Soil bacterial community was changed after Brassicaceous seed meal application for suppression of Fusarium wilt on pepper

Application of Brassicaceous seed meal (BSM) is a promising biologically based disease control practice. Directly and indirectly, BSM incorporation could affect the non-target bacterial community, including the beneficial populations. Understanding the bacterial response to BSMs at the community level is of great importance for directing the plant disease management through manipulation of resident bacterial communities. Fusarium wilt is a devastating disease on pepper. However, little is known about the response of soil bacterial communities, especially the rhizosphere bacterial community, to BSM application under the condition that the pepper plant was infected by Fusarium wilt pathogen. In this study, a 25-day of microcosm incubation with supplementation of three BSMs, i.e., Camelina sativa 'Crantz' (CAME), Brassica juncea 'Paci?c Gold' (PG), and a mixture of PG and Sinapis alba cv. 'IdaGold' (IG) (PG+IG, 1:1 ratio), was performed based on a natural Fusarium wilt pathogen-infested soil. Then, a further 35-day of pot experiment was established with pepper plant growing in the BSMs treated soils. The changes of bacterial community from the soil after 25 days of incubation and from the rhizosphere after 35 days of further pepper growth was investigated by 454 pyrosequencing technique. The results show that PG and PG+IG application reduced disease index by 100% and 72.8%, respectively after 35 days of pepper growth while CAME exhibited no evident suppressive effect. All BSMs treatments altered the bacterial community structure and decreased the bacterial richness and diversity after 25 days of incubation while this effect was weakened after a further 35 days of pepper growth. At the phylum/class and the genus level, the changes of specific bacterial populations resulting from PG and PG+IG treatments, especially the significant increase in Actinobacteria-affiliated Streptomyces and an unclassified genus as well as the significant decrease in Chloroflexi were suspected to be one of the microbial mechanisms that is involved in PG-containing BSMs-induced disease suppression. This study is helpful for our understanding the mechanisms that lead to the contrasting plant disease severity under addition of different BSMs.