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Amino acid composition and nutritional quality of potato leaf phloem sap for aphids

A. J. Karley^1,*, A. E. Douglas¹ and W. E. Parker²

¹ Department of Biology, University of York, Heslington, York, YO10 5YW, UK
² ADAS Woodthorne, Wergs Road, Wolverhampton, WV6 8TQ, UK

View larger version (21K): [in a new window]   Fig. 1. (A) Mean dry mass of above-ground (stems, leaves, flowers/berries) and below-ground (roots, tubers, stolons) plant parts measured in potato plants grown under glass. The broken line indicates the switch in dry-matter partitioning (see text for explanation). Values are the means ± S.E.M. of ten plants. (B) Ratio of carbon to nitrogen (C:N) (as percentage of dry mass) in dried leaf tissue and the molar ratio of sucrose to amino acid (sucrose:amino acid) in leaflet phloem exudates sampled from potato plants grown under glass. Values are the means ± S.E.M., N=9-10.

View larger version (13K): [in a new window]   Fig. 2. Principal component analysis of amino acid mol% data in leaf phloem exudates sampled from potato plants grown under glass during sequential stages of plant development: `pre-tuber filling' and `tuber filling' (see text and Fig. 1 for explanation). (A) Attribute loadings on the first two components PC 1 and PC 2. Amino acid abbreviations are denoted in Table 1. (B) Plot of the sample scores on PC 1 and PC 2 which explain, respectively, 38.0% and 13.2% of the variation in the dataset.

View larger version (25K): [in a new window]   Fig. 3. Variation in (A) the relative growth rate (RGR) and (B) the estimated intrinsic rate of population increase (Rm) of aphids developing from offspring raised on `young' and `old' diets (circles) and for `pre-tuber-filling' and `tuber-filling' plants (squares). Values are either the mean RGR ± S.E.M. (N=8-15) or the mean Rm ± S.E.M. (N=7-14) for clones of Myzus persicae (open symbols) or Macrosiphum euphorbiae (closed symbols). Points falling below the line of equivalence indicate clones that perform better on the `young' diet. *Clones showing a significant difference, in post-hoc analysis, between `young' and `old' diets. ANOVA for RGR: diet: F1,129=13.57, P<0.001; species: F1,129=10.72, P<0.05; interaction: F1,129=0.37, P>0.05; clone (subspecies): F4,129=5.60, P<0.001. ANOVA for Rm: diet: F1,120=31.95, P<0.001; species: F1,120=37.87, P<0.001; interaction: F1,120=1.43, P>0.05; clone (subspecies): F4,120=4.75, P<0.01.

View larger version (14K): [in a new window]   Fig. 4. Feeding rate on radiolabelled `young' and `old' diets by three clones of Myzus persicae. Values are the means ± S.E.M. (N=15-20). Analysis of covariance (ANCOVA) after log-transformation of feeding rate: aphid protein content (covariate): F1,111=9.31, P<0.05; diet: F1,111=33.86, P<0.05; clone: F2,111=52.90, P<0.05; interaction: F2,111=1.09, P>0.1. *Significant difference between diets (two-sample t-test of log-transformed data: ADAS 99/13, RB/4158; or Mann—Whitney U-test of untransformed data: ADAS 99/12) using Bonferroni correction for multiple tests.