Abstract
Shifts in the soil microbiome during continuous monoculture cropping coincide with increased suppressiveness against soil-borne diseases, as in the take-all decline of wheat. Here we report a similar phenomenon for bacterial blotch of mushrooms, caused by Pseudomonas ‘gingeri’, where ginger blotch incidence decreases during consecutive cycles of mushroom cultivation. We explored the infection dynamics of blotch during consecutive cultivation cycles for different casing soil mixtures. We also observed the population dynamics of the pathogen in these casing soils. In addition, the composition of the casing soil microbiome was compared between blotch suppressive and conducive soils. Finally, we studied the transferability of blotch suppressiveness. A consistent decline of bacterial blotch was observed for two consecutive cultivation cycles of mushroom cropping, across ten casing soil mixtures composed of different peat sources and supplements. Blotch suppression occurred without reduction of pathogen populations in the casing soils. Aqueous extracts made from suppressive soils were able to reduce blotch incidence in conducive casing soils, indicating that blotch suppression is transferrable and microbially mediated. Changes in the microbial community composition of the casing soils reflected pathogen invasion, pathogen establishment and disease suppression, in addition to the expected temporal changes across the cultivation cycles. Specific bacterial genera were associated with soil suppressiveness to bacterial blotch, such as, Pseudomonas sp., Dyadobacter sp., Pedobacter sp., and Flavobacterium sp. We suggest that the suppression of bacterial blotch is induced due to high pathogen populations in the first cultivation cycle, and mediated by inhibition of virulence factors such as those controlled by quorum sensing in the later cultivation cycles.
Highlights
Management of soil-borne diseases via suppressive soils remains a promising yet significant challenge in intensive cropping systems (Gomez Exposito et al, 2017; Stirling et al, 2016)
Bacterial blotch suppressiveness in mushroom casing soils was studied in an experimental mushroom cultivation facility (Unifarm, Wageningen University & Research) under conditions that resemble that of conventional mushroom farms
This study reported induced soil suppressiveness to bacterial blotch between consecutive cultivation cycles of mushroom cropping systems
Summary
Management of soil-borne diseases via suppressive soils remains a promising yet significant challenge in intensive cropping systems (Gomez Exposito et al, 2017; Stirling et al, 2016). Studies from diverse soils have attributed disease suppression to the composition and the activity of the soil microbial community (Benítez and Gardener, 2009; Penton et al, 2014; Poudel et al, 2016). Changes in the soil microbiome during consecutive growth of crop monocultures that are susceptible to the disease, or inoculation of high pathogen populations into the soil are known to induce soil suppression of fungal pathogens (Hornby, 1983; Pervaiz et al, 2020; Weller et al, 2002). With current developments in -omic technologies, it is increasingly possible to characterize the microbial composition, networks and ac tivity of disease suppressive soils (De Corato, 2020a; Klein et al, 2013; Mendes et al, 2011). An ideal sector for improving our understanding of disease suppressive soils is controlled horticulture, which are closed cropping systems, independent of agricultural land and where the growth conditions are constantly regulated (Kulak et al, 2013; Marcelis et al, 2007)
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