ENVIRONMENTAL-EFFECTS ON GENETIC-VARIATION OF CHILLING RESISTANCE IN CUCUMBER

Environmental effects on genetic variation for chilling resistance wer e studied in nine cultivars and breeding lines (referred to as cultige ns hereafter) of cucumber (Cucumis sativus L.). Five experiments were carried out in controlled-environment chambers to measure the effects of growth temperature, photoperiod, duration of chilling, light level during chilling, and watering frequency on chilling resistance of seed lings at the cotyledon and first true leaf growth stages. Significant interactions were found between cultigen and all environmental factors studied except for the photoperiod and watering frequency. Cultigen r ank was affected by growth temperature before chilling, chilling durat ion, and light level during chilling, but shifts in rank were not cons istent. Genetic variation was largest when the plants were grown at 22 /18 degrees C, most pronounced after a chilling duration of 5 to 9 hou rs and a light level during chilling of 270 mu mol.m(-2).s(-1). Variat ion was larger at the first true leaf stage than at the cotyledon stag e. Differences among cultigens in chilling damage were largest 5 days after chilling. Therefore, it seems that testing for genetic Variation in chilling damage can be restricted to one set of environmental cond itions. We recommend the following conditions for screening cucumber f or genetic variation in chilling resistance: grow the plants at 22/18 degrees C, under a 9-hour photoperiod with a 3-hour night interruption , water them once daily, subject them at the first true leaf stage to a chilling treatment of 7 hours at 4 degrees C at a light level of 270 mu mol.m(-2).s(-1) and evaluate damage 5 days after treatment.