Fusarium wilt on pepper in brassicaceous seed meal amended soil and associated bacterial community changes. Fusarium wilt on pepper in brassicaceous seed meal amended soil and associated bacterial community changes

Understanding the relationship between plant disease index after amendment of brassicaceous seed meal (BSM) differing in glucosinolate concentration and composition and the overall soil bacterial community changes is great importance for plant disease management. Fusarium wilt is one of the most serious disease on pepper. In this study, the influence of different BSMs which are from different brassicaceous species and hence differed in the glucosinolate content and composition: Camelina sativa ‘Crantz’ (CAME), Brassica juncea ‘Pacific Gold’ (PG), and a mixture of PG and Sinapis alba cv. ‘IdaGold’ (IG) (PG + IG, 1:1 ratio), on the bacterial community was investigated after the 25 days of soil incubation (pre-planting incubated soil) in the presence of Fusarium wilt pathogen and again after 35 days of pepper growth (post-planting rhizosphere soil). A soil treatment with no BSM amendment and comparable N, P, K addition level was used as control. The results showed that the content of 2-propenyl (allyl) glucosinolate, rather than 10-methy-sulfinyl-decyl-glucosinolate, contained in the seed meal, associated negatively with the plant disease index. All BSMs treatments significantly decreased the bacterial richness and diversity and altered the bacterial community structure after 25 days of incubation before planting. Only in the soil where the BSM was amended could the plant growth play a significant role in shaping the bacterial communities: the plant growth could help the bacterial communities to recover from disturbed state (in terms of the richness, diversity, and structure), resulting from seed meal treatment, to be more close to the original state although significant difference still existed (except the difference between CAEM and CK in the bacterial richness and diversity) between BSM-amended and un-amended rhizosphere soil. Close association between rhizosphere bacterial community and plant disease index was revealed not only at the overall bacterial community level but also at the specific bacterial population level: (1) at the overall bacterial community level, the more similar plant disease index were, the more close the rhizosphere bacterial community became in terms of the richness, diversity, structure, and interaction; and (2) at the course and finer taxonomic level for specific bacterial populations, the relative abundance of 2 phyla/classes and 7 genera were negatively correlated with plant disease index, with correlation being strongest in Streptomyces and the unclassified genus within Actinobacteria, while the relative abundance of 4 phyla/classes and 7 genera 5 unclassified genera revealed a positive correlation with plant disease index. Furthermore, it is intriguing that simpler bacteria interaction was found in the rhizosphere soil where the plant disease index was lower while relatively complex interaction was found in that where the plant disease was higher. This work is helpful for understanding the mechanisms that led to the contrasting plant disease severity under addition of different BSMs from the view point of microbiology.