Resistances to downy mildew (Hyaloperonospora brassicae) in diverse Brassicaceae offer new disease management opportunities for oilseed and vegetable crucifer industries

Some 154 Brassicaceae genotypes (78 Brassica napus, 38 B. carinata, 25 B. juncea, three Raphanus sativus, two each of Rapistrum rugosum and B. incana and one each of Crambe abyssinica, B. fruticulosa, Hirschfeldia incana, B. insularis, B. oleracea and Sinapis arvensis), were inoculated with a mixture of seven isolates of Hyaloperonospora brassicae to identify effective host resistances. Many highly resistant genotypes were identified, particularly R. sativus Krasnodar Market B (%Disease index 6.6) and Pegletta (%DI 9.0); B. carinata Tamn Rex-sel Green (%DI 7.6), BRA926/18 (%DI 9.7) and PI360884 (%DI 9.7); and B. juncea, Ringot1 (%DI 9.7). A further 13 B. carinata, seven B. juncea and single R. sativus (Boss) and B. incana (UPM6563) genotypes were also highly resistant (%DI 11.1), as were B. oleracea CPI106844 (%DI 14.6) and Crambe abyssinica (%DI 17.4). Almost all B. carinata and B. juncea genotypes showed high resistance (%DI 7.6-22.2). In contrast, B. napus genotypes showed wide ranging responses, from high resistance in SN-8 (%DI 22.2%) to extreme susceptibility in Hyola 450TT and Thunder TT (%DI 83.7, 95.5, respectively). R. rugosum, B. fruticulosa, H. incana and B. insularis genotypes ranged from moderately to highly susceptible (%DI 55.2-78.8). This study highlights the ready availability of very high levels of pathotype-independent resistance across diverse Brassicaceae to H. brassicae, particularly R. sativus, B. carinata, B. juncea, B. oleracea and C. abyssinica. Resistances identified can be utilized as sources of resistance in oilseed and vegetable Brassicaceae breeding programs and/or directly deployed as new varieties where downy mildew is prevalent.