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Soybean is an important crop in South Africa. Damping-off and root rot was observed in a lower lying patch (~ 1.5–2 m diam) of 5-week-old plants (cv DM.8i) in a commercial field near Atlanta, North West Province, (25°13’37.5” S; 27°32’31.3” E) in January 2020. Isolations from diseased roots yielded isolates resembling Pythium deliense (inflated filamentous sporangia, large intercalary antheridia, oogonial stalks curving towards antheridia; van der Plaats-Niterink 1981). Barcoding regions for oomycetes (internal transcribed spacers, cytochrome C oxidase subunit 1; Robideau et al. 2011), were sequenced for ten isolates (GenBank accessions: OM920863–OM920874, OM939729-OM939738). BLAST indicated high similarity (> 99.56% identity, ≥ 677 identical bases) to P. deliense CBS 314.33 (ex-type strain; ITS: AY598674; cox1: HQ708568). Maximum likelihood analyses of an ITS-cox1 dataset confirmed their identity as P. deliense. The pathogenicity of five isolates were evaluated under glasshouse conditions over 21 days. A pasteurized potting mix was inoculated with millet inoculum (0.5% w/w, Strauss and Labuschagne 1995) and planted to cultivar SSS 5052 (20 seeds/pot). Pots were watered daily. The trial was repeated once and each treatment replicated thrice. All isolates caused damping-off (10–30% plants surviving). Surviving seedlings exhibited root rot and lesions on hypocotyls and cotyledons. Control plants were asymptomatic. Pythium was reisolated and confirmed as P. deliense. Pythium deliense is known to cause soybean damping-off and root rot in Brazil, China, and India, but not previously in South Africa.
References
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Van der Plaats-Niterink AJ (1981) Monograph of the genus Pythium. Stud Mycol 21:1–242
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Lamprecht, S.C., Phasoana, T.J., Van Wyk, W. et al. First report of Pythium deliense causing damping-off and root rot of soybean in South Africa. J Plant Pathol 106, 771 (2024). https://doi.org/10.1007/s42161-024-01592-5
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DOI: https://doi.org/10.1007/s42161-024-01592-5