Gj. Van Os et Jh. Van Ginkel, Suppression of Pythium root rot in bulbous Iris in relation to biomass andactivity of the soil microflora, SOIL BIOL B, 33(11), 2001, pp. 1447-1454
Disease suppression against Pythium root rot can be influenced by managemen
t practices applied in ornamental bulb culture. Different levels of suppres
sion were established in sandy soil after several soil treatments. Percenta
ge of infection in Iris caused by Pythium macrosporum was lowest in untreat
ed soil and progressively increased in sterilized soil amended with 1% comp
ost, fumigated soil (methylisothiocyanate) and flooded soil (fumigation and
flooding corresponding to the same level of disease severity) and was high
est in sterilized soil. The relationship between the level of disease incid
ence, Pythium growth rate through soil, and various microbial parameters wa
s investigated. Soil microbial biomass and, after amendment of glucose as a
non-selective carbon source, dehydrogenase activity, glucose uptake and re
spiration were determined. By using C-14-labelled glucose, measurement of u
ptake and assimilation of amended carbon could be distuingished from soil o
rganic matter decomposition. All microbial parameters were negatively assoc
iated with Pythium growth rates, indicating that high microbial biomass and
activity induced suppression of Pythium growth through soil. However, with
neither of the quantitative microbial parameters could chances in disease
incidence be fully explained. It is hypothesized that competition for carbo
n may not be the main mechanism in disease suppression. (C) 2001 Elsevier S
cience Ltd. All rights reserved.