J o u r n a l o f Nematology 30(1):100-107. 1998. © T h e Society o f Nematologists 1998.
Effect of Initial Nematode Population Density on the Interaction of Pratylenchus penetrans and Verticillium dahliae on 'Russet Burbank' Potato 1 I. A. M. SAEED, A. E. MACGUIDWIN, AND D. I. ROUSE 2 Abstract: Four similar growth c h a m b e r e x p e r i m e n t s were c o n d u c t e d to test the hypothesis that the initial population density (Pi) o f Pratylenchus penetrans influences the severity of interactive effects o f P. penetrans a n d Verticillium dahliae o n s h o o t growth, photosynthesis, a n d t u b e r yield of Russet B u r b a n k potato. In each e x p e r i m e n t , three population densities o f P. penetrans with a n d without c o n c o m i t a n t inoculation with V. dahliae were c o m p a r e d with nematode-free controls. T h e three specific Pi of JR penetrans tested varied f r o m e x p e r i m e n t to e x p e r i m e n t b u t fell in the ranges 0.8-2.5, 1.8-3.9, 2.1-8.8, a n d 7.5-32.4 n e m a t o d e s / c m s soil. I n o c u l u m o f V. dahliaewas m i x e d into soil, a n d the assayed density was 5.4 p r o p a g u l e s / g r a m dry soil. Plants were grown 60 to 80 days in a controlled e n v i r o n m e n t . Plant growth parameters in two e x p e r i m e n t s indicated significant interactions between P. penetrans a n d V. dahliae. In the absence o f V. dahliae, P. penetrans did n o t reduce p l a n t growth a n d tuber yield below that of the nematode-free control or did so only at the h i g h e s t one or two population densities tested. In the presence of K dahliae, the lowest population density significantly r e d u c e d s h o o t weight a n d photosynthesis in three a n d four experiments, respectively. H i g h e r densities h a d n o additional effect o n s h o o t weight a n d caused additional reductions in photosynthesis in only o n e experiment. Population densities o f 0.8 a n d 7.5 n e m a t o d e s / c m 3 soil r e d u c e d t u b e r yield by 51% a n d 45%, whereas h i g h e r densities h a d n o effect or a 15% additional effect, respectively. T h e s e data indicate that interactive effects between P. pcnetrans a n d K dahliae o n Russet B u r b a n k potato are manifested at P. penetrans population densities less t h a n 1 n e m a t o d e / c m 3 soil a n d that t h e n e m a t o d e population density m u s t be substantially h i g h e r before additional effects are apparent. Key wards: c o n c o m i t a n t populations, disease complex, fungus, interaction, lesion n e m a t o d e , n e m a tode, potato, potato early dying, Pratylenchus penetrans, root-lesion n e m a t o d e , Solanum tuberosum, VerticilIium dahliae, Verticillium wih.
The root-lesion nematode, Pratylenchus penetrans, is endemic to potato (Solanum tuberosum) production areas in the northeastern United States and Canada (Townshend et al., 1978). Studies using controlled inoculum densities of P. penetrans demonstrated reduced tuber yields for nematode-infected potato cultivars Sebago (Olthof and Potter, 1973), Yukon Gold, M o n o n a , N o r c h i p (Olthof, 1986), S u p e r i o r ( B e r nar d and Laughlin, 1976; Olthof, 1986), Katahdin (Bernard and Laughlin, 1976), Kennebec ( B e r n a r d an d L aughl i n, 1976; Olthof, 1986), Voran (Oostenbrink, 1958), and Russet B u r b a n k (Olthof, 1983, 1986). Enhanced yields in infested fields treated with
Received for publication 11 Februal7 1997. 1 Supported by a grant from the USDA NRI (#92-3702-7609) and funds from the Wisconsin Potato and Vegetable Growers Association. 2 Department of Plant Pathology, University of WisconsinMadison, Madison, WI 53706. E-mail:
[email protected] The authors thank Thomas Sharkey for advice, Murray Clayton for statistical consulting, and Steve Vicen for assistance in figm'e preparation.
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nematicides are also evidence of the pathogenicity of P. penetrans to Superior potato (Kimpinski and McRae, 1988; Vitosh et al., 1980). A synergistic interaction of P. penetrans and Verticillium dahliae has been demonstrated to reduce yields and tuber quality of both Superior (Botseas and Rowe, 1994; Martin et al., 1982; Rowe et al., 1985) and Russet Burbank (MacGuidwin and Rouse, 1990) potato. In field (MacGuidwin and Rouse, 1990; Wheeler et al., 1994) and microplot (Kotcon et al., 1985; MacGuidwin and Rouse, 1990; Rowe et al., 1985) studies, initial inoculum densities of the nematode and fungus too low to cause a deleterious effect alone caused foliar symptoms and reduced yield when present together. Yield of Superior potato grown in soil infested by both V. dahliae and P. penetrans was more responsive to changes in the initial inoculum density of the fungus than to that of the nematode (Rowe et al., 1985). Using data from this and s u b s e q u e n t studies, Francl et al. (1987) developed a predictive
Pratflenchus penetrans, VerticiUium dahliae o n potato: Saeed et al. 101 model that linearly related yield loss of Su- the nature o f this nematode-fungus interacperior potato to the logarithm of the prod- tion. uct o f V. dahliae and P. penetrans population densities at planting. Francl et al. (1987) MATERIALS AND METHODS n o t e d that his model assumed equivalence Four experiments were c o n d u c t e d in a of the fungus and n e m a t o d e in the interaccontrolled plant growth facility from Janution. Wheeler et al. (1992) followed with a ary 1993 to April 1994. T r e a t m e n t s were model that excluded P. penetrans density as a three inoculum levels o f Pratylenchus penetseparate algebraic term in the model but rans, alone and in combination with one which included a m i n i m u m relative yield level of Verticillium dahliae, V. dahliae alone, term, the value of which differed d e p e n d i n g and an uninfested control. T h e treatment o n the presence or absence o f P. penetrans. structure a n d e x p e r i m e n t a l design (ranT h e i r model was based on 5 years of yield domized complete block with four replicadata from microplots infested with 0 to 5 P. dons) were c o m m o n to all experiments, but penetrans/cm ~ soil. Bernard and Laughlin the n e m a t o d e inoculum level varied a m o n g (1976) also observed a limit in the yield reexperiments (see Table 1 for initial populaduction o f S u p e r i o r potato infected with tion densities). only P. penetrans. In their study, initial inocuRusset B u r b a n k potato was p r o p a g a t e d lum densities (Pi) o f 38 a n d 210 nemafrom dssue culture stock and planted either todes/100 cm 3 soil gave similar reductions as s p r o u t e d m i c r o t u b e r s in p a s t e u r i z e d in yield o f Superior potato. Plainfield loamy sand soil (92% sand, 5% T h e r e are insufficient data on the relasilt, 3% clay;
