Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/15/2003
Publication Date: 3/1/2004
Citation: Paulitz, T.C., Dugan, F.M., Chen, W., Grunwald, N.J. 2004. First report of pythium irregulare on lentils in the united states. Plant Disease. 88 (3). p. 310-310. 2004 Interpretive Summary: In summer, 2000, lentils in eastern Washington and northern Idaho were affected by an unknown disease, which included stunting and yellowing of the plants. We isolated Pythium irregulare from diseased plants, and tested isolates in the greenhouse on cultivars Brewer and Mason. This pathogen caused root rot and stunting of plants in the greenhouse. This is the first report of P. irregulare attacking lentils in the field in the United States. This pathogen also attacks wheat, a rotation crop.
Technical Abstract: In late June-early July, 2002, stunted, chlorotic, and partially defoliated lentils (Lens culinaris Medik.) were observed throughout two fields near Garfield, WA and one field near Genesee, ID. Cultivar 'Mason' was more affected than cv. 'Brewer'. These symptoms were widespread in the lentil growing areas of eastern Washington in 2002. Roots were dry and brittle, with black discoloration in some cases. Isolates of Fusarium oxysporum and F. solani were obtained from washed roots plated on water agar, but they were non-pathogenic in greenhouse testing in pasteurized soil and peat-based growing mixes. In March, 2003, volunteer lentils growing in the same fields showed symptoms of root rot and Pythium oospores were observed in the roots. Pythium spp. were isolated using a selective medium. Oospores were aplerotic, intercalary, mostly smooth, and often formed in chains. Isolates resembled P. paroecandrum Drechs. and P. irregulare Buisman, based on morphological characters (1), but DNA sequences of the ITS region were closer to P. irregulare, based on a comparison with a worldwide database of Pythium sequences (C. A. Lévesque, pers. comm.). Isolates were deposited with USDA-ARS Western Regional Introduction Station, Pullman, WA. Four hyphal-tip isolates were tested in the greenhouse, using inoculum grown in autoclaved sandy loam amended with 1% ground rolled oats. Inoculum was added at 500 cfu/g. Experiments were performed twice, first in pasteurized soil and then in natural field soil. Each isolate was tested on cvs. Brewer and Mason, with five replicates per treatment. Plants were grown in 4 cm X 20.5 cm plastic tubes, for 1 month at 16 to 22 C, supplemented with 14 h light per day. P. irregulare was re-isolated from infected roots in both experiments. Damping-off, stunting, chlorosis and root rot were observed in the Pythium-inoculated treatments, corresponding to symptoms observed in the field in 2002. In pasteurized soil, only one isolate reduced the dry weight of Brewer, but 3 out of 4 isolates reduced the dry weight of Mason. All isolates reduced the root dry weight of Mason in natural soil, but only two isolates reduced the root dry weight of Brewer. Pythium spp., but not P. irregulare, have been reported previously from lentils (2). Pythium irregulare also causes root rot on winter wheat, which is rotated with lentils, and this pathogen likely causes yield reduction in both crops.