Effect of Pot Size on Growth and Flowering of Cucumbers in the Greenhouse

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Cucurbit Genetics Cooperative Report 9:47-50 (article 13) 1986

Todd C. Wehner and Rufus R. Horton, Jr.
Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609

Cucumbers grow rapidly compared to most crop species, so that it is possible to get 3 to 5 generations per year in a breeding program using greenhouse facilities. Four generations per year is possible if the plants flower within 6 weeks of planting so that pollinations can be made in time to allow up to 6 weeks for the seeds to mature and up to 1 week to harvest and replant the greenhouse. It is often difficult to stay on a 13-week generation time due to the extra labor requirements of planting, pollination and harvest times.

Researchers with other crops have been successful in getting more generations per year by crowding the plants. Goulden (2) proposed the idea of using growth chambers to speed the growth of small grains by crowding. Grafius (3) applied the method by planting barley and oats in greenhouses using sand culture. Water was applied as needed, but fertilizer was given only 2 to 3 times. The plants remained small and produced only 0 to 4 (rarely 0) seeds per inflorescence. Many plants could be advanced in a small space in less time under this system. The system was modified by Brim (1) for his single-seed descent breeding method. Robbins and Pharr (4) grew cucumber plants in pots ranging from 0.4 to 5.9 1 in volume to restrict root growth. Water and nutrients were provided to prevent stress, and shoots were given unlimited growth space in the greenhouse. However, the shoots were proportionally smaller on plants with restricted root size (root/shoot ratio remained constant).

Peterson (personal communication) found that seeds could be harvested 4 weeks after pollination, cleaned with high pressure water, dried for 1 day, soaked in acetone for 1 day, incubated at 32 ˚ C in petri plates containing moist vermiculite, and transplanted to pots 1 day later. That method saves 2 weeks on post-pollination seed development time, and 1 week on fermentation, drying and packeting time. Thus, with gynoecious plants, it is possible to go from seed to seed in 10 weeks for 5 generations per year.

In working with genotypes that grow fairly large, and are not as rapid to flower and set seed, it would be desirable to reduce further the generation time. It is possible that if cucumber plants were crowded into a small space they would grow smaller, flower faster, and set seeds sooner than normal. The objective of this study was to determine whether growing plants in small pots could reduce the generation time of cucumbers in the greenhouse.

Methods. The experiment was a randomized complete block with 2 cultivars, a gynoecious inbred pickle (Gy 14A) and a monoecious inbred sliver (Poinsett 76). Plants were grown in one of 4 pot sizes (10, 13, 15, 0or 20 cm diameter), and fruits were either held on the plants without watering 2, 4, or 6 weeks after pollination (summer, 1983), or harvested 2, 4, or 6 weeks after pollination (spring, 1984).Data were collected at fruit harvest time. The vine length, fruit weight, number of seeds per fruit, weight per seed, and percentage of germination at 22 ˚ C were measured. Also, the number of days from planting to first pistillate flower was recorded.

Results. Plants grown in large pots had longer vines and heavier fruits than those grown in small pots (Tables 1 and 2). The larger fruits had more seeds, but the weight per seed did not change. Days to flower and percentage of germination of the harvested seeds did not change with pot size, except that no seeds were produced from fruits harvested 2 weeks after pollination. Although ‘Poinsett 76’ flowered as soon as Gy 14A, the flowers were staminate for the first 5 to 10 days (data not shown). Thus, for monoecious lines, self-pollinations cannot be made until 41 to 49 days after planting (Tables 1 and 2). The extra 1 to 2 weeks time for pollination of monoecious lines would make it possible to get 4 generations a year, but not 5 (as is possible for gynoecious lines).

Thus, it is possible to change the size of the plant and the number of seeds per fruit by using larger pot sizes. However, plants grown in small pots do not flower or reach mature seed stage sooner than those grown in large pots. Although there were occasional problems of small seeds and poor germination of seeds from plants grown in 10 cm diameter pots, it was possible to get sufficient seed numbers from plants grown in 13 to 20 cm diameter pots. Two weeks after pollination, watering could be stopped and seeds would still develop properly (Table 1). However, fruits harvested 2 weeks after pollination did not have viable seeds (Table 2). It required 4 weeks for seeds to develop sufficiently for good germination.

Plants grown in 13 cm pots with fruits harvested 4 weeks after pollination provided 90 to 296 seeds per fruit that were plump and germinated well. That appeared to be the minimum satisfactory system of the treatment combinations tested.

Table 1. Effect of pot size nad weeks to end of irrigation on plant and fruit growth for summer, 1983 greenhouse cropz .

Cultivar

Weeks of watery

Pot dia., (cm)

Vine length (cm)

Fruit weight (g)

Seed no.

Weight per seed (mg)

% germination

Days to 1st flower
Gy 14 A 2 10 102 25 74 22 100 37
13 136 23 52 27 100 38
15 180 35 61 21 100 38
20 308 103 213 28 100 37
4 10 132 37 82 16 98 38
13 135 28 90 21 98 40
15 206 65 60 27 100 38
20 290 50 67 26 100 41
6 10 75 20 45 26 95 37
13 126 40 61 25 98 37
15 236 68 197 18 100 38
20 390 95 219 28 100 38
Poinsett 76 2 10 176 16 39 25 100 49
13 192 40 125 23 100 49
15 264 53 179 25 100 43
20 306 75 172 27 100 49
4 10 108 28 99 16 95 49
13 157 48 142 21 100 49
15 323 65 102 27 100 47
20 300 120 118 27 100 49
6 10 204 45 87 23 100 48
13 220 40 149 25 100 43
15 347 117 202 28 100 43
20 451 118 210 24 100 49
LSD (5%) 86 31 109 10 4 3
CV (%) 19 27 55 20 2 5

z  Data are means of 2 replications.
y Irrigation of pots stopped 2, 4, or 6 weeks after pollincation.

Table 2. Effect of pot size and weeks to harvest on plant and fruit growth for summer, 1984 greenhouse cropz.

Cultivar

Weeks to harvest

Pot dia. (cm)

Vine length (cm)

Fruit weight (g)

Seed no.

Weight per seed (mg)

% germination

Days to 1st flower
Gy 14 A 2 10 74 201 0 0 0 37
13 102 411 0 0 0 29
15 107 347 0 0 0 35
20 108 333 0 0 0 33
4 10 87 350 160 26 100 36
13 92 496 228 26 100 36
15 110 567 251 28 100 35
20 126 522 231 32 100 36
6 10 91 354 189 22 88 35
13 100 507 225 26 100 35
15 107 595 221 29 93 34
20 14 624 218 29 100 36
Poinsett 76 2 10 158 170 87 12 50 46
13 144 291 0 0 0 45
15 172 418 0 0 0 43
20 218 435 0 0 0 45
4 10 122 366 234 14 45 46
13 164 534 296 25 100 45
15 182 532 197 25 90 44
20 195 665 230 28 100 45
6 10 176 439 277 18 85 45
13 176 631 260 27 100 42
15 193 727 235 29 100 41
20 154 641 311 26 98 45
LSD (5%) 36 150 143 5 43 4
CV (5) 13 16 45 10 34 6

z  Data are means of 2 replications.

Literature Cited

  1. Brim, C.A. 1966. A modified pedigree method of selection in soybeans., Crop. Sci. 6: 220.
  2. Goulden, C.H. 1939. Problems in plant selection. p. 132-133. In R.C. Punnett (ed.), Proc. 7th Internat. Genet. Cong. Cambridge Univ. Press, London.
  3. Grafius, J.E. 1965. Short cuts in plant breeding. Crop Sci. 5: 377.
  4. Robbins, N.S. and D,M. Pharr. 1985. Effect of restricted roots on shoot growth and carbohydrate metabolism of Cucumis sativus L. leaves. HortScience 20(3) : 536 (abstr.).