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Cucurbit Genetics Cooperative Report 21:59-61 (article 21) 1998

Seed Development and Seed Fill in Hull-less Seeded Cultigens of Cucurbita pepo L.

Kelly Vining and Brent Loy

Department of Plant Biology, University of New Hampshire, Durham, NH 03824

Introduction. A breeding program to develop hull-less seeded cultivars of pumpkin has been ongoing at the University of New Hampshire since the early 1980s (3). The initial goal of the program was to develop high seed yielding cultivars for use in the snackseed industry. More recently (1,2), we have focused on increasing seed size, and have evaluated some promising hybrids that combine high yields with large seed size. A limitation of our breeding program has been an absence of basic information on seed development and seed fill, and on the relationship of seed maturity to perceived fruit maturity. In the present study we obtained information on bio,mass accumulation among seed organs (seed coat, embryo and endosperm) over the course of seed development.

Materials and Methods. Three cultigens were used: PI285611 (S3 ) which has large fruit (3 to 5 kg) and seed (210 to 250 mg/seed), NH29-13 (F9) which has small fruit (0.5 to 1.0 kg) and medium seed (140 to 170 mg); and NJ 1003, the F1 hybrid from the above lines, which has relatively large fruit (2 to 4 kg) and seed (180 to 220 mg). The field study was conducted in 1997 at the Woodman Horticultural Farm, Durham, NH, using a randomized complete block design with 6 blocks. Hand pollinations were made between 22 July and 7 August, and the resulting fruit were harvested on 13 sampling dates between 10 and 60 days post-anthesis (PA). Thirty-seed samples were removed from fruits collected 10 to 35 days PA, and 20 seeds per fruit were sampled thereafter. Seed coats, embryos and endosperm were separated under a dissecting scope, and data were collected on fresh and dry biomass of seed organs. These data were used to calculate percent dry matter (%DM) of seed organs and partitioning of dry matter within the whole seed.

Results and Discussion. Endosperm was detectable in all seeds between 10 and 35 days PA (Table 1); however, embryos were not large enough to efficiently dissect until 20 days PA. There was considerable variation in embryo size between 20 and 31 days PA, both among and within fruit. The bulk of the seed biomass (86 to 99.7%) was comprised of seed coat tissues between 10 (99.7%) and 25 (86%) days PA. Seed coat dry mater peaked at 20 to 25 days PA and then progressively declined until 45 to 50 days PA, agreeing with an earlier study (4). Embryo biomass increased rapidly from between 1 and 8% of total seed dry weight at 25 days PA to between 51 and 71% total seed dry weight at 35 days PA. Embryo weight as function of total dry weight at 35 days PA was greatest in the F1 hybrid, and lowest in the bush strain NJ29-13. This was surprising in view of the fact that NJ29-13 exhibited some orange color in fruit by 25 days PA, and apparent fruit maturity (skin totally orange) by 35 days PA. In contrast, F1 hybrid fruits did not begin to change color until 40 days PA and were not totally orange/yellow until 55 days PA.

Total dry seed biomass continued to accumulate in all genotypes until 55 to 60 days post-anthesis. Although there was considerable sampling variation, a substantial proportion (11 to 30%) of seed fill (increases in embryo weight, primarily cotyledonary tissues) occurred during the later stages of seed maturation (50 to 55 days PA in NJ 1003, 55 to 60 days in NH29-13 and PI285611) among all three genotypes. Again, in the case of NJ29-13, this seed fill occurred much later than perceived fruit ripeness as evaluated but changes in skin color. There were minor differences in the duration of seed fill among genotypes, but there were large differences in seed size and therefore in rates of seed fill. In PI285611, the mean embryo dry weight was 204 mg/seed at 60 days PA, and embryo biomass accumulated at a rte of 5.72 mg per day between 25 and 60 days PA. The corresponding values for NJ29-13 wee 136 mg/seed at 60 days PA and mean increases in biomass of 3.14 mg/seed/day between 28 and 60 days PA. For NH1003, embryo weight was 182 mg/seed at 55 days, and rate of seed fill was 5.07 mg/seed/day between 25 to 60 days PA. Because seed fill in NH1003 was largely complete by 55 days PA,its rate of seed fill was actually comparable to that of PI285611.

The results of this study show that embryo enlargement and seed fill occur at relatively late stages in seed development, and that substantial changes in seed fill can continue over a prolonged period of about 35 days. In some genotypes the period of seed fill extends well beyond the period of perceived fruit maturation as judged by changes in skin color from green to orange or yellow/orange.

Table 1. Dry matter accumulation in seed organs between 10 days post-anthesis until seed maturity.

Genotypes
Days post-anthesis
Seed coat dry biomass (mg/seed)
Endosperm dry biomass (mg/seed)
Embryo dry biomass (mg/seed)
Total dry biomass (mg/seed)
% Dry biomass of embryos
NH29-13
 
10
20.47
0.03
0.00
20.50
0.00
 
15
38.03
0.37
0.00
38.40
0.00
 
20
51.17
1.93
0.07
53.17
0.13
 
25
50.40
2.30
0.60
53.30
1.13
 
28
47.97
2.13
5.33
55.43
9.62
 
31
36.97
0.73
15.50
53.20
29.14
 
35
31.77
0.17
33.87
65.80
51.47
 
40
33.15
0.00
52.60
85.75
61.34
 
45
23.00
0.00
77.95
100.95
77.22
 
50
20.30
0.00
94.50
114.80
82.32
 
55
17.65
0.00
74.90
92.55
80.93
 
60
18.75
0.00
136.00
154.75
87.88
NH1003
 
10
23.10
0.07
0.00
23.17
0.00
 
15
34.73
0.57
0.00
35.30
0.00
 
20
50.67
2.57
0.13
53.37
0.25
 
25
44.30
2.37
4.27
50.93
8.38
 
28
42.50
1.53
18.67
62.70
29.77
 
31
33.33
1.03
27.27
61.63
44.24
 
35
23.50
0.03
59.87
83.40
71.78
 
40
22.15
0.00
82.55
104.70
78.84
 
45
24.45
0.00
131.40
155.85
841.31
 
50
18.35
0.00
123.35
141.70
87.05
 
55
17.50
0.00
176.00
193.50
90.96
 
60
14.75
0.00
181.85
196.60
92.50
PI85611
 
10
20.33
0.07
0.00
20.40
0.00
 
15
44.87
0.63
0.00
45.50
0.00
 
20
67.83
3.60
0.20
71.63
0.28
 
25
62.57
.013
3.77
69.47
5.42
 
28
57.23
2.50
17.00
76.73
22.15
 
31
45.90
1.43
31.07
78.40
39.63
 
35
37.20
0.57
52.17
89.93
58.01
 
40
28.35
0.05
98.10
126.50
77.55
 
45
31.50
0.00
154.30
185.80
83.05
 
50
21.70
0.00
151.35
173.05
87.46
 
55
21.65
0.00
171.65
193.30
88.80
 
60
20.20
0.00
204.15
224.25
91.00

Literature Cited

  1. Carle, R.B. and J.B. Loy. 1994. Heritability of seed size in hull-less seeded strains of Cucurbita pepo L. Cucurbit Genetics Coop Rept. 17:125-127.
  2. Carle, R.B. and J.B. Loy. 1995. Heritability of seed size and its association with fruit size in a hull-less seeded F2 population of Cucurbita pepo L. In: G. Lester and J. Dunlap (eds.), Proc. Cucurbitaceae 94: Evaluation nd Enhancement of cucurbit Germplasm, pp. 221-223. Gateway Publishers, Edinburg, TX.
  3. Loy, J.B. 1990. Hull-less seeded pumpkins: A new edible crop. In: J. Janik and J. Simon (eds.),Advances in New Crops, pp. 403-408. Timber Press, Salem. OR.
  4. Stuart, S.G. and J.B. Loy. 1988. Changes in testa composition during seed development in Cucurbita pepo L. Plant Physiol (Life Sci. Adv.) 7:191-195.
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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
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send questions to T.C. Wehner; last revised on 15 December, 2009