Study On Identification Index System Of Low Temperature And Poor Light Adaptability Of Cucumber And Mapping QTL Controlling Poor Light Adaptability

Sixteen cucumber cultivars with different adaptability to lower temperature and poor light were employed in this paper, including European greenhouse type, European cross Asian greenhouse type, North China greenhouse type, North China open-field type. Indexes on photosynthetic metabolite, physiological and biochemical, morphological under low temperature and poor light were measured. An efficient early stage identification method and evaluation system for low temperature and poor light adaptability have been developed and used in the germplasm selection and QTL mapping. The results are as follows.1. The reaction of cucumber seedling to sub-optimal temperature (lower temperature) and critical low temperature indicated that the influence of both stress to cucumber were obvious different. The variation of Fv/Fm and M peak under lower temperature or accompanied with poor light showed that the PS II system didn't be harmed under the stress.The variance of accumulation of leaf area among various cultivars under the stress of low temperature or poor light could be served as the indicator to represent reliably the adaptability of the cultivars to the stress above. While the critical low temperature may lead to the decrease of Fv/Fm and the disappear of M peak, and also provide a much stronger stress force to the cucumber seedlings. It resulted in an array of chilling injury symptom ranged from the lesion on leaves to death of seedlings, by which the chilling injury index can be calculated. The chilling injure index can serve as indicator of adaptability under critical low temperature in cucumber. It was obvious that the adaptability to lower temperature and critical low temperature are two relative independent character. The variation of proline content, root activity and electrolyte leakage rate under critical low temperature and the variation of chlorophyll content and Fv/Fm under low temperature and poor light are very important for study on the tolerance mechanism.2. The results confirmed that poor light stress didn't cause obviously harm to PS II system and the leaf area accumulation may also sever as an indicator to evaluation the adaptability of cucumber cultivars to poor light .The poor light was the dominant stress factor when accompanied with lower temperature. However, the critical low temperature was the dominant stress factor when accompanied with poor lights. It was clear that the tolerance to poor lights was relative independent from the tolerance to low temperature .The treatment of low temperature and poor lights could induce the adaptability to critical low temperature stress and milden the chilling injury.3. Chilling injure index under critical low temperature and leaf area increase under poor light may act as reliable and reproductive evaluation index for low temperature and low light tolerance in cucumber. In this paper, an evaluation system of tolerance to low light and critical low temperature was designed by using the two indexes.4. Tolerance ability of low temperature and poor light was evaluation in 117 recombinant inbred lines using the evaluation system established in this paper. For QTL detection, the interval mapping method was employed based on a molecular genetic map constructed with RAPD, AFLP arid SSR markers. Five putative QTL were mapped in three linkage groups. One locus showed positive additive effect, while four loci showed negative additive effect. These results will provide the possibility for using molecular marker assistant selection in transferring the poor light adaptability from European greenhouse type to North China type.