THE EFFECT OF LOW ROOT TEMPERATURE ON GROWTH AND LIPID-COMPOSITION OF LOW-TEMPERATURE TOLERANT ROOTSTOCK GENOTYPES FOR CUCUMBER

In the framework of research directed to diminish energy consumption of glasshouse cucumber production, three low temperature tolerant rootstock genotypes for cucumber were compared. Firstly, growth at low root temperature of one Cucurbita ficifolia and two Sicyos angulatus genotypes was studied to determine which was the one most suitable as a cucumber rootstock at suboptimal root temperatures. Secondly, differences in lipid composition were examined. Thirdly, lipid composition of these rootstock genotypes was compared with that of low temperature sensitive cucumbers (Cucumis sativus L.; cv. Farbio and CPO inbred lines 79345 and 81354) studied earlier, to determine whether observed differences in lipid composition were consistent with differences in growth at low temperature of related species. Plants were grown at an air temperature of 20-degrees-C d/12-degrees-C n and at constant root temperatures of 20-degrees-C, 16-degrees-C or 12-degrees-C. Although growth decreased at 12-degrees-C for all genotypes, both Sicyos angulatus genotypes were more tolerant to low root temperature than Cucurbita ficifolia. Low root temperature affected root lipid composition only. An increased phospholipid and a markedly lower sterol and sterol ester level resulted in a strongly decreased sterol/phospholipid ratio at 12-degrees-C. Growth at low root temperature was inversely related with the sterol/phospholipid ratio but no correlation between growth and sterol/phospholipid ratio of the rootstock genotypes within one temperature regime was observed. So, this ratio is not an appropriate selection criterion for growth capacity.