A. Wennstrom et al., THE DYNAMICS OF THE PLANT LACTUCA-SIBIRICA AND THE FREQUENCY OF ITS RUST PUCCINIA-MINUSSENSIS IN RIVER VALLEYS IN NORTHERN SWEDEN, Oikos, 72(2), 1995, pp. 288-292
The population dynamics of the rust Puccinia minussensis and its host
plant Lactuca sibirica were studied in four localities. Three of the l
ocalities were subjected to different degrees of erosion and/or deposi
tion (Kukkola, Aspliden and Hummelholm) during flooding, while one loc
ality (Langed) was situated above the flood level. At Kukkola and Humm
elholm both the densities of the host plant L. sibirica and the freque
ncy of the rust P. minussensis varied markedly within transects. At th
e other two localities, Langed which is not disturbed and Aspliden whi
ch is dry and subjected to erosion, densities and disease frequencies
remained constantly low between the years. There was a positive correl
ation between host densities and frequency of aecia-producing shoots a
t Hummelholm. However, it is suggested that this correlation is caused
by similar responses to variation in environmental conditions and not
by a response of the pathogen to host plant densities. Furthermore we
found that systemically diseased shoots (aecia) at all localities die
d before August, while uredial and telial stages did not cause death o
f shoots. It is suggested that (1) the host densities are primarily re
gulated by stochastic disturbances and (2) the direct and close fit in
the response of the fungus is due to resource limitation.