Regeneration of cucumber
Seed dormancy
Some cucumber accessions germinate irregularly. It is unknown whether this is caused by seed dormancy. Germination can sometimes be improved by cutting off the top of the seed.
Vernalization
No vernalization takes place during the regeneration of cucumber.
Sowing
Before sowing, seeds are given a heat treatment to avoid infection with seed-transmittable viruses like CGMMV.
Seeds are sown in seed trays with a soil mixture at 25°C, generally in February, but it is possible to sow between January and July. After 7 to 30 days, the seedlings are transplanted to Rockwool blocks and placed in a glasshouse nursery on tablets with a temperature of 23/20°C day/night and additional light.
Planting
About six weeks after sowing, the plants in the Rockwool blocks are placed on Rockwool bags at a distance of 50 cm in the row and 100 cm between the rows. The distance between rows can differ due to the substrate system used. The temperature in the greenhouse is keptat 23/20°C day/night. The plants are grown along wires. Per plant two stems are maintained since most cucumbers are indeterminate. Plants are pruned weekly.
The plants are grown in glasshouses free of pollinating insects so it is not necessary to take precautions for uncontrolled pollination. In case that a plant gives predominantly male flowers, it is possible to obtain female flowers by pruning. If pruning does not help, the plant can be sprayed with ethylene. Plants with only female flowers can produce male flowers after a treatment of the sprouts with 250 ppm silver nitrate. For seed production, a so-called chain pollination is carried out by hand. Per accession, plant no. 1 is crossed with plant no. 2, plant no. 2 with plant no. 3, and so on.
Generally 10 plants are used per accession for regeneration. In case of heterogeneous accessions or accessions with low seed production, more plants are used. The number of plants per accession is limited due to the high input in labour and capital.
Harvesting
Fruits are harvested about four months after sowing at the physiological ripe fruit stage. This is much later than the marketing stage. Per plant the aim is to produce two to four ripe fruits which can be harvested. Fruits are harvested in several rounds when they are ripe and stored for at least a week before seed extraction.
Pest and Disease Control
Biological control:
- Spider mites with Phytoseiulus persimilis
- Thrips with Phytoseiulus persimilis andOrius laevigatus
- White fly withAphidius colemani
- Aphids withEncarcia formosa
Non-preventive pesticide treatments:
- Spider mites, in case biological control is not effective
- Grey mould (Botrytis spp.)
- Gummy stem blight (Didymella spp.)
- Powdery mildew (Sphaerotheca fuliginea)
During regeneration, the plants are checked visually for diseases by the Dutch Plant Health Service. In case of doubt the plants are tested to determine the disease. Infected plants are removed.