Compensation effects in grape phylloxera (Daktulosphaira vitifolia Fitch)infested vines on root growth, leaf respiration and sink activity
Abstract: Symptoms of grape phylloxera (Daktulosphaira vitifoliae Fitch, Phylloxeridae) infestation on susceptible and partially resistant rootstocks of vines in the field rarely show severe plant damage. Nevertheless grape phylloxera induces root galls on tips of susceptible and partially resistant rootstock cultivars affecting the host physiology by inhibition of water and mineral uptake and sink-source translocation. Phylloxera root galls were shown to represent novel sink organs accumulating high levels of carbohydrates and amino acids withdrawn from the plant primary metabolism. In our research we aim to analyse to what extent the host physiology is affected by carbohydrate competition and whether phylloxerated vines respond with a compensation strategy comprising increased root growth and respiration activity in non-infested roots of phylloxerated vines. Two experiments were designed: Experiment 1 was performed with potted two year old grafted grapevines (V. vinifera L. ‘Pinot Noir’ on SO4 (V. berlandieri x V. riparia)) cultivated in two isolated climate chambers. Treatments differed by with/without clusters. Photosynthetic activity and gas exchange, vegetative and phenological development were measured. Fresh/dry weight and berry parameters were determined destructively. Experiment 2 was performed with double eye cuttings of the rootstock Teleki 5C (V. berlandieri x V. riparia) in greenhouse conditions. Phylloxera eggs derived from an identical phylloxera strain (biotype C). The results demonstrated that belowground root mass was increased upon phylloxeration. Phylloxerated root galls and non-infested root tips of phylloxerated vines accumulated increased amounts of nitrogen and carbon underlining the increased sink strength of the root system. Gas exchange rates were elevated upon root phylloxeration indicating an increased metabolic activity and elevated carbon fixation rate in the leaves. However photosynthetic efficiency was not found to be explicitly modified. Decreased levels of P and K were detected in phylloxerated root galls and might be explained by a dilution effect due to increased import of carbohydrates and amino acids and/or by the dysfunctionality of the transformed root tips to galls.