Effects of different bud dormancy breaking treatments on winter bud germination in Shine Muscat grapevines

Abstract：【Objective】This study aimed to find an ideal and effective bud dormancy break method for Shine Muscat grapevines and to explore the gene expression level of bud dormancy break by using H2CN2 and“lime sulfur mixture+ACC”.【Methods】By using the winter buds on Shine Muscat grapevines as materials, we studied the effects of different bud dormancy breaking treatments in the endodormancy stage and paradormancy stage on germination rate, flowering rate and inflorescence quality, and examined the possible effects on grape winter buds through transcriptome sequencing, and the key genes that may affect grape winter bud germination were screened through transcriptome sequencing. 【Results】The winter buds on the isolated canes of the Shine Muscat grape at the endodormancy stage were treated with cyanamide (T1) and“lime sulfur mixture+ACC”(T2) at one month before germination stage. The results showed that with T1 treatment grapevines sprouted earliest, followed by T2 treatment, and finally was the control (CK). The overall germination speed of each treatment showed a trend of“first-slow-and-then-fast”. In terms of germination rate, the germination rate with T2 treatment was the highest at 85.80% , followed by T1 treatment and CK, with germination rates being 81.48% and 66.05%, respectively. And the germination rates after T1 treatment and T2 treatment were significantly higher than those of the CK. The growth and development dynamics of winter buds on isolated canes were observed, and it was found that the winter buds treated with T1 and T2 all grew 2 to 3 new leaves on March 21, 2022. T1 treatment sprouted the earliest, and T1 and T2 sprouted more neatly; In the Con-trol group, 2 to 3 new leaves grew on April 2, 2022, and the growth was relatively slow and the sprouts were irregular. In August 2022, cyanamide treatment (H2CN2, T1) and“lime sulfur mixture+ACC”treatment (T2) was carried out on the winter buds of Shine Muscat grapevines at the paradormancy stage, and the results showed that with T1 treatment, grapevines sprouted earliest, followed by the CK and T2 treatment. The germination speed with each treatment showed a trend of“first-slow-and-then-fast”as well. The germination rate of T2 treatment was the highest, which was 69.70%, followed by T1 treatment and CK group, with germination rates being 65.66% and 41.41%, respectively. The germination rate of T1 and T2 treatment was significantly higher than that of the CK group. In February 2023, by treating the winter buds of Shine Muscat grapevines at the endodormancy stage with cyanamide (T1) and“lime sulfur mixture+ACC”(T2), the results showed that the T2 treatment had the highest germination rate of 97.22%, followed by T1 treatment and CK group, with the germination rates being 96.43% and 76.19%, respectively. From 25 days after treatment to the end of counts, the germination rate of T1 and T2 treatments showed significantly higher level than the CK. There was no significant difference in the inflorescence rate between T1 and T2 treatments, and CK. Simultaneously, the length of inflorescence was not influenced as well. The growth status of the canes was observed, and the results showed that, compared with the CK, the leaves grew fastest after the T1 treatment on April 3, 2023, followed by T2 treatment. On April 29, 2023, the leaf growth rate, leaf size, and internode length after T1 and T2 treatments had no significant impact compared with the CK. Six samples at the endodormancy stage (winter buds were collected at 24 h and 72 h after CK, T1 treatment and T2 treatment) and six samples at the paradormancy stage (CK, T1 treatment and T2 treatment were collected at 24 h and 72 h after winter bud) for transcriptome analysis, a total of 4399 differentially expressed genes were obtained by using |log2fold changes| ≥1, FDR＜0.01 as the filtering parameters, and 4399 significantly different genes (DEGs) can be divided into 8 clustering groups. Among all the DEGs, in W-CK-72 samples and W-HC-72 samples at the endodormancy stage, 10 genes were annotated as transcription factor coding genes, which were all related to bud germination. The transcription factors of them were up- regulated and 7 transcription factors were up-regulated. In addition, 10 genes were annotated as being involved in the biosynthesis or signal transduction processes of hormones such as auxin, gibberellins, abscisic acid and brassinosteroids. Five genes were related to the ABA signaling pathway, and among them, PYL4 and PP2C25 genes showed up- regulated expression, while PP2C24, PP2C8 and PP2C37 genes had down-regulated expression. The SAPK2 gene that related to the Snrk2 family was down regulated. The remaining differential genes screened were related to oxidative stress, glutathione S- transferase, etc. These candidate genes may affect grape bud germination by participating in hormone signaling, oxidative stress and other pathways.【Conclusion】The mixed solution of“lime sulfur mixture+ACC”is a safe and effective agent for breaking the bud dormancy of Shine Muscat grapevines. Genes involved in hormone signaling and oxidative stress may respond to the dormancy release process.