Germplasm Identification Of Tolerance To Low Temperature And QTL Mapping For Low Temperature Adapbility In Cucumber

Cucumber is one of the most important thermophilic vegetables in our country. The totalproduction in China mainland has reached48million ton, ranking first in the world. The yield andquality of cucumber are often influenced by chilling injury in early spring and in winter. Therefore,researches of tolerance to low temperature have been one of the hotpots in crops. In this study, the coldtolerance of15materials at germination and seedling stage under different low temperatures wascompared systematically in order to construct optimum evaluation method for the identification ofcucumber germplasm resources. In addition, the tolerance to low-temperature at the stage ofgermination for66core gemplasms was identified and evaluated to obtain different kinds materialstolerant to low temperature. Furthermore, F2population with parents showing obvious difference in coldtolerance was constructed. SSR and InDel makers were used to construct a molecular linkage map. QTLmapping was performed with the method of F2phenotype values estimated by F3determinations. Aboveresults will improve the exploration of elite genes of tolerance to low temperature and gerplasmenhancement. The main results were as followed:1. The cold tolerance of15materials were identified under13℃and15℃（CK:26℃）respectively,using six indexes including relative germination percentage, relative germination power, relativegermination index, relative radicle length, relative fresh weight and relative dry weight. The resultsshowed that13℃was better to be used for the screening materials with a strong tolerance to lowtemperature while15℃was more suitable for cold tolerance evaluation of cucumber germplasmresources. The different treated days under6℃at the stage of seedlings for15materials were identifiedand compared. The suitable treatment was4～5days if using injury index while3～4days for recoveryindex. Under15/5℃, the fitted treatment were13～15days for injury index while11～13days forrecovery index.2. A total of66core germplasms were identified and evaluated under15℃at the stage ofgermination. The results showed that the range of relative germination percentage, relative germinationpower, relative germination index, relative radicle length, relative fresh weight and relative dry weightwere1～123%,0～112%,0～70%,13～109%,0～100%,0～101%respectively, showing that theseeds vigor and growth ability of most materials were influenced by low temperature and just some ofthem expressed no obvious difference comparing with CK.7accessions with extremely high tolerancewere screened out.3. JD32with high tolerance to low temperature and QT193sensitive to low temperature were usedto construct F2population.126polymorphic markers were screened out among830SSR markers and134InDel markers. A linkage map including7groups was constructed, including68SSR makers and7InDel markers. It covered approximately908.9cM of cucumber genome with an average geneticdistance of12.28cM, the number of markers on each chromosome varies from2to25, with the lengthfrom21.2cM to190.3cM. 4. Using a LOD threshold of2.5,4QTLs related with cold tolerance were screened out. Amongthem, qCT-3-1, qCT-3-2, qCT-3-3related with chilling injury index were on chromosome3,accumulated phenotypic contribution rate of them was14.4%. The qCT-7-1with recovery index was onchromosome7, the variance of it was3.7%. In addition,5QTLs related with fruit color and1QTLrelated with fruit spine density were mapped on chromosome3and on chromosome6.