of hull-less pumpkin seed for a confectionery
Pumpkin seed with reduced seedcoat tissues, termed hull-less, can be eaten
directly without dehulling, and make a delicious roasted seedsnack. Within
Cucurbita pepo there is enormous genetic variation in plant growth
habit, fruit type, and seed traits which can be utilized for improving both
seed yield and various culinary traits of seed such as taste, size, color, and
degree of fiber. Current snackseed pumpkin breeding lines developed at the New
Hampshire Agricultural Experiment Station during the past 10 years show
excellent potential for use in developing a snackseed industry
- Bemis, P.W., W.J. Berry, J.M. Kennedy, D. Wood, M. Moran, and J.A. Deutschman.
1968. Oil composition of Cucurbita. J. Amer. Oil Chem. Soc.
- Bressani R. 1963. Nutritive value of pumpkin seed. Essential amino acid content
and protein value of pumpkin seed (Cucurbita farinosa). J. Agric. Food
- Broderick, C.E. 1982. Morpho-physiological factors affecting plant productivity
in bush and vine forms of winter squash (Cucurbita maxima Duch.). Ph.D.
Thesis, Univ. New Hampshire, Durham.
- Curtis, L.C. 1948. The use of naked seed in Cucurbita pepo as a source
of high quality liquid vegetable fat, as a high analysis protein, as a new
confection, and as a sandwich spread. Proc. Amer. Soc. Hort. Sci. 52:403-406.
- Heinisch, O., and M. Ruthenberg. 1950. Die Bedeutung der Samenschale fur die
Zuchtung der Olkurbis. Z. Pflanzenzucht. 29:159-174.
- Jacks, T.J., T.P. Hensarling, and L.Y. Yatsu. 1972. Cucurbit seeds: I.
Characterizations and uses of oil and proteins. A review. Econ. Bot.
- Lazos, E.S. 1986. Nutritional, fatty acid and oil characteristics of pumpkin
and melon seeds. J, Food Sci. 51:1382-1383.
- Lusus, E.W. 1985. Sunflower seed protein, p. 393-433. In: A.M. Altschul and
H.C. Wilcke (eds.). New, protein foods. vol. 5. Academic Press, New York.
- Mudra, A., and D. Neumann. 1952. Probleme und ergebwisse der Muncheberger
Olkurbiszuchtung. Züchter 22:99-105.
- Robinson, R.G. 1975. Amino acid and elemental composition of sunflower and
pumpkin seeds. Agron. J. 67:541-544.
- Schöeniger, G. 1950. Genetische Untersuchungen an Cucurbita pepo.
- Schöeniger, G. 1952. Vorlaufige Metteilung uber das Verhalten der testa-
und farbgene bein verscheidenen Kreuzungeninnerhalb der Kurbisart, Cucurbita
pepo L. Züchter 22:316-337.
- Schöeniger, G. 1955. Beobachtungen zur vererbung gewisser testa
eigenschaften bei Cucurbita pepo L. Züchter 22:316-337.
- Stuart, S.G. 1983. Comparative biochemical antigenetic studies of testa
development in normal and hull-less phenotypes of pumpkin (Cucurbita
pepo L.). Ph.D. Thesis, Univ. New Hampshire, Durham.
- Stuart. S.G. and J.B. Loy. 1983. Comparison of testa development in normal and
hull-less seeded strains of Cucurbita pepo L. Bot. Gaz. 144:491-500.
- Tschermak-Seysenegg, E. 1934. Der kurbis mit schalenlosen samen eine
beachtenswerte olfrucht. Wiener Landwirts. Z. 84:7-15.
- Weiling, F. and E. Prym von Becherer. 1950. Zur factorenanalyse der
testaausbildung beim kurbis. Ber. Deut. Bot. Ges. 63:147-148.
- Zucker, H., V.W. Hays, V.C. Speer, and D.V. Catron. 1958. Evaluation of pumpkin
seed meal as a source of protein using a depletion-repletion technique. J.
Table 1. Yield components for two New Hampshire breeding lines at 5
plant densities in a gradient density spacing trial, 1986.z
zValues ±SD for 3 replications
| ||Plant density/m2|
|Yield component ||0.8 ||1.02 ||1.43 ||2.39 ||2.59|
|Fruit (no./plant) ||3.5±0.6 ||2.7±0.5 ||2.1±0.2 ||2.1±0.1 ||1.5±0.3|
|Mean fruit wt (kg) ||1.2±0.1 ||1.2±0.1 ||1.0±0.1 ||0.9±0.04 ||0.8±0.1|
|Seeds (g) /fruit ||17.1±1.7 ||18.0±2.2 ||21.0±4.5 ||14.4±0.3 ||14.6±1.4|
|Seed wt(g/100) ||9.8±1.2 ||9.7±1.3 ||11.2±1.2 ||10.0±0.2 ||10.8±0.6|
|Seed Index (SI)y ||24.7±2.3 ||22.7±1.4 ||28.2±3.9 ||27.1±1.9 ||29.4±7.1|
|Fruit (no./plant) ||3.6±0.6 ||4.2±0.4 ||3.2±0.6 ||1.5±0.4 ||1.7±0.3|
|Mean fruit wt. (kg) ||1.2±0.1 ||1.2±0.1 ||1.1±0.1 ||1.0±0.1 ||0.9±0.03|
|Seed (g) fruit ||20.4±6.3 ||19.4±5.7 ||15.5±5.3 ||22.9±9.1 ||15.8±4.4|
|Seed wt. (g/100) ||10.8±1.7 ||10.4±0.5 ||9.9±1.0 ||11.3±0.7 ||11.3±1.3|
|Seed index (SI) ||25.3±1.0 ||22.6±4.0 ||20.4±12.3 ||29.2±6.5 ||23.3±8.1|
ySeed index (SI) = seed dry wt/fruit dry wt x 100
Table 2. Yield components for advanced snackseed selections.
|Breeding line |
|Mean fruit weight (kg) ||% Dry matter pericarp ||g seed/kg fruit ||Seed index|
|614-6 ||0.91 ||5.8 ||56.7 ||51.7|
|614-100 ||1.15 ||6.2 ||41.0 ||42.0|
|614-213 ||1.12 ||7.0 ||46.4 ||42.0|
|614-226 ||0.95 ||8.1 ||72.7 ||48.0|
(Ave±SD, 5 selections)
|0.66±0.16 ||7.9±3.3 ||65.3±11.5 ||49.4±4.8|
(Ave±SD, 4 selections)
|0.87±0.23 ||8.9±4.5 ||63.1±20.9 ||44.6±13.8|
(Ave±SD, 2 selections)
|0.61±0.06 ||10.1±4.5 ||63.4±5.2 ||42.8±13.4|
(Ave±SD, 5 selections)
|0.67±0.13 ||7.4±1.9 ||64.4±23.9 ||49.8±11.9|
||Fig. 1. Seedcoat phenotypes of air dried seed of C. pepo. Upper
row = normal, hulled seed; second and third rows = partially hull-less seed;
bottom row = completely hull-less seed.|
Fig. 2. Seedcoat phenotypes in hull-less strains of C. pepo,
illustrating differences in seed size, shape, and degree of seedcoat
development in seed margins.
Fig. 3. Relationship of seed yield to plant density for two F5 breeding lines (1986). Open symbols = NH55-7-20; closed symbols = NH14-40-6. R2 for g seed yield per plant was 0.93 for NH14-40-6 and 0.89 for NH55-7-20. R2 for g
seed yield per m2 was 0.82 for NH14-40-6 and 0.87 for NH55-7-20.
Last update September 4, 1997