EXPRESSION OF RESISTANCE IN BRASSICARAPA INFECTED WITH PLASMODIOPHORA BRASSICAE

Abstract

Development of the secondary phase of Plasmodiophora brassicae was studied in susceptible and resistant lines of B. rapa by light and transmission electron microscopy. In infected plants grown at approximately 20⁰C in 10 hours light at 450 umole flux density, plasmodia developed and migrated through the susceptible and resistant outer cortical tissue for about 15 - 18days after inoculation. Subsequently, plasmodia developed rapidly, divided and migrated deeper into the root. In resistant lines the plasmodia failed to grow and divide after this stage; they could not be found in subsequent samplings. X-ray micro-analysis showed that Ca++ level increased considerably at the infection sites in resistant tissue, becoming concentrated in plasmodia and adjacent cell walls. These levels were consisderably in excess of the toxicity threshold and were assocaited with degenerations of the plasmodia. There were no major changes in other elements measured.