Effects of pollinizer cultivars on the morphogenesis and development of Yatu and the endogenous hormone content in the base of young fruit of ‘Yali’pear (Pyrus bretschneideri Rehd.)

Abstract【: Objective】‘Yali’(Pyrus bretschneideri Rehd.) is native to the Hebei province in China. It is one of the superior traditional pear cultivars. Yatu, formed on the stalk cavity of the fruit, is a typical phenotypic trait of‘Yali’. The existence and types of Yatu are important indicators for evaluating the quality of pears. Disappearance of Yatu frequently occurs in‘Yali’production, and the mechanism is unclear yet. It is important and necessary to clarify the mechanism of Yatu morphogenesis and develop- ment. Based on our previous studies, three pollinizer cultivars which had the different influence on Yatu formation were selected to perform controlled pollination for‘Yali’. This study aimed to explore the factors influencing the morphogenesis and development of Yatu【. Methods】The experiment was carried out from 2016 to 2017 in a commercial pear orchard in Botou, Hebei province, China (38°8′24′′ N, 116° 31′12′′ E).‘Yali’trees on P. betulaefolia Bunge rootstocks were planted in 1988 with a spacing at 4 m× 6 m and a north-to-south row orientation. The experiment was designed in a randomized blocks with three replications of two trees each. The first-order flowers within the inflorescence were bagged, and the others within the same inflorescence were removed 2 days before bloom. Then, during bloom, con- trol pollination was performed on the bagged flowers with the prepared pollens of‘Cuili’‘, Kuerlexian- gli’and‘Xuehuali’pears. The pollen of‘Cuili’, a native pear variety, was obtained from a local or- chard. The pollens of‘Kuerlexiangli’pear and‘Xuehuali’were obtained from the pear variety preser- vation garden in Zhaoxian, Hebei province, China. Mature fruit were harvested at 162 days after pollina- tion (DAP). The percentage of fruit with different types of Yatu were counted at 162 DAP. The differ- ence in fruit length between the two opposing sides of a fruit was used as a grading standard for Yatu. One side of the fruit with Yatu was marked by H, and the opposite side was marked by h. The classifica- tion of Yatu was determined by the difference between H and h (e.g., H-h). Fruit with a difference great- er than 2 mm were identified as the one with Yatu. We classified Yatu into two types based on the value of H-h: small Yatu (2 mm < H-h ˂ 5 mm) and typical Yatu (H-h ≥5 mm). The distance between the cut- ting point to the stalk cavity was 1/5 the length of the young fruit, and the base of the fruit was sampled. Samples were collected at 10, 20, and 35 DAP for hormone content determination. Thirty young pear fruit of each treatment were randomly collected, transferred to the lab on ice, sampled as above, ground to powder in liquid nitrogen and stored at - 80°C before being used to measure the hormone content. The hormones were determined by an enzyme-linked immune sorbent assay. The test was replicated three times for each treatment. Three technical replications were run for each biological replication in hormone analysis. The Date Processing System (DPS®) software was used to analyze the data. The significance of differences among means were determined by Duncan’s multiple range test ( p ≤ 0.05) us- ing Least Significant Ranges means.【Results】The controlled pollination with different pollination culti- vars significantly influenced the percentage and the types of Yatu. With the pollination by‘Cuili’and‘Kuerlexiangli’pears, the percent of fruit with Yatu was 100%, 84.9% (Year 2016) and 99.8%, 100% (Year 2017), respectively, which was significantly higher than 66.7% (Year 2016) and 60.7% (Year 2017) in pollination with‘Xuhuali’pollen. The percent of the typical Yatu in the fruit pollinated by‘Cuili’were 95.4% (Year 2016) and 92.2% (Year 2017), which were significantly higher than those pollinated by‘Kuerlexiangli’pear [54.2% (Year 2016) and 63.5% (Year 2017)] and‘Xuehuali’[46.7% (Year 2016) and 50.0% (Year 2017)]. In the early stage of young fruit development, the fruit pollinated by‘Cuili’and‘Kuerlexiangli’pear had significantly higher GA3 and ZR contents, lower ABA content, and less difference in IAA content compared to the fruit pollinated by‘Xuehuali’.‘Cuili’as pollinizer appeared to have the strongest effect to increase the contents of promoting growth hormones and to de- crease the content of ABA.【Conclusion】The different pollinizer cultivars influenced the percentage and types of Yatu. The morphogenesis and development of Yatu was regulated by the endogenous hormone balance. The relatively higher GA3 and ZR content and lower ABA content promoted the morpho- genesis and development of Yatu.