Association of Seed Size and Dimensions with Fruit Shape in Cucurbita pepo
Harry S. Paris and Haim Nerson
Department of Vegetable Crops, Agricultural Research Organization, Newe Ya'ar Research Center, P.O. Box 1021, Ramat Yishay 30-095, Israel
Additional index words. pumpkin, squash, cultivar groups, fruit shape, seed dimensions
Abstract. The length, width, and thickness of seeds of 64 edible-fruited cultivars of Cucurbita pepo were measured. The seeds of the cultigens of C. pepo ssp. pepo were larger than those of C. pepo ssp. ovifera. In both subspecies, the cultivar groups having longer fruit had proportionally shorter seeds than those having round or flat fruit. Differences of considerably greater magnitude were observed in C. pepo ssp. pepo. Pumpkins had the longest, widest, and flattest seeds while zucchini cultivars had the shortest and plumpest seeds. Seeds of cocozelles and vegetable marrows were proportionally longer and flatter than those of zucchini seeds.
We thank H.D. Wilson (Department of Biology, Texas A&M University, College Station), Y. Asherov (Vegetable Cultigens and Seeds Organization, Samarkand, Uzbekistan), G.P. Silvestri (Centro Cooperativo di Sperimentazione Agraria, Fidenza, Italy), V. Hemleben (Biologisches Institut der Universität Tübingen, Tübingen, Germany), G. Nagy (Keszthely Agricultural University, Mosonmagyarovar, Hungary), F. Ignart (Tezier, Valence, France), and G. Santini (Società Agricola Italiana Sementi, Cesena) for supplying some of the seed samples used in this study and to Angelina Ginzburg of Newe Ya'ar, for measuring the seeds. Contribution No. 134/98 from the Agricultural Research Organization, Bet Dagan, Israel.
Cucurbita pepo L. is perhaps the most polymorphic species for fruit characteristics (Naudin, 1856), possessing great variation in fruit size, shape, and color (Duchesne, 1786). Mature fruit can range from several centimeters in diameter, as in wild and ornamental gourds, to well over 20 kg in weight, as in some pumpkins. They can be slim and long, exceeding 50 cm, as in many cocozelles, to nearly spherical, as in the pumpkins, to flat and scalloped, as in scallop squash. They can possess various intensities and shades of green, orange, or yellow and in patterns of striping and/or bicolor, with rinds that are smooth, with 20 longitudinal grooves, ten longitudinal furrows, ten longitudinal ribs, warted, netted, and/or wrinkled.
On the basis of fruit shape, the edible-fruited cultigens have been classified into eight groups: cocozelle, pumpkin, vegetable marrow, zucchini, acorn, crookneck, scallop, and straightneck (Paris, 1986). On the basis of variation in allozymes and seed morphology, C. pepo is considered to consist of two subspecies, C. p. ssp. pepo and C. p. ssp.
ovifera (Decker, 1988). Both subspecies consist of wild as well as cultivated forms. Of the cultivated forms, the cocozelle, pumpkin, vegetable marrow and zucchini groups belong to ssp. pepo while the other four groups belong to ssp. ovifera.
Decker and Wilson (1986) studied seed size and shape in 36 genotypes of C. pepo, most of them gourd forms but also 14 edible-fruited cultigens. They observed that the culinary forms possess larger seeds than the gourds, with pumpkins possessing the largest of all. Furthermore, the edible-fruited cultigens of C. p. ssp. pepo had larger seeds than their counterparts of C. p. ssp. ovifera.
From our familiarity with the seeds of cultivated, edible-fruited C. pepo it seemed to us that differences in size and shape occurred among individual seeds, among different seed lots, among cultivars, and especially among cultivar groups. We observed (unpublished) in zucchini squash differences in seed size among fruit of the same cultivar. These differences were associated with seed count, the size of the seeds being inversely associated with their number in the fruit.
Our objective was to study more comprehensively seed size and shape among edible-fruited C. pepo. For this purpose, we measured length, width, and thickness, as well as relative proportions of these dimensions, expressed as ratio of length to width, length to thickness, and width to thickness, of the seeds of 64 edible-fruited cultivars, eight from each of
Table 1. Seed source, group, and name of the 64 accessions of Cucurbita pepo sampled.
Country Source Group Name Supplier
U.S.A. Commercial Pumpkin Connecticut Field Ledden, Sewell, N.J.
U.S.A. Commercial Pumpkin Small Sugar Ledden, Sewell, N.J.
U.S.A Commercial Pumpkin Howden Harris, Rochester, N.Y.
U.S.A Commercial Pumpkin Jack O'Lantern Ledden, Sewell, N.J.
Portugal Commercial Pumpkin Porqueira Sampaio, Paços de Ferreira
Mexico Research Inst. Pumpkin Mexico Chiapas H.D. Wilson, Texas A&M
Uzbekistan Research Inst. Pumpkin Non-Kadi O.V.C.S., Samarkand
Yugolslavia Traveller Pumpkin Yugoslavia 7 ?
U.S.A. Commercial Vegetable marrow Clarita Petoseed, Saticoy, Calif..
Italy Commercial Vegetable marrow Faentina Ingegnoli, Milan
France Commercial Vegetable marrow Verte Petite d'Alger Abondance, La Verpillière
Japan Commercial Vegetable marrow Vegetable Spaghetti Sakata, Yokohama
Israel Commercial Vegetable marrow Beirut Aratan, Haifa
U.K. Commercial Vegetable marrow All Green Bush Asmer, Leicester, England
Italy Commercial Vegetable marrow Bianco S.A.I.S., Cesena
Uzbekistan Research Inst. Vegetable marrow Yantar O.V.C.S., Samarkand
U.S.A. Commercial Cocozelle Long Cocozelle Ledden, Sewell, N.J.
Italy Commercial Cocozelle Alberello di Sarzane S.A.I.S., Cesena
Italy Commercial Cocozelle Ortolano di Faenza C.C.S.A., Fidenza
GermaN.Y. Commercial Cocozelle Cocozelle Tripolis Samenzuchter, Marbach
Italy Commercial Cocozelle Striato Pugliese Ingegnoli, Milan
Italy Commercial Cocozelle Albatros S.A.I.S., Cesena
Italy Commercial Cocozelle Striato d'Italia S.A.I.S., Cesena
France Commercial Cocozelle Verte Non-Coureuse d'Italie Abondance, LaVerpillière
U.S.A. Commercial Zucchini Black Beauty Northrup King, Minneapolis, Minn.
U.S.A. Commercial Zucchini Black Zucchini Gurney, Yankton, S.D.
U.S.A. Commercial Zucchini Fordhook Zucchini Burpee, Doylestown, Pa.
U.S.A. Commercial Zucchini Green Magic Musser, Twin Falls, Id.
U.K. Commercial Zucchini True French Thompson & Morgan, Ipswich, England
Italy Commercial Zucchini Nero di Milano Horticola, Cesena
Italy Commercial Zucchini Verde di Milano Ingegnoli, Milan
Italy Commercial Zucchini Verde Lungo di Milano Semitalia, Umbria
U.S.A. Commercial Scallop Golden Bush Scallop Dessert, El Centro, Calif.
U.S.A. Commercial Scallop White Patty Pan Field, Shenandoah, Iowa
U.S.A. Commercial Scallop Benning's Green Tint Northrup King, Minneapolis, Minn.
U.S.A. Commercial Scallop Yellow Bush Scallop Gurney, Yankton, S.D.
Hungary Research Inst. Scallop Ovari Feher G. Nagy, Keszthely, Univ.
Czechoslovakia Traveller Scallop Czechoslovakia 1 ?
U.S.A. Commercial Scallop Sunburst Abbott & Cobb, Feasterville, Pa.
Russia Traveller Scallop Russia 1 ?
U.S.A. Commercial Acorn Bush Ebony Agway, Syracuse, N.Y.
U.S.A. Commercial Acorn Ebony Northrup King, Minneapolis., Minn.
Austria Commercial Acorn Toptable Planta Flor, Vienna
U.S.A. Commercial Acorn Mammoth Table Queen Northrup King, Minneapolis, Minn.
U.S.A. Commercial Acorn Royal Acorn Loft's, Bound Brook, N.J.
U.S.A. Commercial Acorn Table King Harris, Rochester, N.Y.
U.S.A. Commercial Acorn Table Queen Harris, Rochester, N.Y.
U.S.A. Commercial Acorn Tay-Belle Asgrow, Kalamazoo, Mich.
U.S.A. Commercial Straightneck Golden Girl Harris, Rochester, N.Y.
U.S.A. Commercial Straightneck Multipik Harris, Rochester, N.Y.
New Zealand Commercial Straightneck Goldzini Yates, Te Papapa, Auckland
U.S.A. Commercial Straightneck Early Prolific Straightneck Ledden, Sewell, N.J.
U.S.A. Commercial Straightneck Seneca Butterbar Gurney, Yankton, S.D.
U.S.A. Commercial Straightneck Lemondrop Asgrow, Kalamazoo, Mich.
U.S.A. Commercial Straightneck Castlegold Castle, Morgan Hill, Calif..
U.S.A. Commercial Straightneck Creamy Park, Greenwood, S.C.
U.S.A. Commercial Crookneck Pic-N-Pic Pan American
U.S.A. Commercial Crookneck Early Yellow Crookneck Twilley, Trevose, Pa.
U.S.A. Commercial Crookneck Dixie Park, Greenwood, S.C.
U.S.A. Commercial Crookneck Yellow Summer Crookneck Ferry Morse, Fulton, Ken.
U.S.A. Commercial Crookneck Supersett Harris, Rochester, N.Y.
U.S.A. Commercial Crookneck Early Golden Crookneck Field, Shenandoah, Iowa
U.S.A. Commercial Crookneck Early Summer Crookneck Loft's, Bound Brook, N.J.
U.S.A. Commercial Crookneck Ranger Dessert, El Centro, Calif..
Table 2. Group, cultivar, and sources of seeds of Cucurbita pepo accessions for which more than one seed stock was obtained.
Group Cultivar Seed sources
Cocozelle Striato d'Italia S.A.I.S., C.C. S.A., Horticola, Ingegnoli.
Cocozelle Alberello di Sarzane S.A.I.S. (2 samples), C.C.S.A., Horticola
Cocozelle Verte Non-Coureuse d'Italie Tezier (Valence, France), Clause, Abondance
Vegetable marrow Beirut Aratan, Hazera' (Haifa, Israel)
Vegetable marrow Verte Petite d'Alger (syn. Grey Zucchini) Northrup King, Ingegnoli, Gondian (Crest, France), Abondance
Acorn Royal Acorn Loft's, Twilley (two samples from Twilley)
Crookneck Early Summer Crookneck Loft's, Fredonia (Fredonia, N.Y., U.S.A.), Ledden
Straightneck Early Prolific Straightneck Ferry Morse, Twilley
the eight groups. For a few cultivars, seeds had been obtained from two or more sources. These different seed lots were also compared.
Materials and methods
Samples of 12 seeds each from 64 accessions of C. pepo, eight accessions from each of the eight cultivar groups, were measured with calipers. The 64 accessions sampled are listed in Table 1. Of those cultivars from which seeds had been obtained from more than one source, the seed stock selected was the first one that had been collected (of two sources) or one which had median and not extreme measurements (of three or more sources).
The cultivars for which more than one seed sample had been obtained are listed in Table 2, along with the sources of their seeds. The length, width, and thickness of each of twelve seeds of each cultivar from each of the seed sources were measured with a Somet, Inox (Czechoslovakia) calipers to the nearest tenth of a millimeter.
Results and discussion
The results for different stocks of the same cultivar are summarized in Table 3. Significant
differences in seed dimensions occurred among stocks of most of the cultivars tested. Differences had the greatest statistical significance and were most common in seed length but also occurred for seed width in half of the cultivars, and were detected for seed thickness in three of the eight cultivars. Significant differences were less common for relationships among these dimensions, for example, differences in length-to-width ratio were nonsignificant in all of the cultivars. Clearly, seeds among different stocks can differ in size, but are much less prone to differ in shape, as expressed by one dimension in proportion to another. Upon examination of the data (not presented) taken from each of the four stocks of 'Alberello di Sarzane,' it was observed that the significant differences in length-to-thickness and width-to-thickness ratios observed in this cocozelle cultivar were based on one of the four stocks being very different from the others. This had been one of the two stocks obtained from S.A.I.S. (Cesena, Italy). The company had stipulated on the seed packet that this stock was of a special strain of this cultivar.
The results for seed samples of 64 cultivars are presented in Table 4. The seeds of edible-fruited
Table 3. Value and significance of F tests for differences in seed dimensions among seed stocks of the same cultivar.
No. of Length Width Thickness
Subspecies Group Cultivar stocks (L) (W) (T) L:W L:T W:T
pepo Cocozelle Striato d'Italia 4 6.65** 2.64ns 1.23ns 2.13ns 1.43ns 2.44ns
pepo Cocozelle Alberello di Sarzane 4 6.29** 4.67** 5.91** 0.42ns 4.75** 4.94**
pepo Cocozelle Verte Non-Coureuse d'Italie 3 41.26** 19.15** 6.96** 2.52ns 1.20ns 1.30ns
pepo Vegetable marrow Beirut 2 1.51ns 0.85ns 1.07ns 0.23ns 0.12ns 0.33ns
pepo Vegetable marrow Verte Petite d'Alger 4 3.92* 0.42ns 1.07ns 2.56ns 1.06ns 0.69ns
ovifera Acorn Royal Acorn 3 5.72** 0.29ns 0.14ns 2.52ns 1.20ns 1.30ns
ovifera Crookneck Early Summer Crookneck 3 7.82** 5.70** 2.03ns 0.05ns 0.58ns 0.49ns
ovifera Straightneck Early Prolific Straightneck 2
ns,*,**Nonsignificant or significant at P = 0.05 or 0.01 using Duncan's multiple range test.
Table 4. Seed dimensions (mm) in eight groups of two subspecies of Cucurbita pepo, eight cultivars per group.
ssp. C. pepo
Vegetable ssp. C. ovifera
Group Pumpkin marrow Cocozelle Zucchini Acorn Scallop Straightneck Crookneck
Length 18.6 az 14.5 b 14.4 b 13.7 c 12.9 d 12.8 d 12.0 e 11.9 e
Width 10.2 a 8.3 b 7.9 c 8.4 b 7.8 c 7.7 cd 7.6 cd 7.4 d
Thickness 2.5 c 2.7 b 2.8 b 3.0 a 2.3 cd 2.2 d 2.3 d 2.3 d
Length:width 1.85 a 1.75 b 1.82 a 1.63 c 1.66 c 1.66 c 1.60 c 1.62 c
Length:thickness 7.65 a 5.53 bc 5.28 c 4.64 d 5.58 bc 5.77 b 5.46 bc 5.21 c
Width:thickness 4.17 a 3.18 d 2.91 e 2.84 e 3.37 bcd 3.48 b 3.43 bc 3.22 cd
zMean separations within rows by Tukey-Kramer honestly significant difference, 5% level of significance. Classification into subspecies and groups is from Decker (1988) and Paris (1986), respectively.
cultigens of C. pepo ssp. pepo were observed to be larger than those of C. p. ssp. ovifera (Table 3), in accordance with the report of Decker and Wilson (1986). Seeds of the pumpkin cultivars were the longest and widest of all.
Differences of greater magnitude were observed among the cultivar groups of ssp. pepo than among the cultivar groups of ssp. ovifera. For example, in ssp. pepo, pumpkin seeds averaged nearly 5 mm longer than zucchini seeds, but in ssp. ovifera, acorn squash seeds were only 1 mm longer than those of crookneck squash. Nonetheless, in both subspecies, the cultivar groups having long fruit had shorter seeds than those having round or depressed fruit.
Of the cultivar groups of ssp. pepo, the pumpkins were the most clearly differentiated from the others, their seeds being distinctly longer, wider, and flatter (Table 4). The zucchini cultivars were the next easily distinguished, being shorter and thicker than the others. Cocozelle seeds were proportionally long and narrow, similar to pumpkin seeds but plumper, and were narrower, longer, and thinner than those of zucchini seeds and narrower than vegetable marrow seeds. Overall, with regard to seed proportions, each of these four groups was well-defined (Table 4; Figure 1). The pumpkins clustered together clearly distinguished
Figure 1. Dendogram based on seed proportions (length-to-width ratio; length-to-thickness ratio; width-to-thickness ratio) for 32 cultivars of Cucurbita pepo ssp. pepo, eight per cultivar group, by Ward's method of hierarchical clustering using a SAS-JMP program: CO = cocozelle, VM = vegetable marrow, ZU = zucchini, PU = pumpkin. From top to bottom, the cultivars are for CO, 'Alberello di Sarzane', 'Ortolano di Faenza', 'Striato d'Italia', 'Long Cocozelle', 'Striato Pugliese', 'Verte Non-Coureuse d'Italie', 'Albatros', and 'Cocozelle Tripolis'; for VM, 'Beirut', 'All Green Bush', 'Bianco', 'Yantar', 'Clarita', 'Verte Petite d'Alger', 'Faentina', and 'Vegetable Spaghetti'; for ZU, 'Verde Lungo di Milano', 'Black Beauty', 'Nero di Milano', 'True French', 'Verde di Milano', 'Black Zucchini', 'Green Magic', and 'Fordhook Zucchini'; and for PU, 'Connecticut Field', 'Small Sugar', 'Jack O'Lantern', 'Howden', 'Nonkadi', 'Porqueira', 'Yugoslavia 7', and 'Mexico Chiapas'.
from the others (Figure 1). Seven of the eight zucchini cultivars clustered together. Half of the vegetable marrows clustered with the seven zucchini cultivars whereas the other half of the vegetable marrows clustered with the cocozelles and the remaining zucchini cultivar.
The results show a clear trend from proportionally flatter seeds in the pumpkins to less so in the vegetable marrows, to plumper seeds in cocozelles and plumpest in zucchinis. This trend corresponds with the appearance of each of these groups in historical records (Paris, 1989). Over centuries of squash breeding in C. pepo ssp. pepo, there has been a trend toward shorter, plumper seeds.
In proportions of length, width, and thickness, little differentiation to cultivar groups was observed with C. pepo ssp. ovifera (Table 4). This is in spite of the differences in fruit shape observed between the cultivar groups, differences which perhaps are more striking than in C. p. ssp. pepo.
Apparently, there is a relationship between proportions of fruit dimensions and proportions of seed dimensions. Longer, narrower fruit have shorter, plumper seeds. It is therefore tempting to suggest that fruit width, or more precisely seed-
cavity width, plays a restrictive role on seed length. In longer fruit, there is less room for the seeds to lengthen but more room for them to become plump than in round or depressed fruit. Nonetheless, other data (not presented) suggest that factors other than the size and shape of the seed cavity are also involved in determining the proportional dimensions of the seeds.
Decker, D.S. 1988. Origin(s), evolution, and systematics of Cucurbita pepo (Cucurbitaceae). Econ. Bot. 42:415.
Decker, D.S. and H.D. Wilson. 1986. Numerical analysis of seed morphology in Cucurbita pepo. System. Bot. 11:595607.
Duchesne, A.N. 1786. Courge, Cucurbita, p. 148159. In: J.B.P.A. de M. de Lamarck, Encyclopédie Méthodique, Panckoucke, Paris. Botanique vol. 2.
Naudin, C. 1856. Nouvelles recherches sur les caractères spécifiques et les variétés des plantes du genre Cucurbita. Ann. Sci. Nat. Bot. IV 6:573.
Paris, H.S. 1986. A proposed subspecific classification for Cucurbita pepo. Phytologia 61:133138.
Paris, H.S. 1989. Historical records, origins, and development of the edible cultivar groups of Cucurbita pepo (Cucurbitaceae). Econ. Bot. 43:423443.