Rootstock-regulated gene expression patterns associated with fire blight resistance in apple.

Area of Science:

• Plant pathology
• Plant genetics
• Molecular biology

Background:

• Apple trees are clonally propagated using scions grafted onto rootstocks.
• Rootstocks influence scion traits, including resistance to Erwinia amylovora (fire blight).
• Fire blight is a major bacterial disease affecting apple production.

Purpose of the Study:

• Quantify rootstock-mediated differences in scion fire blight susceptibility.
• Identify scion transcripts correlated with fire blight resistance.
• Investigate the genetic basis of rootstock-influenced disease resistance.

Main Methods:

• Orchard-grown 'Gala' apple trees on various rootstocks were inoculated with E. amylovora.
• Disease severity was assessed by measuring shoot necrosis over time.
• Gene expression analysis was performed using apple DNA microarrays.

Main Results:

• Significant differences in fire blight susceptibility were observed among rootstocks.
• 'Gala' scions on G.30 and MM.111 rootstocks showed lower necrosis rates than those on M.27 and B.9.
• 690 transcripts showed expression levels correlated with fire blight susceptibility; 39 were validated in a breeding population.

Conclusions:

• Rootstocks significantly influence 'Gala' scion susceptibility to fire blight.
• Rootstock-regulated gene expression patterns correlate with fire blight resistance.
• Potential roles for sorbitol dehydrogenase, phenylpropanoid metabolism, and protein processing in ER and endocytosis were suggested.