Non-monotonic influence of biochar dose on bean seedling growth and susceptibility to Rhizoctonia solani: the “Shifted Rmax-Effect”
Biochar affects the progress of plant diseases caused by soilborne pathogens, frequently featuring U-shaped biochar dose/disease response curves. This study tested this phenomenon in common bean (Phaseolus vulgaris L.) with several biochars.
Four biochars prepared from two feedstocks (eucalyptus wood and greenhouse wastes) each at 350 and 600 °C were tested on bean seedling growth and infection caused by Rhizoctonia solani at concentrations of 0–3 % by weight. Biochar direct toxicity to R. solani was quantified in vitro.
In general, lower concentrations (≤1 %) of biochar suppressed damping-off, whereas higher concentrations (3 %) were ineffective at disease protection. Plant growth in the absence of the pathogen was generally improved at all doses by the four biochars. Maximum growth response (G-Rmax) generally occurred at higher biochar doses than maximum disease reduction (D-Rmax). Direct toxicity to the pathogen could not explain disease reduction.
Inverted U-shaped biochar dose/plant growth and biochar dose/disease reduction curves are emerging as common patterns in biochar/crop/pathogen systems. Frequently, the inflection between growth promotion and suppression occurs at different doses than the inflection between disease suppression and promotion. We term this the “Shifted Rmax-Effect”. As there is no simple rule-of-thumb for crop/soil/biochar/dose/pathogen combinations, the possible effects of biochar on plant pathogens should not be overlooked.
KeywordsBiotic stress Hormesis effect Plant disease Plant productivity Soil amendment Soilborne pathogen
Area under mortality progress curve
Colony forming units
Effective concentration for 50 % growth inhibition
Eucalyptus wood chips
Gas chromatography - mass spectrometry
Greenhouse pepper plant wastes
Highest Treatment Temperature
We thank Indira Paudel, Dalia Rav David, Prof. Dani Shtienberg, Dr. Yephet Ben-Yephet, Menahem Borenshtein, Ludmilla Tsechansky, and Ran Shulhani for their help in the experiments. We would also like to thank three anonymous reviewers for their valuable advice. The research was funded by The Chief Scientist of the Ministry of Agriculture and Rural Development, Israel. Project no: 1321653. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No: 546/14
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