Most isolates belonging to the Bacillus amyloliquefaciens subsp. plantarum clade retain the potential to produce a vast array of structurally diverse antimicrobial compounds that largely contribute to their efficacy as biocontrol agents against numerous plant fungal pathogens. In that context, the role of cyclic lipopeptides (CLPs) has been well-documented but still little is known about the impact of interactions with other soil-inhabiting microbes on the expression of these molecules. In this work, we wanted to investigate the antagonistic activity developed by this bacterium against Rhizomucor variabilis, a pathogen isolated from diseased maize cobs in Democratic Republic of Congo. Our data show that fengycins are the major compounds involved in the inhibitory activity but also that production of this type of CLP is significantly upregulated when co-cultured with the fungus compared to pure cultures. B. amyloliquefaciens is thus able to perceive fungal molecules that are emitted and, as a response, up-regulates the biosynthesis of some specific components of its antimicrobial arsenal.
In the province of South Kivu (Democratic Republic of Congo), warm and humid climatic conditions favor the development and spreading of phytopathogens. The resulting diseases cause important losses in production both in crop and after harvest. In this study, we wanted to evaluate the potential of Bacillus amyloliquefaciens as biocontrol agent to fight some newly isolated endemic fungal pathogens infesting maize. The strain S499 has been selected based on its high in vitro antagonistic activity correlating with a huge potential to secrete fungitoxic lipopeptides upon feeding on maize root exudates. Biocontrol activity of S499 was further tested on infected plantlets in growth chamber and on plants grown under field conditions over an entire cropping period. We observed a strong protective effect of this strain evaluated at two different locations with specific agro-ecological conditions. Interestingly, disease protection was associated with higher yields and our data strongly suggest that, in addition to directly inhibit pathogens, the strain may also act as biofertilizer through the solubilization of phosphorus and/or by producing plant growth hormones in the rhizosphere. This work supports the hope of exploiting such technologically advantageous bacilli for the sake of sustainable local production of this important crop in central Africa.
Common bean (Phaseolus vulgaris) is the main leguminous crop grown in South-Kivu province. However, there is a scarcity of information concerning the soil mycorrhizal potential, natural mycorrhization and the spore density of arbuscular mycorrhizal (AM) fungi associated with P. vulgaris in South-Kivu province. In this study, rhizospheric soil and roots samples have been collected in Kabare and Walungu territories in famer’s field (three localities in each territory) to determine the bean natural mycorrhization rate, AM spore density and the soil mycorrhizal potential in relation with soil chemical properties. We founded that bean root colonization was high in Katana, Kavumu and Miti, and low in Lurhala, Walungu centre and Nduba. Katana and Kavumu showed a high number of spores (242.9 ± 37.8 and 183 ± 13.1 spores.100g− 1 soil, respectively) compared to other sites. Soil mycorrhizal potential was higher in Katana, Kavumu and Miti sites, located in Kabare territory (10.8 ± 0.7, 9 ± 1.3 and 8.8 ± 0.9 AM propagules g-1 soil). AM potential was positively and significantly correlated with bean mycorrhizal colonization (p < 0.0001). Increasing soil P content significantly decreased mycorrhization frequency and intensity (r=-0.69, p < 0.0001 and r=-0.54, p = 0.002, respectively) and the soil mycorrhizal potential (r= -0.87, p < 0.0001) regardless of the study site. While soil pH positively affected the mycorrhizal colonization (r = 0.73, p < 0.0001 and r = 0.54, p = 0.002, respectively) and the soil mycorrhizal potential (r = 0.78, p < 0.0001). This study revealed a strong variation in bean mycorrhizal status and soil mycorrhizal potential across sites. Site-specific AM fungi morphotype identification and inoculum production should be considered to improve bean productivity.
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