The study of the mechanisms that modify the chlorophyll fluorescence emission can be used to characterize the physiological behaviour of plants as affected by mineral deficiencies or excesses. The aim of this paper was to carry out a preliminary study of the application of chlorophyll fluorescence as an alternative for identifying iron and manganese deficiencies in peach tree leaves under field growing conditions. For this purpose in a peach tree orchard leaf samples (control, Fe deficient and Mn deficient) were taken from the basal (old) and apical (young) part of the shoots. The samples were analyzed for Mn, Fe, and photosynthetic pigments. Modulated fluorescence and kinetics of fluorescence were recorded in the sampled material. Both manganese and iron deficiencies decreased variable chlorophyll fluorescence (Fv). Iron deficient leaves showed low Fv/Fp (≈0.77) and Fv/Fm (≈0.70) ratios as evidence of diminished PS II photochemistry. However, old manganese deficient leaves provided the same Fv/Fp (≈0.78) ratio as controls, while manganese deficiency in young leaves produced high Fo, which indicates a greater extent of antenna versus PS II reaction centers. From these findings a derived consequence has been obtained: It may be possible to detect subclinical manganese deficiencies in the field, that is to say, before visual symptoms have developed.

This paper was supported by projects PCA 4/91 and 6191 (Research Advisory Board. Diputación General de Aragón) and AGR9O-0792 (National Plan for Agricultural Research).

9 Pags.- 3 Tabls. The definitive version is available at: http://www.actahort.org/index.htm

Peer reviewed