Print PagePlants in natural and agricultural systems face severe threats due to pathogens and drought, which may interact to influence disease incidence and plant responses. The objective of this study was to understand factors influencing plant disease in natural systems and the genetic basis of drought and pathogen response.
Using natural, feral populations of the domesticated crop plant Brassica rapa and its pathogen Alternaria brassicae, we asked (1) What are the effects of soil moisture and drought on the distribution of A. brassicae infection in natural populations? (2) How do pathogens, drought and their interaction influence gene expression in B. rapa?
We sampled early and late in the growing season from 3 B. rapa populations in the western US. We analyzed the effects of soil moisture, plant stage and plant density on disease using general linear models.
To examine the effects of drought and pathogens on gene expression, we used microarray data generated by the Brassica rapa Genome Project. We analyzed this data using a local-pooled-error (LPE) test in R with a false discovery rate correction.
Results/Conclusions
We found that disease incidence was highest at the driest sites and in areas with more mature plants. In contrast, other studies have shown a direct correlation between moisture and disease incidence, as moisture aids in transmission and infection. It is possible that the condition of the host (in this case, drought weakened) may play a larger role in mediating disease than the environment’s direct effect on the pathogen.
We found 141 genes significantly differentially regulated in response to drought, 497 genes significantly differentially regulated in response to a plant pathogen, Pectobacterium carotovorum, and 50 genes that were differentially regulated in response to both drought and pathogen stress. All 50 of these genes were upregulated in response to stress. These findings are consistent with the hypothesis that there are shared stress response pathways to drought and pathogens in B. rapa. About half of the 50 drought/pathogen response genes had A. thaliana homologues that have previously been characterized as general stress response genes. Many of the genes have not been characterized in B. rapa or previously associated with stress response.
Taken together, the results of the study suggest that biotic and abiotic factors interact to influence disease incidence in natural populations, and plant responses to both disease and drought have a partially shared genetic basis.
