Responses of young cucumber plants to root and shoot temperatures.

Young cucumber plants were grown at all combinations of three shoot and three root temperatures (12, 18 and 24 degrees C). Growth and development of vegetative parts and fruits were studied after a temperature treatment of 14 days or 28 days. Shoot temperature has a positive effect on the rate of leaf development, while the rate of leaf initiation is influenced to a minor degree. There is only a small effect of root temperature on the rate of leaf appearance. The number of fruits is increased with increasing shoot and root temperature, the shoot temperature being more important than the root temperature. The total fruit fresh weight also increases with increasing shoot temperature; at 24 degrees C shoot temperature, the fruit weight shows an optimum at 18 degrees C root temperature. Distribution of dry matter is also dependent on root temperature and to a greater extent on shoot temperature. A shoot temperature of 18 degrees C is optimal for root growth, while 24 degrees C shoot or root temperature is sub-optimal for shoot growth. Increase in shoot temperature has a stronger positive effect on stem growth than on leaf dry weight. The relative effect of root temperature on stem growth equals that on leaf growth. Growth analysis shows that increase in relative growth rate at higher shoot and root temperatures under low light conditions is achieved by increasing the specific leaf area. This adaptation to changes in shoot or root temperature occurs within 14 days. ADDITIONAL ABSTRACT: Cucumber plants (cvs Farbio and Sandra, both F1 hybrids) were grown at 12, 18 and 24 deg C shoot and root temperatures in all combinations. The number of fruits was increased with increasing shoot and root temperature, the shoot temperature being the more important. Total fruit fresh weight also increased with rising shoot temperature. At 24 deg shoot temperature, however, fruit weight was optimum with 18 deg root temperature. Also, at 24 deg shoot temperature, the lower the root temperature the more fruits were present at a given leaf number. A shoot temperature of 18 deg was optimal for root growth but 24 deg shoot or root temperature was still suboptimal for shoot growth. An increase in shoot temperature had a stronger positive effect on stem growth than on leaf dry weight. The relative effect of root temperature on stem growth was equal to that on leaf growth. Growth analysis showed that leaves became thinner at higher temperatures. This adaptation to changes in shoot or root temperature occurred within 14 days. Cvs showing the highest specific leaf area at the desired temperature seem to be the best qualified to give the optimal relative growth rate at the low light intensities prevailing in early spring. (Abstract retrieved from CAB Abstracts by CABI’s permission)