Potential of Xiaoguo Tianshi and Niuyanshi (Diospyros kaki Thunb.) as novel rootstocks for PCNA persimmon

Abstract: 【Objective】Grafting is an ancient and now well-developed technique for persimmon produc⁃tion. However, some leading Pollination Constant Non- astringent (PCNA) persimmon cultivars like‘Fuyuu’or‘Taishuu’are early or late incompatible with Chinese traditional rootstock Date plum (Diospyros lotus L.). This incompatible phenomena may result in propagation failure in nursery or weak tree vigorin orchard. Therefore, it is important to survey and select widely-compatible rootstock for PCNA persimmon. Recently, two genotypes named Xiaoguo Tianshi and Niuyanshi were collected from the Dabieshanmountain region in central China. The aim of this study was to explore the genetic status and clarify the potential as extensive rootstock of Xiaoguo Tianshi and Niuyanshi before commercial use.【Methods】TheSSAP (sequence-specific amplification polymorphism) method based on LTR retrotransposon was utilizedto investigate the genetic relationship among Xiaoguo Tianshi, Niuyanshi and some persimmon cultivarsor species. The calculation of DICE similarity coefficient and clustering analysis were carried out by NT⁃SYS-PC version 2.10e software. In vitro culture and grafting techniques were applied for determining ear⁃ly characteristics of grafting compatibility using Xiaoguo Tianshi and Niuyanshi as rootstocks for PCNApersimmons. During grafting union formation, observation of growth and anatomical investigation of chang⁃es occurring in graft surface were made by using Nikon Eclipse E200 microscopy. Meanwhile, the fieldperformance of the 6 years old trees derived from the four grafting combinations including‘Matsumotowase’and‘Jirou’grafted onto Xiaoguo Tianshi and Niuyanshi repectively from 2012 to 2015 were ob⁃served to evaluate long-term effects of rootstock on scions in the fruiting season. The scion tree growthwas assessed through the measurement of trunk height, scion and rootstock circumference, fruit set percentage, fruit index, yield, fruit weight, seed number and soluble solid content (SSC). The software OriginPro8.1 was used for trees growth, yield and quality data analysis.【Results】(1) From 38 selected SSAPprimers, 29 primer sets exhibited robust amplification in these tested materials. In total, 442 scorable am⁃plification bands were generated by retrotransposon- based markers, accounting for 97.7% polymor⁃phisms. Based on UPGMA analysis, 26 Diospyros species and cultivars could be divided into 4 clusters.Cluster I comprised Chinese and Japanese cultivars, and Xiaoguo Tianshi and Niuyanshi grouped togetherwith D. kaki. D. oleifera and Jinzaoshi fell into the Cluster II. All the accessions of D. lotus formed a tightbranch Cluster III except for D. lotus T from Taiwan which presented a close relationship to D. glaucifolia (Cluster IV). (2) The examination of different callus-grafting combinations results showed homograftingwere more successful than heterografting. Histological observation of eight combinations showed that cellorganization and homogeneous arrangement on the grafting surface, strongly stained with Safranine andFast Green except for‘Fuyuu’/Date plum, in which graft surface with a portion of black area retained at35 DAG (day after grafting). Xiaoguo Tianshi and Niuyanshi as the rootstocks for‘Jirou’or‘Fuyuu’pre⁃sented a better callus formation than Date plum. Soluble tannin accumulated on the graft surface of‘Fuyuu’/Date plum resulted in the separating layer on the grafting surface and reduced survival of thegrafting. The growth and vascular anatomical investigation in 4 graft combinations of explanted internodegraftingat 15 DAG indicated that the homografting of‘Jirou’‘/ Jirou’would be the best combination, fol⁃lowed by Xiaoguo Tianshi and Niuyanshi as rootstocks. Meanwhile, there was a little vascular cambiumformation for differentiation in‘Jirou’‘/ Jirou’,‘Jirou’/Xiaoguo Tianshi. However, disorganized cell ar⁃rangement on the grafting surface of‘Jirou’/Date plum were noticed. 30 days after explanted internodegrafting,vascular regeneration was found in‘Jirou’/Xiaoguo Tianshi and‘Jirou’/Niuyanshi, each graftingcombination had healed apparently except for‘Jirou’/Date plum. These results indicated that vascular regeneration rate influenced the time of grafting union establishment among these grafting combinations.Grafting compatibility corresponded to the new callus formation rate and xylem connection. Polyphenolsoxidization on the grafting surface could influenced grafting compatibility. The early performance of in vitro scion/rootstock combination of‘Fuyuu’with Xiaoguo Tianshi and Niuyanshi werte remarkably betterthan that with Date plum. (3) The scion-rootstock ratio of‘Matsumoto-wase’/Niuyanshi was 0.99 whichwas higher than that around 0.9 in other 3 grafting combinations, indicating better compatibility of graftingunion between Niuyanshi and‘Matsumoto-wase’. Yield and fruit set percentage of the scion trees graftedon Niuyanshi tended to exceed those on Xiaoguo Tianshi. No significant effects of interaction between rootstocks and scions on fruit quality were found, which fluctuated in different years. These adult trees showednormal growth in the field. Niuyanshi and Xiaoguo Tianshi seems to be compatible with‘Jirou’and‘Matsumoto-wase’.【Conclusion】Those results suggested that Niuyanshi and Xiaoguo Tianshi belong to D. kaki and could be an excellent rootstock candidates for PCNA persimmon in China.