Evaluation of nitrogen fertilization effect on apple-tree leaves and fruit by fluorescence imaging

The work aims to validate the laser-induced fluorescence imaging method for detecting nutrient deficiency of fruit- trees and testing the storage ability of the fruits. Measurements concerned apple-trees (Malus x domestica Borkh.cv.Jonagold 2361) submitted or not to nitrogen fertilization (60 kg/ha) via roots. Besides recordings of fluorescence images of fruits and of leaves at the characteristic emission wavelengths, images which always showed an effect of the nitrogen, chemical and physiological analysis have been performed. The essential results were: (1) For rosette leaves, with a total chlorophyll content significantly lower for nitrogen depleted leaves, and a Chl a/b ratio as well as (phi) po (PS II efficiency of open reaction centers) independent of the treatment, images recorded in the red and in the far-red (690 and 740 nm chlorophyll a emissions) showed red/far-red intensities ratios higher in the absence of fertilization, in agreement with the lower chlorophyll a content. (2) For leaves of one year shoots, having all similar chlorophyll content and PS II efficiency, nitrogen supply led to a slight decrease of the red/far-red ratio value for 532 nm excitation, and for 355 nm excitation to an important decrease of the blue fluorescence/chlorophyll emission ratio, that was not observed for rosette leaves. (3) For apple fruits, presenting a high K/Ca ratio (approximately equals 42) i.e. a bad storage ability, the chlorophylls content of the green face skin as well as (phi) po were the same for both samplings, with a dramatic decrease of (phi) po (0.68 till to 0.45) during conservation (6 months). Under 355 nm excitation, the fluorescence ratios the most sensitive to the nitrogen deficiency were for the green face the blue/red ratios which decreased with nitrogen supply and increased with time, and the blue/green ratio for the apple red face.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.