The Host Range of Downy Mildew, Peronospora parasitica, from Brassica oleracea, Cabbage and Broccoli Crops.

Abstract

We collected three cabbage plants infected with Peronospora parasitica in Kagawa, two broccoli plants in Mie and one broccoli plant in Tottori. Five single spore isolates from each sample were prepared, and the host range of thirty single spore isolates in total was examined. Test plants used for the host range tests were Brassica oleracea (eighteen cultivars of cauliflower, cabbage and broccoli), B. campestris (eight cultivars of Pak-choi, mizuna, rape, Chinese cabbage and turnip), B. juncea (one cultivar of leaf mustard), B. napus (one cultivar of rutabaga) and Raphanus sativus (two cultivars of Japanese radish). In all the test plants, cotyledons with hypocotyl were used for the inoculation tests. All the B. oleracea plants except two cultivars of cabbage were highly susceptible to all the tested isolates, and it is considered that this is a host species of the fungus. B. napus was moderately susceptible, and suggested to be a possible host species. B. campestris, B. juncea and R. sativus were resistant, and considered to be non-host species. Therefore, all the isolates were considered to belong to the same strain of the fungus and the strain to be specific to B. oleracea and possibly to B. napus. Among B. oleracea plants, two cultivars of cabbage cv. Golden Best and cv. YR-Sawamidori were resistant. Difference in pathogenicity was not found among the tested single spore isolates.