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Synergism of Pratylenchus penetrans and Verticillium dahliae Manifested by Reduced Gas Exchange in Potato

April 1997 , Volume 87 , Number  4
Pages  435 - 439

Ibrahim A. M. Saeed , Ann E. MacGuidwin , and Douglas I. Rouse

Department of Plant Pathology, University of Wisconsin, 1630 Linden Drive, Madison 53706

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Accepted for publication 14 January 1997.

The effects of solitary and concurrent infection by Pratylenchus pene-trans and Verticillium dahliae on gas exchange of Russet Burbank potato (Solanum tuberosum) were studied in growth chamber experiments. Treatments were P. penetrans at low, medium, and high density; V. dahliae alone at one initial density; the combination of the nematode at these three densities and V. dahliae; and a noninfested control. Gas exchange parameters of leaf cohorts of different ages in the different treatments were repeatedly measured with a Li-Cor LI-6200 portable photosynthesis system. At 45 days after planting, joint infection significantly reduced net photosynthesis, stomatal conductance, and transpiration of 1- to 25-day-old leaf cohorts. Intercellular CO2 levels were significantly increased by co-infection, especially in older leaves. The synergistic effect of co-infection on gas exchange parameters was greater in the oldest cohort than in the youngest cohort. No consistent effects on leaf gas exchange parameters were observed in plants infected by the nematode or the fungus alone. The relationship between the assimilation rate and stomatal conductance remained linear regardless of solitary or concomitant infection, indicating that stomatal factors are primarily responsible for regulating photosynthesis. The significant reduction of gas exchange in leaves of co-infected plants without reduction in intercellular CO2 concentrations suggests that nonstomatal factors also play a role when both organisms are present.

Additional keywords: light use efficiency, potato early dying, root-lesion nematode, water use efficiency.

© 1997 The American Phytopathological Society