The effects of different disease-resistant cultivars of banana on rhizosphere microbial communities and enzyme activities

Rhizosphere Microbial Community and Metabolites of Susceptible and Resistant Tobacco Cultivars to Bacterial Wilt

Soil-borne diseases are closely related to rhizosphere microecosystem. While, plant species and genotypes are important factors affected rhizosphere microecosystem. In this study, the rhizosphere soil microbial community and metabolites of susceptible and resistant tobacco cultivars were investigated. The results showed that there were significant differences in the rhizosphere microbial community and metabolites between susceptible cultivar Yunyan87 and resistant cultivar Fandi3. Furthermore, the rhizosphere soil of Fandi3 showed a higher microbial diversity than that of Yunyan87. The abundance of R. solanacearum was much higher in the rhizosphere soil of Yunyan87 than in the rhizosphere soil of Fandi3, resulting in a higher disease incidence and index. While the abundance of beneficial bacteria in the rhizosphere soil of Fandi3 were higher than that of Yunyan87. Additionally, there were significant differences in metabolites between Yunyan87 and Fandi3 cultivars, and 4-hydroxybenzaldehyde, 3-hydroxy-4-methoxybenzoic acid, vamillic aldehyde, benzoic acid, 4-hydroxybenzyl alcohol, p-hydroxybenzoic acid and phthalic acid were notably high in Yunyan87. Redundancy analysis (RDA) indicated that the rhizosphere microbial community of Fandi3 and Yunyan87 were highly correlated with various environmental factors and metabolites. Overall, susceptible and resistant tobacco cultivars had different impact on rhizosphere microbial community and metabolites. The results expand our understanding of the roles of tobacco cultivars in plant-micro-ecosystem interactions, and provide a basis for the control of tobacco bacterial wilt.

A Comparison of Rhizospheric and Endophytic Bacteria in Early and Late-Maturing Pumpkin Varieties

To determine whether rhizospheric and endophytic bacteria contribute to the ripening of pumpkins, an analysis was conducted on rhizospheric and endophytic bacteria and soil fertility in the rhizospheres of early and late-maturing pumpkin varieties. The results showed higher nitrogen and abscisic acid content and more gibberellin-producing bacteria in the rhizospheres or endophytes of the early maturing varieties. Greater soil fertility and more abundant rhizospheric and endophytic bacterial genera with a greater metabolic function might be important mechanisms for early ripening. Rhodococcus, Bacillus, and Arthrobacter can be considered the functional bacteria in promoting pumpkin maturation. On the other hand, Ralstonia could be the functional bacterium that delays ripening.

Characterization of the microbial communities in wheat tissues and rhizosphere soil caused by dwarf bunt of wheat

Dwarf bunt of wheat, which is caused by Tilletia controversa J.G. Kühn, is a soil-borne disease which may lead up to an 80% loss of yield together with degradation of the quality of the wheat flour by production of a fishy smell. In this study, high-throughput sequencing technology was employed to characterize the microbial composition of wheat tissues (roots, spikes, first stem under the ear, and stem base) and rhizosphere soil of wheat varieties that are resistant and susceptible to T. controversa. We observed that the soil fungal community abundance and diversity were higher in resistant varieties than in susceptible varieties in both inoculated and uninoculated wheat, and the abundances of Sordariomycetes and Mortierellomycetes increased in the resistant varieties infected with T. controversa, while the abundances of Dothideomycetes and Bacteroidia increased in the susceptible varieties. Regarding the bacteria present in wheat tissues, the abundances of Chloroflexi, Bacteroidetes, Gemmatimonadetes, Verrucomicrobia and Acidobacteria in the ear and the first stem under the ear were higher than those in other tissues. Our results indicated that the abundances of Sordariomycetes, Mortierellomycetes, Leotiomycetes, Chryseobacterium and Massilia were higher in T. controversa-infected resistant varieties than in their controls, that Dothideomycetes, Bacteroidia, Nocardioides and Pseudomonas showed higher abundances in T. controversa-infected susceptible varieties, and that Curtobacterium, Exiguobacterium, Planococcus, and Pantoea may have higher abundances in both T. controversa-infected susceptible and resistant varieties than in their own controls.

Pathogenic Streptomyces spp. Abundance Affected by Potato Cultivars

Potato cultivars vary in their tolerance to common scab; however, how they affect common scab-causing Streptomyces spp. populations over time is poorly understood. This study investigated the effects of potato cultivar on pathogenic Streptomyces spp. abundance, measured using quantitative PCR, in three spatial locations in a common scab-infested field: (i) soil close to the plant (SCP); (ii) rhizosphere soil (RS); and (iii) geocaulosphere soil (GS). Two tolerant (Gold Rush, Hindenburg) and two susceptible cultivars (Green Mountain, Agria) were tested. The abundance of pathogenic Streptomyces spp. significantly increased in late August compared with other dates in RS of susceptible cultivars in both years. Abundance of pathogenic Streptomyces spp., when averaged over locations and time, was significantly greater in susceptible cultivars compared with tolerant cultivars in 2014. Principal coordinates analysis showed that SCP and RS soil properties (pH, organic carbon, and nitrogen concentrations) explained 68 and 76% of total variation in Streptomyces spp. abundance among cultivars in 2013, respectively, suggesting that cultivars influenced common scab pathogen growth conditions. The results suggested that the genetic background of potato cultivars influenced the abundance of pathogenic Streptomyces spp., with five to six times more abundant Streptomyces spp. in RS of susceptible cultivars compared with tolerant cultivars, which would result in substantially more inoculum left in the field after harvest.

Manure and mineral fertilization change enzyme activity and bacterial community in millet rhizosphere soils

Fertilization is a key agricultural practice for increasing millet yields and influencing soil properties, enzyme activities and rhizosphere bacterial communities. High throughput Illumina sequencing of the 16S rDNA was applied to compare the bacterial community structures and diversities among six different soil samples. The experiments involved the following: no fertilizer (CK), phosphate (P) and potassium (K) plus organic manure (M) (PKM), nitrogen (N) and K plus M (NKM), NPM, NPK and NPKM fertilization. The results showed that the NPKM fertilization of the millet field had a maximal yield of 3617 kg ha^-1 among the six different treatments. The abundances of the Actinobacteria and Bacteroidetes phyla, especially the Devosia, Mycobacterium, Opitutus and Chitinophaga genera, were higher in NPKM than those in the other samples. Redundancy analysis showed that the soil organic matter (SOM), available phosphorus (AP), and urease (UR) activity were significantly correlated with bacterial communities, while SOM and AP were strongly correlated with soil enzyme activities. Pearson's correlation showed that the available nitrogen was strongly correlated with Devosia and Mycobacterium, and SOM was strongly correlated with Opitutus and Chitinophaga. Besides, catalase was significantly related to Iamia, the UR was significantly related to Devosia, phosphatase was significantly related to Luteimonas and Chitinophaga. Based on the soil quality and millet yield, NPKM treatment was a better choice for the millet field fertilization practices. These findings provide a better understanding of the importance of fertilization in influencing millet yield, soil fertility and microbial diversity, and they lead to a choice of scientific fertilization practices for sustainable development of the agroecosystem.