Comparing cotyledon, leaf and root resistance to downy mildew in radish (Raphanus sativus L.)

Abstract

AbstractRadish downy mildew (DM) caused by the oomycete Hyaloperonospora brassicae f. sp. raphani is a serious problem in radish crop, an edible root vegetable of the Brassicaceae family. The objective of this research was to assess radish germplasm for DM resistance and to evaluate the response of different radish organs to the disease under controlled conditions. Forty-four radish accessions were inoculated at cotyledons and true-leaves with H. brassicae isolate R10, collected in cotyledons of field plants. The roots were tested with isolates R10 and R6, this last one collected in roots of field radish. DM symptoms varied with the radish genotype and plant organ analysed. Twenty-seven resistant and partially resistant accessions were identified in all plant stages and are promising sources of resistance to DM, namely 16 commercial varieties, 10 breeding lines, and one landrace. A significant correlation was observed between cotyledon and leaf (1st and 2nd leaves) DM resistance, but low and no correlation was found between the resistance of true-leaves or cotyledons and roots, respectively. Cotyledon and leaf evaluation cannot be used to predict root resistance response in radish. However, cotyledon resistance has its own value because non-infected cotyledons will act as a barrier to slow disease progression to true-leaves and roots. Interesting sources of DM resistance were identified that can be used in radish breeding programs.