Comprehensive evaluation and palynological cluster analysis of introduced peony cultivars in Jiangnan region

Objective This study aimed to conduct a comprehensive evaluation of introduced peony cultivars in Jiangnan region and analyze the genetic relationships among the introduced cultivars， so as to provide a theoretical basis for breeding peony cultivars adapted to local conditions.Method Field investigations on 33 introduced peony cultivars in the Jiangnan region were conducted using the analytic hierarchy process （AHP）. The 33 introduced peony cultivars were evaluated from the perspective of ornamental value， growth traits， ecological adaptability and so on to establish a comprehensive evaluation system for screening peony cultivars of high-adaptability. Concomitantly， pollen morphology was observed， and cluster analysis was performed to determine genetic relationships among the cultivars.Result Based on the characteristics of peonies， a four-tiered hierarchical model was established， comprising the target layer， constraint layer， criterion layer， and base layer. By incorporating ornamental value， growth traits， and ecological adaptability as comprehensive evaluation factors， an evaluation model for introduced peonies. In the criterion layer， the weight value of growth traits was the highest （0.5813）， while in the factor layer， the weight value of branch number was the highest （0.4960）. The evaluated cultivars were classified into four grades based on comprehensive assessment scores： GradeⅠ， Grade Ⅱ， Grade Ⅲ， and Grade Ⅳ. Three cultivars were rated as excellent cultivars in GradeⅠ： Xiangxiuqiu， Daojin and Linfeng； nine cultivars were rated as good cultivars in Grade Ⅱ； eighteen were rated as average cultivars in Grade Ⅲ； and three were rated as poor cultivars in Grade Ⅳ： Haihuang， Taiyang and Xinyungu. Scanning electron microscopy revealed that the pollen of 33 introduced peony cultivars occurred as single grains， most of which were prolate spheroidal （polar axis/equatorial axis > 2.00）. In polar view， the pollen grains appeared trilobate-rounded， with three colporate germinal apertures， and the exine ornamentation was predominantly foveolate-reticulate. Cluster analysis based on quantitative indicators of pollen morphological characteristics revealed significant diversity in exine ornamentation patterns among the introduced tree peony cultivars. At a Euclidean genetic distance threshold of 1.5， the cultivars were classified into five groups： Group Ⅰwith 23 cultivars， Group Ⅱ with 2 cultivars， Group Ⅲ with 6 cultivars， and Groups IV and V each with one cultivar. At a Euclidean genetic distance threshold of 5.0， the cultivars were classified into two groups： Group A with 31 cultivars （including GroupⅠ-Ⅲ）， and Cluster B with 2 cultivars （including Group Ⅳ-Ⅴ）.Conclusion When introducing peony in Jiangnan region， the priority is considering growth traits， followed by adaptability and ornamental value. GradeⅠcultivars， Xiang Xiuqiu， Dao Jin and Lin Feng， are recommended for large-scale introduction as principal varieties. Grade Ⅱ cultivars with relatively good performance can be introduced based on demand， while Grade Ⅲ and Ⅳ cultivars with unsatisfactory performance and are not recommended for introduction. Among the introduced peony cultivars， Haihuang and Rimu are distantly related to the other cultivars， whereas Shouanhong and Fengdanlan are closely related.