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Limitation to Photosynthesis in Pratylenchus penetrans- and Verticillium dahliae-Infected Potato


This article in CS

  1. Vol. 39 No. 5, p. 1340-1346
    Received: Oct 27, 1998

    * Corresponding author(s): macguid@macc.wisc.edu
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  1. I.A.M. Saeeda,
  2. A.E. MacGuidwin *a,
  3. D.I. Rousea and
  4. T.D. Sharkeyb
  1. a Department of Plant Pathology, 1630 Linden Dr., University of Wisconsin, Madison, WI 53706 USA
    b Dep. of Botany, University of Wisconsin, Madison, WI 53706 USA


Mechanism(s) responsible for decrease in photosynthetic rates of potato (Solanum tuberosum L.) leaves infected by the fungus Verticillium dahliae (Kleb) and the nematode Pratylenchus penetrans (Cobb, Sher, Allen) have not been fully researched. Two growth chamber experiments were undertaken to determine the factors contributing to the decrease in CO2 exchange rates of young, fully expanded leaflets of potato (cv. Russet Burbank) plants grown in pots infested with P. penetrans and/or V. dahliae Treatments were P. penetrans-infested soil, V. dahliae-infested soil, soil infested with both the nematode and the fungus, and a noninfested control. Leaf CO2 response curves were measured at early (16 d after inoculation [DAI]) and late (42 DAI) stages of infection for all treatments at saturating light (1500 μmol m−2 s−1 of photosynthetically active radiation [PAR] using a portable photosynthesis system. Carbon dioxide exchange rates were also measured at 1000, 400, and 200 μmol m−2 s−1 PAR to determine leaf light response. At ambient CO2 concentration, concomitant infection by both pathogens significantly reduced C assimilation rate (A) and light use efficiency (μmoles CO2 fixed per μmol of light used), and increased the intercellular CO2 (C i ) of these young leaves at 42 DAI, but not at 16 DAI. Infection by either pathogen alone had little or no effect on the leaf gas exchange parameters. Analysis of the curve relating A and C i showed that either treatment alone did not change the initial slope of the curve at 16 DAI. A significant reduction in both the initial slope of A vs. C i curves and A at C i = 500 μmol mol−1 in the jointly infected plants were noticeable at 42 DAI indicating that nonstomatal effects could explain the reduction in C assimilation rate at this late stage of disease infection. Leaf patchiness might also be a contributing factor to this phenomena in the leaves of the jointly infected plants.

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