Effects of different dwarfing interstocks on endogenous hormone and sugar contents in leaves of young Yanfu No. 3 apple trees

Abstract:【Objective】As the dwarf cultivation mode of apple becomes an inevitable trend, Yanfu No. 3 has been the main cultivar in Jingning area. In order to further screen out the most suitable stion combinations in Jingning area, the effects of different dwarfing interstocks on endogenous hormone and sugar contents in leaves of young Yanfu No.3 trees were investigated, so as to lay the foundation for further screening of the stion combinations suitable for the development in the Jingning area.【Methods】In this experiment, Yanfu No.3 was used as scion, Malus micromalus as the base rootstock, and M26, GM256, P16, P2, M27, T337, SH40, SH6 and M9 as the intermediate stocks. The trees were planted in 2017 and an investigation was made on tree height, shoot thickness, annual shoot length, internode length, leaf area and SPAD after shoot growth stopped in autumn of 2020. Then the leaves were collected and brought back to the laboratory to determine the contents of ZT, GA3, IAA, ABA, sucrose, fructose, glucose and sorbitol in the leaves. Three trees were selected from each scion/rootstock combination with three repli-cates, totaling for 81 trees. Correlation and significance analyses were used to screen out the most suitable combination of Yanfu No.3 and interstock.【Results】There were significant differences in tree growth among the 9 scion/rootstock combinations. As a dwarfing interstock, P16 had the lowest tree height, while M9 had the highest tree height. The change pattern of shoot diameter and internode length was basically consistent with tree height. The shoot diameter and internode length with P2 and P16 interstocks were the smallest among 9 rootstocks. The leaf areas with P2 and P16 were larger, and their SPAD values were also higher. The ZT content in leaves with P16 was 23.97 ng·g^-1 , which was significantly higher than that with other interstocks. The ZT content with P2 was significantly higher than that with other interstocks except P16, and the ZT content with P2 was 21.52% lower than that with P16. The GA3 content in leaves with M26 was significantly higher than that with other interstocks (13.63 ng·g^-1). The GA3 content in leaves with SH40 was the lowest (5.99 ng·g^-1 ), and the content with M26 was 2.27 times that with SH40. The IAA content in leaves with GM256 was significantly higher than that with other interstocks (149.25 ng·g^-1 ). The IAA contents with P2 and P16 were at a low level. The ABA content with P16 was 164.86 ng·g^-1 , which was 38.43% lower than that with P2. The ratio of IAA/ABA was consistent with the pattern of the ratio of (ZT+GA3+IAA)/ABA, with GM256 having the highest ratio and P2 having the lowest ratio. Combined with the analysis of tree growth indicators, the hormone ratio was relatively consistent with the tree growth pattern, i.e. the smaller the ratio of IAA/ABA to (ZT+GA3+IAA)/ABA, the more dwarfed the tree was, so P2 and P16 had the best dwarf ability, while SH40 and SH6 could result in more moderate trees. When P16 was used as the dwarfing interstock, the contents of fructose and glucose in leaves were the highest, while when SH40 or SH6 was used as the interstock, the contents of fructose and glucose in leaves were next only to P16. When T337 was used as the dwarf interstock, the contents of sorbitol and sucrose in leaves were the highest, and the sorbitol content in leaves with P2, P16, SH40 and SH6 was next only to that with T337, while the sucrose content was at a lower level. Correlation analysis showed that tree height was negatively correlated with glucose, ZT and ABA contents. The shoot diameter was negatively correlated with fructose, glucose, sorbitol and ABA contents. Internode length was significantly and negatively correlated with fructose, glucose and ABA contents, IAA/ABA and (ZT+IAA+GA3) /ABA ratios, and sucrose content. Correlation analysis showed that tree height, shoot diameter and internode length were negatively correlated with ABA content, indicating that tree growth was related to ABA content in leaves. Internode length was positively correlated with IAA/ABA and (ZT+IAA+GA3) /ABA ratios, indicating that tree growth was related to hormone content in scion leaves. Most of the sugar components in scion leaves were negatively correlated with tree growth index, indicating that sugar accumulation in scion leaves also affected tree dwarfing degree.【Conclusion】When P2 and P16 were used as dwarfing interstocks of Yanfu No. 3, the tree growth was the lowest, and the ABA content in leaves was significantly higher than that in leaves with other interstocks. The ratio of IAA/ABA and (ZT+IAA+GA3) /ABA was the lowest, indicating that the dwarfing efficacy of P2 and P16 was the best among the 9 dwarfing interstocks. SH40 and SH6 were next only to P2 and P16 in terms of dwarfing, and the tree vigors were more moderate compared to P2 and P16, making them more suitable as dwarfing intermediate rootstocks for Yanfu No. 3 only in terms of tree vigor and dwarfing.