Improving crucial details and selecting the optimal model for evaluating the chilling requirement of Paeonia lactiflora Pall. at low latitudes during four winters

Abstract

The countless perennial plants face severe problems associated with insufficient chilling accumulation and obstacles to dormancy release in warm-winter climates as a result of increased global warming. These problems hinder the ability of these plants to grow in low-latitude regions and consequently reduce their economic values. “The southward planting of herbaceous peony” (Paeonia lactiflora Pall.) is a representative example of promoting the expansion of temperate plants into subtropical and even tropical regions. Evaluating the chilling requirement (CR) of herbaceous peony and then selecting or breeding new cultivars that have substantial low-CR traits are important for peony cultivation and popularization at low latitudes. In this study, natural and controlled chilling treatments and CR evaluations were conducted for the southernmost cultivated Chinese peony, ‘Hang Baishao’, initially during three winters. The start times of the evaluations and the assessment criteria for the CR fulfillments were specifically defined, after which five models were used to evaluate the CR of ‘Hang Baishao’. According to the stability of the CR value during the three years, the availability of overlaps among the three-year CR ranges, and the correlations between the CR values and the morphological data, the Utah (UT) model was identified as the optimal model and was subsequently used to evaluate five other northern peony cultivars. The results indicate that ‘Hang Baishao’ and ‘Qihua Lushuang’ were representative cultivars with a low CR, while ‘Zhuguang’ represented a typical cultivar with a high CR. The dependability of the UT model was further confirmed by evaluating the CR of ‘Hang Baishao’ and ‘Zhuguang’ during a fourth winter. This study constitutes an integrated research strategy on CRs on the basis of multiyear observations, multi-treatment experiments, multi-detail definitions and multi-cultivar validations, and the results could provide new perspectives for studies on economic plants that undergo winter dormancy in low-latitude regions.