Host infection and oospore formation by Peronospora parasitica in agricultural and horticultural Brassica species

A Comparison of Peronospora parasitica (Downy Mildew) Isolates from Arabidopsis thaliana and Brassica oleracea Using Amplified Fragment Length Polymorphism and Internal Transcribed Spacer 1 Sequence Analyses

“…Therefore, it is important to understand the relationship between the P. parasitica isolates that infect the model and the crop plant species. Downy mildew isolates collected from different host genera within the Brassicaceae vary in both their host range and the morphology of structures such as sporangia; however, neither character is suitable for dividing the downy mildews of this family into separate species (Dickinson and Greenhalgh, 1977;Kluczewski and Lucas, 1983;Sherriff and Lucas, 1990;Yerkes and Shaw, 1959). Therefore, downy mildews of any brassicaceous host are currently classified as the same species, P. parasitica (Waterhouse, 1973).…”

The identification of a gene for race‐specific resistance to Peronospora parasitica (downy mildew) in Brassica napus var. oleifera (oilseed rape)

“…Nevertheless, isolates often have the capacity to colonize and cause symptoms on some genotypes of heterologous crucifer species, i.e. different species to that from which the isolate was obtained (Dickinson & Greenhalgh, 1977;Kluczewski & Lucas, 1983;Sherriff& Lucas, 1987).…”

“…In Brassica oleracea L., genotypes exhibiting race-specific resistance to pathotypes adapted to this species have been reported (Nattie/a/., 1967). The spring-sown oilseed rape cultivar Cresor has proved resistant to isolates of P. parasitica collected from Brassica napus L. in the UK (Kluczewski & Lucas, 1983;Sherriff, 1986). Resistance in seedlings at the cotyledon stage was associated with necrotic flecks without sporulation or with sparse sporulation on a minority of seedlings.…”

Internal transcribed spacer 2 amplicon as a molecular marker for identification of Peronospora parasitica (crucifer downy mildew)

“…As the identification of P. parasitica is based on morphological characteristics of conidia and conidiophores (Dickinson and Greenhalgh 1977), downy mildew diagnosis on infected seedlings is delayed until sporulation occurs. The ineffectiveness of conventional identification methods is also a major concern in incompatible interactions with resistant hosts, where no pathogen reproduction occurs but tissue damage is observed , and in the detection of infected cabbage seeds, embedding intact or germinating oospores, mycelium and conidia (Kluczewski and Lucas 1983;Badul and Achar 1998). Conventional methods also cannot detect infected young brassica leaves packed in sealed plastic bags, which may develop sporulating lesions before reaching the consumer.…”