Adaptation of the glasshouse cucumber to lower temperature in winter by breeding

The Institute for Horticultural Plant Breeding (IVT) has in 1974 initiated a program to select slicing cucumbers that grow and produce well at lower temperatures in winter. The goal was set at 20°C day, and 15°C night from the time of planting, while soil heating kept the root temperature around 20°C. The resulting saving of fuel costs amounts to 30–40°with cropping beginning at the usual time. Few out of hundreds of varieties from all over the world exhibited good growth in the selection environment. After four cycles of breeding and incorporation of Dutch slicer germplasm over 30 were developed with superior growth and fruit production, which were made available to the interested private breeding firms in The Netherlands in 1978. Early harvest of the best breeding lines at the low temperature equalled that of the control varieties at normal temperature. Most lines also gave promising yields in a 1979 trial with 12°C night temperature. Measurements of early growth at controlled fixed and alternating temperatures confirmed that outstanding lines grew faster than the control variety Farbiola. Changes in plant type may partly be responsible for the observed differences. Leaf area ratios (LAR) of the breeding lines were generally higher than those of the control variety at 20°C D/12°C N. Selection of fast growing plants at an early growth stage appeared to be possible.