Study On Tolerance Ability Of Cucumber Under Low Temperature And Poor Light Stress And The Seedling Stage Evaluation Method

Four ecotype cucumber cultivars including European greenhouse type, European cross Asian greenhouse type, Asian greenhouse type, Asian open-field type were employed in the study on the regulations of photosynthetic rate, efficiency of conversion of light energy of chloroplasts, chloroplyll content, chla/chlb, accumulation of leaf area, accumulation of dry weight, electrolyte leakage rate, cold injury index under low temperature and poor light condition. Based on the result, a practical and operational cucumber early stage evaluating method for the adaptability to low temperature and poor light stress has been developed. The results are as follows:1 Sub-optimal temperature (20C/12C) and critical low temperature (15C/7C) were two different stress for the growth and development of cucumber. It is observed that single sub-optimal temperature slowly decreased the photosynthetic metabolite of cucumber seedling and slightly affected the activity of PSII. Critical low temperature quickly decreased the photosynthetic metabolite and probably injured the PSII. Obvious cold injury symptom appeared after 5--10days treatment.2 At the beginning, single poor light treatment can induce the poor light adaptability of cucumber seedling, but as the treatment extending, the activity of photosynthesis was affected, poor light was a dominant factor and sub-optimal temperature strengthened the stress in the combination treatment of sub-optimal and poor light. For the combination of poor light and critical low temperature treatment, critical low temperature was a dominant factor, poor light slightly reduced the effect of critical low temperature on seedling.3 The cultivars of this experiment have different expression under sub-optimal, critical low temperature and poor light. European greenhouse cucumber was more tolerant to poor light but more sensitive to low temperature, especially critical low temperature than Asian greenhouse cucumber. European cross Asian ecotype cultivars was tolerant not only low temperature but also to poor light, which seems aggregated two ecotypes' virtues. The results also indicated that Asian open-field ecotype was not tolerant to the both stress above.4 The results above indicated that the tolerance to poor light and low temperature are two independent characters of cucumber. So they need be evaluated separately. During this study, we designed a multiple evaluating system. First step, using the accumulation of leaf area to evaluate the tolerance ability under poor light or the combination of poor light and sub-optimal temperature. Second step, after first step treatment, using the same seedlings , critical low temperature tolerance ability can be evaluated by investigating the cold injury index. Ideal result have gained by using this evaluating system on the selection of cucumber inbred lines and relative inheritance studies.