Effect of temperature regimen at the seedling stage of Primula obconica onprimin secretion

Primula obconica Hance secrets primin which causes allergic- dermatitis, an d 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' se edlings. 2. When 'Crystal Apricot' seedlings were grown under either low (20/13 degr eesC) or high (30/23 degreesC) (day/night) temperature, all seedlings secre ted primin at the Ist leaf expanding stage under 20/13 degreesC. Furthermor e, the primin secreting percentege of the leaves at lower nodes were consis tently high under 20/13 degreesC. However, the onset of primin secretion wa s delayed at 30/23 degreesC, and it ceased earlier at 30/23 degreesC than i t did at 20/13 degreesC. The percentage of primin-secreting leaves directly below the expanding apical leaf was higher than those of leaves at lower n odes independent of the ambient temperature. 3. The percentage of primin-secreting leaves directly below the expanding a pical one in four 'Crystal' cultivars revealed difference among cultivars a s to when the secretion began, Primin secreting percentage of all cultivars reached 100% in cotyledon as the first leaf was expanding at 20/13 degrees C, whereas it was the 4th leaf as the 5th - leaf was expanding at 30/23 deg reesC. In conclusion, our results demonstrate that primin- free plants can be sele cted at the cotyledon as the first leaf was expanding by growing them at 20 /13 degreesC or at the 4th leaf as the 5th- leaf was expanding at 30/23 deg reesC.