Effect of Temperature Regimen at the Seedling Stage of Primula obconica on Primin Secretion

Abstract

Primula obconica Hance secrets primin which causes allergic-dermatitis, and seedling test of primin is important for breeding primin-free cultivars. To be able to select primin-free Primula obconica at their seedling stage, plants grown under different temperature were observed. 1. Primin secretion began in the cotyledonary stage in 'Crystal Apricot' seedlings. 2. When 'Crystal Apricot' seedlings were grown under either low (20/13 °C) or high (30/23 °C) (day/night) temperature, all seedlings secreted primin at the 1st leaf expanding stage under 20/13 °C. Furthermore, the primin secreting percentege of the leaves at lower nodes were consistently high under 20/13 °C. However, the onset of primin secretion was delayed at 30/23 °C, and it ceased earlier at 30/23 °C than it did at 20/13 °C. The percentage of primin-secreting leaves directly below the expanding apical leaf was higher than those of leaves at lower nodes independent of the ambient temperature. 3. The percentage of primin-secreting leaves directly below the expanding apical one in four 'Crystal' cultivars revealed difference among cultivars as to when the secretion began. Primin secreting percentage of all cultivars reached 100% in cotyledon as the first leaf was expanding at 20/13 °C, whereas it was the 4th leaf as the 5th-leaf was expanding at 30/23 °C. In conclusion, our results demonstrate that primin-free plants can be selected at the cotyledon as the first leaf was expanding by growing them at 20/13 °C or at the 4th leaf as the 5th-leaf was expanding at 30/23 °C.