Relation of Ca^<2+> Efflux to Germination of Resting Spores of Clubroot Fungus

The interrelation between the release of Ca^<2+> from resting spores and the spore germination of the clubroot fungus (Plasmodiophora brassicae WORONIN) was investigated by the quantitative analysis of Ca^<2+> in spore suspensions and also by inoculation of Chinese cabbage plants in culture solution with spores treated with chelating reagents. Considerably high concentration of Ca^<2+> was detected in the spore suspension prepared with deionized water, and Ca^<2+> concentration in the suspension became higher as the spore density increased in the suspension. This result confirmed that resting spores release Ca^<2+> in the suspension. Treatment of resting spores with EDTA or EGTA increased the amount of Ca^<2+> released from the sproes. Numbers of root-hair infection sites (zoosporangial masses) per plant, however, showed the maximum when resting spores were treated with 10 μMEDTA or 1μMEGTA, and logarithmically decreased when the spores were treated with higher concentration of these reagents. It became clear that EDTA and EGTA had their own concentrations promoting or inhibiting germination of resting spores. These results suggest that the release of an adequate amount of Ca^<2+> from resting spores promotes germination of resting spores.

Plasmodiophora brassicae

spore germination

calcium ion

chelating reagent