Evaluation and screening of dwarfing ‘Duli’ (Pyrus betulifolia Bunge) seedlings by principal component analysis and membership function analysis

Abstract

Dwarf and close planting are emerging as key strategies for pear cultivation, and dwarf ‘Duli’ (Pyrus betulifolia Bunge) rootstock is essential for the success of these planting strategies. However, dwarfism is a complex trait, and many factors influence dwarfism. To evaluate its dwarf characteristics and screen dwarf ‘Duli,’ 28 traits (growth, physiology, and gene expression levels) in 20 dwarf (D1–D20) and 1 control (A1) ‘Duli’ seedlings were subjected to principal component analysis (PCA) and membership function analysis. The results reveled variation in each index (9.14 %–69.66 %). The internode length, leaf area, and N–pathway enzyme (nitrate reductase, nitrous reductase, and glutamine synthetase) activity were significantly lower in D1–D20 than in A1 seedlings, and the chlorophyll content, photosynthesis, and abscisic acid (ABA) content were significantly higher in D1–D20 seedlings than in A1 seedlings. The expression levels of gibberellin (GA) synthesis pathway genes (PbGA3ox2) and N pathway genes (PbNRT2.1, PbNIR, and PbGS2.2) were down-regulated. Correlation analysis showed that ABA and PbGAI1a were negatively correlated with plant length. Furthermore, the 28 indexes were reduced to six principal components by PCA. Based on the membership function, a comprehensive evaluation formula was generated; 20 dwarf seedlings could be divided into four categories according to the comprehensive scores, and D7 and D3 were extremely short seedlings. The results of our study will facilitate comprehensive evaluations of dwarf plants and have implications for ‘Duli’ breeding programs.