BACKGROUND : Avocado (Persea americana Mill.) is a commercially important fruit crop worldwide. A major limitation
to production is the oomycete Phytophthora cinnamomi, which causes root rot leading to branch-dieback and tree
death. The decline of orchards infected with P. cinnamomi occurs much faster when exposed to flooding, even if
flooding is only transient. Flooding is a multifactorial stress compromised of several individual stresses, making
breeding and selection for tolerant varieties challenging. With more plantations occurring in marginal areas, with
imperfect irrigation and drainage, understanding the response of avocado to these stresses will be important for
RESULTS : Maintenance of energy production was found to be central in the response to flooding, as seen by
up-regulation of transcripts related to glycolysis and induction of transcripts related to ethanolic fermentation.
Energy-intensive processes were generally down-regulated, as evidenced by repression of transcripts related to
processes such as secondary cell-wall biosynthesis as well as defence-related transcripts. Aquaporins were found to
be down-regulated in avocado roots exposed to flooding, indicating reduced water-uptake under these conditions.
CONCLUSIONS : The transcriptomic response of avocado to flooding and P. cinnamomi was investigated utilizing
microarray analysis. Differences in the transcriptome caused by the presence of the pathogen were minor
compared to transcriptomic perturbations caused by flooding. The transcriptomic response of avocado to flooding
reveals a response to flooding that is conserved in several species. This data could provide key information that
could be used to improve selection of stress tolerant rootstocks in the avocado industry.