Effects of chilling requirement and chilling duration on the expression of bud dormancy-related genes in different grape rootstock varieties

【Objective】This study aimed to investigate the effects of chilling requirement and chilling duration on the expression of bud dormancy-related genes in different grape rootstock varieties，providing theoretical basis for screening low-chilling rootstock varieties suitable for tropical and subtropical regions and exploring the regulatory mechanisms of grape germination.【Method】Winter pruning bud-wood of 15 grape rootstock varieties were used as test materials，and subjected to different chilling duration treatments at（4±1）℃. The chilling requirement of each grape rootstock variety was detected，and the germination process was recorded. The changes of total soluble sugar and starch content in branches with different chilling requirements were analyzed during dormancy release induced by chilling requirement. The relative expression levels of dormancy-related genes in the buds were determined using real-time fluorescence quantitative PCR. 【Result】The chilling requirement of 12 grape varieties including Bayda，SO4，101-14，110R，188-08，3309C，140R， Valliant，Shanhe No. 2，BR No. 2，Fercal and 5C was 0 h，while the chilling requirement of 1103P was 168 h. The total soluble sugar content in the branches of 1103P rootstocks increased significantly with chilling duration added（P<0.05， the same below），reaching a maximum of 2.55 μg/g at 304 h of chilling duration，and the starch content in branches decreased significantly to 0.06 μg/g. In contrast，there was no significant difference in starch content in branches of 3309 C with low chilling requirement among the three chilling duration treatments（P0.05，the same below）. With increasing chillinng duration treatment，the relative expression of VvCALLOSE SYNTHASE1 in 1103P decreased significantly. The relative expression of callosal synthase gene VvCALLOSE SYNTHASE1 in 1103P winter buds without chilling treatment was significantly higher than that in 3309C. Among the three chilling duration treatments，the relative expression levels of β -1, 3-glucanase gene VvGLU1，ABA synthesis key enzyme gene VvNCED1，GA20-oxidase gene VvGA20ox-2，key transcription factor gene responding to cold stress VvbHLH92 and flowering inhibitory gene VvSVP in 1103P buds were the highest at 304 h of chilling treatment. In 3309C which did not enter endodormancy，the relative expression levels of VvCALLOSE SYNTHASE1 and VvSVP genes did not change significantly. The relative expression levels of VvGLU1 gene，ABA biosynthesis inducer VvXERICO gene and VvbHLH92 in 3309C buds were the highest without chilling treatment. The relative expression of VvSVP gene in 1103P buds was significantly higher than that in 3309C under all three chilling duration treatments.【Conclusion】The twelve grape rootstock varieties，including Bayda，SO4，101-14， 110R，188-08，3309C，140R，Valliant，Shanhe No. 2，BR No. 2，Fercal and 5C，are identified as rootstock varieties not requiring chilling requirement for germination. Grape germination is co-regulated by chilling requirement，nutrients and dormancy-related genes.