Electron microscopic studies on the root hairs and cortex of a susceptible and a resistant variety of Brassica campestris infected with Plasmodiophora brassicae

Abstract

The cortex of the roots of a susceptible and a resistant variety of Brassica campestris var. rapa infected with sterile resting spores of Plasmodiophora brassicae from senescent callus was studied at a stage prior to disease symptom development. Electron micrographs show the presence of amoeboid structures within the cortical cells of the susceptible variety 10 days after inoculation. Cell wall perforations, hypertrophied host cell nuclei, nucleoli and broken tonoplasts were frequently found in the susceptible variety. It has been concluded that amoeboid structures of the parasite penetrate the cell wall and disrupt the cortical cells.Electron micrographs of the resistant variety show the presence of zoosporangia with secondary zoospores in the root hairs nine days after inoculation. Two to four days later a large number of dead host cells can be observed in the outer cortical layer of the resistant variety, whereas no apparent changes are found in the inner cortex. The results suggest the occurrence of a hypersensitive host reaction which terminates further growth ofPlasmodiophora brassicae.

Root hair infection by Plasmodiophora brassicae in clubrootresistant and susceptible genotypes of Brassica oleracea, B. rapa and B. napus

“…Root hair infection has also been reported in some host species with complete resistance (Butcher et al, 1976;Dekhuijzen, 1979). In a resistant B. rapa genotype, the resistance was shown to be caused by a hypersensitive reaction in the root cortex (Dekhuijzen, 1979).…”

Concentrations of indole‐3‐acetic acid in plants of tolerant and susceptible varieties of Chinese cabbage infected with Plasmodiophora brassicae Woron.

“…Perhaps the high IAA contents during the first day of infection indicate that primary infection takes place also m the tolerant varieties, which resist secondary infection. Secondary infection (clubroot development) was found only in susceptible Brassicaceae, whereas primary infection was observed also in resistant Brassica species (Dekhuijzen, 1979Kroll, Lacy & Moore, 1983) and in plants not belonging to the Cruciferae (Karling, ). An interesting result was obtained when comparing the IAA content of 14-d infected and control plants of 'Granat' and 'Parkin' which were cultivated in soil and in liquid medium (Table 1).…”

Analysis of global host gene expression during the primary phase of the Arabidopsis thaliana–Plasmodiophora brassicae interaction

“…It is the secondary phase that produces the characteristic disease symptoms of root tissue hypertrophy and hyperplasia, or 'clubbing'. Broadly speaking, in resistant hosts, the primary phase of the lifecycle can still be observed, but not the secondary phase (Dekhuijzen 1979;Takahashi et al 2006;Donald et al 2008). In a compatible (susceptible) interaction with Arabidopsis thaliana (L.) Heynh., the pathogen can proceed through its entire lifecycle from 3 to 28 days, as studied by Siemens et al (2002).…”