Changes in photosynthetic biomass accumulation, auxin and ethylene level following defoliation in Brassica juncea

Author: N. A. Khan

Received 11 January 2003, accepted 27 July 2003.

Abstract

The response of mustard (Brassica juncea L. Czern & Coss.) cvs. Alankar, PBM16 and Varuna to 0 (control), 15, 30 and 45% defoliation of shaded leaves in the lower canopy at 40 d after sowing (pre-flowering stage) was studied. The characteristics studied at 0 (pre-flowering), 30 (pod-initiation) and 60 d (pod-fill) after defoliation were leaf number, leaf area, photosynthesis rate, plant biomass, auxin concentration, IAA oxidase, total phenolics and ethylene evolution. The compensation of growth and plant biomass were greatest after removal of 30% of the shaded leaves in the lower canopy. Both leaf area and leaf number were increased after defoliation. Rates of leaf photosynthesis were not affected by defoliation treatments. Compensatory growth after defoliation was associated with increased IAA oxidase content, reduced auxin content, increased total phenolics levels and higher rates of ethylene release. The results suggest that efforts should be focussed on strategies that lead to the loss of lower leaves in canopy, which remains shaded and do not contribute significantly to photosynthesis and plant biomass.