Impact of white mistletoe (Viscum album ssp. abietis) infection severity on morphology, anatomy and photosynthetic pigment content of the needles of cilicican fir (Abies cilicica)

Abstract

White mistletoe (Viscum album ssp. abietis, Santalaceae) is a hemi-parasitic plant and is regarded as one of the most significant biotic factors affecting fir forests. Mistletoe affects its host in many ways, including changes in leaf development. This paper studies and quantifies the effect of white mistletoe on morphological, anatomical traits and photosynthetic pigment content of cilicican fir (Abies cilicica (Antoine & Kotschy) Carrière, Pinaceae) needles growing on uninfected branches of infected and uninfected trees in relation to varying mistletoe infection severity. Morphological (needle length and width, area and weight, and specific leaf area), anatomical (needle width and thickness, epidermis and central vein thickness, needle cross sectional and mesophyll area, epidermis plus hypodermis and central vein area, xylem and phloem area, transfusion and resin duct area), stomatal (number of stomata rows, stomatal band width, stomata length and density) traits and photosynthetic pigment content (chlorophyll a and b, total chlorophyll (a+b), total carotenoid) were measured in one-year-old needles growing on uninfected branches from a total of 48 cilicican fir trees. Of the trees, 10 were uninfected, 13 lightly infected, 14 moderately infected and 11 severely infected. The results indicated that morphological dimension of needles decreased steadily with increasing infection severity. Stomatal size of needles decreased gradually while stomatal density increased gradually with increasing infection severity. Reduced anatomical dimension were only evident in needles from moderate and severe infection classes, while chlorophyll content decreased in only severely infected trees.