Research of Plant Research International, part of Wageningen UR, shows that soil susceptible to Rhizoctonia solani can be made suppressive to this soil disease by inoculating the soil with R. solani one or several times. Fields on which cauliflower had been grown in the past were also found to be disease-suppressing.
Photo: Left: cauliflower soil; right: pear orchard soil
The suppressive soil contained a large amount of Lysobacter, a bacterium with a suppressing effect on R. solani. Although the mechanism behind the soil suppressiveness to R. solani is still unclear, the important role of this bacterium in the control of R. solani is reconfirmed.
The study involved investigation of the soil suppressiveness in two marine clay soils. One soil had a 40-year cauliflower history; the other soil originated from a pear orchard on which no cauliflower had been grown for 40 years. Both soils were either grown with cauliflower for five consecutive times or the soil was left uncropped for five years. They cauliflower-cropped soil was inoculated with R. solani once or for each crop. Soil suppressiveness was measured in a germination test and by measurement of the spreading of disease symptoms in young plants.
The results showed that all cauliflower-planted soil was suppressing R. solani. The suppressive properties, however, were considerably stronger in the soils inoculated with R. solani in the consecutive cauliflower cultivations. The suppressive soils contained a much higher percentage bacteria with the capability to suppress the soil pathogen R. solani. These bacteria were identified as Lysobacter (56%), Streptomyces (23%) and Pseudomonas (21%).
The role of Lysobacter in soil suppressiveness was confirmed in a Taqman PCR detection test. This showed that much more Lysobacter was present in the suppressive cauliflower soil than in the non-suppressive pear orchard soil.
Joeke Postma, researcher at Plant Research International and first author of the scientific publication in Soil Biology & Biochemistry about this research, states: ‘Although the mechanism behind the soil suppressiveness of Rhizoctonia solani is not yet clear it has again been shown that the antagonistic Lysobacter plays an important and promising key role in this process.’