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Title: Nitrogen stress reduces fungal pathogen symptoms and dampens the correlation between disease and early-season bacterial epiphyte diversity in maize

Author
item MANCHING, HEATHER - University Of North Carolina
item Balint-Kurti, Peter
item STAPLETON, ANN - University Of North Carolina

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2014
Publication Date: 7/29/2014
Citation: Manching, H.C., Balint Kurti, P.J., Stapleton, A.E. 2014. Nitrogen stress reduces fungal pathogen symptoms and dampens the correlation between disease and early-season bacterial epiphyte diversity in maize. Frontiers in Plant Science. doi: 10.3389/fpls.2014.00403.

Interpretive Summary: An experiment was performed to examine the effects of multiple stresses - disease, lack of fertilizer and drought- singly and in combination on plant growth. In addition the diversity of phylosphere organisms was assessed under these various conditions. Different combinations of stresses appeared to have different effects on plant traits and phyloplane microbial diversity.

Technical Abstract: Plant leaves are inhabited by a diverse group of microorganisms that are important contributors to optimal growth. Environment effects on growth are usually studied in controlled setting using single factors and in field settings with large numbers of differences. Multi-factor combinations of stresses have the potential to bridge this gap and thus increase our mechanistic understanding of stress responses. We previously examined the relationship between bacterial diversity and pathogen resistance in Zea mays L. and proposed that the presence of certain species of bacteria on corn leaves could increase resistance to fungal infection. In this study we have examined how microbial communities changed when the plants and their epiphytes were exposed to multiple biotic and abiotic stresses and how correlations between microbial community structure and plant growth traits and resistance to fungal disease change with environmental stress. The maize inbred B73 line was exposed to single and combination abiotic and biotic stress treatments: low nitrogen, drought and infection with southern leaf blight (Cochliobolus heterostrophus). Microbial epiphyte samples were collected at the vegetative early-season phase and species composition was determined using 16S ribosomal intergenic spacer analysis. Cob diameter, plant height, seed weight, and resistance to southern leaf blight were measured at the end of the season. Plant traits showed the expected decreases in the stress treatments, though with nonlinear effects in combinations of stresses. Microbial species diversity was different among treatment groups (P< 0.001) and diversity was positively correlated with resistance to southern leaf blight. While no single microbial species had a large protective effect, small sets of species were good predictors of pathogen resistance levels. Leaf microbial diversity was scored much earlier in the season than plant resistance and plant growth, thus supporting use of this metric for prediction of plant productivity under disease pressure provided environmental quality is optimal.