Chemical control of Phytophthora sojae : sensitivity of isolates and effects on soybean seed germination and seed rot

Abstract

Phytophthora sojae is an oomycete responsible for causing seedling damping-off and root and stem rot in soybean. Seed treatment with chemical products is one of the management strategies that can be used to control the disease. Thus, the objective of this study was to evaluate the in vitro sensitivity of P. sojae isolates to commercial fungicide products and their effects on soybean seed germination and seed rot. An in vitro sensitivity test on mycelial growth was conducted using five P. sojae isolates (Race 1, Race 3, Race 4, Race 25, and Bra_1) and seven concentrations (0, 0.1, 1, 5, 10, 50, and 100mgL−1 ) of six commercial products containing active ingredients effective against oomycetes [Apron RFC (mefenoxam + fludioxonil), Maxim Advanced (mefenoxam + thiabendazole + fludioxonil), Certeza N (fluazinam + thiophanate-methyl), LumiTreo (oxathiapiprolin + picoxystrobin + ipconazole), Standak Top (pyraclostrobin + thiophanate-methyl + fipronil), and Vitavax-Thiram (thiram + carboxin)]. In the second stage of the study, ‘NEO580 IPRO’ soybean seeds were treated with the label-recommended doses of the commercial products, and germination and seed rot were evaluated in vitro on agar medium colonized with the oomycete. All P. sojae isolates were highly sensitive to products containing oxathiapiprolin and mefenoxam, which reduced mycelial growth and seed rot severity and promoted higher soybean seed germination. LumiTreo, Apron RFC, and Maxim Advanced were the most effective treatments for controlling P. sojae under in vitro conditions, reducing seed rot severity by 76.2%, 55.9%, and 52.9%, respectively, compared with the untreated control, while maintaining seed germination above 97.5%. These results highlight their potential for use in the chemical management of this pathogen.