Development of a Seedling Screening Method for Low-Temperature Tolerance in Pumpkin (Cucurbita moschata) and Selection of the Tolerant Resources for Rootstock of Cucumber

Pumpkin (Cucurbita moschata) has been increasingly used as bloomless rootstock for cucumber (Cucumis sativus), butit is sensitive to low-temperature, which is the major bottleneck for winter cultivation. Hence, to develop low-temperature tolerantrootstock varieties, it is needed to identify tolerant germplasm from a wide range of genetic resources. For this, we developed a selectioncriterion for a quick assessment of low-temperature tolerance in pumpkin germplasms from different geographical origins. Weconsidered various indexes for the fast evaluation of low-temperature tolerance, including seedling developmental stage, type ofseedling (excised or non-excised), growth space, etc. Under the testing condition (17℃/7℃, 8 hours light/16 hours dark, 150 μmol m-2s-1light intensity), we found a correlation (r=0.71*) in root growth between 3 weeks-cultured excised seedlings and 6 weeks-culturednon-excised seedlings. Therefore, we extrapolate that excised cotyledonary stage seedling treated for 3 weeks is sufficient todifferentiate the tolerant germplasms. Using this screening method, we identified the “S81015” could prevail low-temperature stress. Further, we tested grafting compatibility and growth of grafted cucumbers under the low-temperature condition to assess the effect ofrootstock and identify low-temperature tolerant and grafting-compatible rootstock germplasm. Upon grafting, we found a highcorrelation (r=0.97**) between the root fresh weight of 6 weeks-cultured non-excised seedlings and the shoot fresh weight of thegrafted cucumbers. In summary, we could identify the low-temperature tolerant pumpkin germplasms by screening at the earlydevelopmental stage. Further, as a rootstock, the tolerant pumpkins also fortified the low-temperature tolerance of grafted cucumbers.