Response of resting spores of clubroot (Plasmodiophora brassicae WOR.) to temperature, some herbicides and chemicals under in-vitro-conditions: Reaktion von Dauersporen der Kohlhernie (Plasmodiophora brassicae Wor.) gegenüber Temperatur sowie einige

摘要

In several in-vitro-studies, in water suspended resting spores of the clubroot causing agent, Plasmodiophora brassicae, were exposed to temperature levels graduated between 20 and 100 °C as well as, applied in various concentrations, to approved herbicides Glyphosate 36% (Vorox G), Pyridate 45% (Lentagran EC), Metamitron 90% (Goltix WG), Prosulfocarb 80% (Boxer), and more/less aggressive chemicals (formaldehyde, lactic acid, hydrochloric acid, sulphuric acid). As parameter of resting spore viability, the proportion of inactive (dead) spores (mortality rate %) in the suspension, manifested by a fluorescence staining technique published by TAKAHASHI and YAMAGUCHI (1988), was used. All watery suspensions prepared from clubs comprised proportions of apriori inactive spores (initial mortality rate) ranging between 35 and 67%. With increasing time of exposition to the investigated several temperature levels (5 until 20 minutes) mortality rates increased. At 80 and 100 °C, 99% respectively 100% of thespores were dead. Significant deviation in mortality rates of suspensions containing differently pre-treated spores (storing at -18 and 5 °C, isolated from fresh clubs) became compensated by a temperature level at 70 °C. Herbicides were given in threeconcentrations following application rates recommended by the producer and as usual in agricultural practice. There were no reliable differences of impacts between the various concentrations employed, however, mortality of spores progressed with increasing exposition time from the first to the fourth day, i.e. about 18% (Goltix), 32% (Vorox), 34% (Lentagran) und 46% (Boxer) in relation to the control (spores suspended in water). There was the tendency that, when exposition time increased, differences tothe control became smaller (F = 12.93** , f_1 15 f_2 32 in the test on non-homogeneity), indicating different sensibility of resting spore population to herbicides. Chemicals were employed in solutions of a 1 : 10, 1 : 5 and 1 : 1 ratio with the wateryspore suspension under temperature regimes at 3 to 4 and 20 °C and in an exposition time over five days. Temperature as well as various concentration schedules did not effect spore viability in a reliable manner, but there was a significant positive connec-tion (correlation coefficients ranging from r = 0.56* to 0.98**) between the time of exposition and the level of mortality rates. By averaging all data of each treatment of concentration the increasing impulse compared with the control ranged formaldehyde (29%) < lactic acid (35%) < hydrochloric acid (68%) < sulphuric acid (69%). Sulphuric acid destroyed resting spores completely when mixed 1 : 1 with the spore suspension. Sensibility of resting spores to environmental impacts, its infectious powerand practical relevance is the main objective of the discussion.