LPS‐induced chlorosis in chrysanthemum as influenced by genotype and ammonium/nitrate ratio

Abstract

The influence of ammonium/nitrate ratio on the chlorophyll content and induction of chlorosis under low‐pressure sodium (LPS)‐lamps was examined in two cultivars of Chrysanthemum morifoliurn Ramat. ('Mountain Snow’ and ‘Fiesta') found previously to differ in sensitivity to water stress. Plants were grown in a peat moss‐vermiculite mix under controlled environments for 39 days under LPS lamps at a photosynthetic photon flux of 320 umol s^‐1 m^‐2. Plants were fertilized twice daily with one of three complete nutrient solutions containing nitrogen at a NH₄/NO₃ ratio: of 0/100; 50/50; or 100/0. Significant differences in the severity and rate of development of chlorosis were observed depending upon the genotype and NH₄/NO₃ ratio. Drought‐tolerant ‘Fiesta’ showed little chlorosis after 39 days of treatment while drought‐sensitive ‘Mountain Snow’ exhibited marked bleaching of the leaves as the percentage of NH₄ in the solution increased. Bleaching appeared first in the youngest leaves on the main shoot and lateral shoots and proceeded basipetally. Increasing the NH₄/NO₃ ratio from 0/100 to 100/0 hastened the onset of chlorosis in the primary and secondary leaves of NH₄‐sensitive ‘Mountain Snow’ by 8–9 days. After 39 days, both cultivars displayed chlorosis, even at 100% NO₃, indicating that this damage was probably not caused by NH₄ treatment alone, but was enhanced by high NH₄. These findings thus demonstrate an interaction between spectral quality and NH₄ nutrition in growth chamber‐grown chrysanthemum.

Key words:

• Chrysanthemum morifolium Ramat.
• low pressure sodium lamps
• spectral quality
• NH₄ x radiation stress
• chlorophyll content
• genotype differences