The Role of Primary and Secondary Infection in Host Response to Plasmodiophora brassicae

Abstract

The disease cycle of Plasmodiophora brassicae consists of a primary phase in root hairs followed by a secondary phase in the root cortex and adjacent tissues. However, the role of root hair infection in subsequent cortical infection and development of P. brassicae is not well understood. To examine the role of the primary and secondary stages separately, inoculation studies with resting spores (source of primary zoospores) and secondary zoospores of a virulent and avirulent pathotype were conducted on canola (Brassica napus). The size of secondary zoospores and number of nuclei were also examined. The zoospores were larger (≈9.6 to 14.4 μm) than in previous reports and all were uninucleate. Inoculation with secondary zoospores alone produced both primary and secondary infection, even with the avirulent pathotype. No symptoms developed from inoculation with avirulent primary zoospores but tiny, bead-shaped clubs developed from inoculation with avirulent secondary zoospores. Inoculation with virulent secondary zoospores alone resulted in lower disease severity than inoculation with virulent resting spores alone. The results indicate that recognition of infection by the host and initiation of a response (induction or suppression of resistance) occurs during primary infection, although recognition can also occur during cortical infection and development.

Transcriptome Analysis of Arabidopsis thaliana in Response to Plasmodiophora brassicae during Early Infection

“…These results suggest that the early infection stage (24 and 48 hpi) is a key phase for the recognition and interaction between A. thaliana and P. brassicae . This is consistent with the hypothesis of McDonald et al, who stated that recognition between P. brassicae and its host, as well as successful cortex infection, may occur during the root-hair infection phase (McDonald et al, 2014). …”

“…In previous studies, the cortical infection stage was considered to be the most important. In recent years, some researchers have suggested that root-hair infection also plays an important role, although there is little evidence (Macfarlane, 1958; Siemens et al, 2002; Malinowski et al, 2012; McDonald et al, 2014). High-throughput sequencing technologies have been used to study the pathogenic process and pathogenesis of infection by P. brassicae .…”

Reducing the build‐up of Plasmodiophora brassicae inoculum by early management of oilseed rape volunteers

“…The findings confirm the results obtained by McDonald et al . (), which demonstrated under controlled conditions that primary root hair infection occurred one day after inoculation and secondary zoospores were released approximately 3–5 days after primary infection. Hence, secondary infection can occur as early as 4 dpi.…”

Integrated omics study of lipid droplets from Plasmodiophora brassicae

“…Proliferation of secondary plasmodia is associated with infected and neighboring uninfected cells undergo extreme cell division and expansion, leading to the formation of characteristic galls. After a number of nuclear divisions, the secondary plasmodia develop into multinuclear plasmodia and finally into resting spores, which are released into the surrounding soil when the gall disintegrates10.…”