Articles
GENETIC TRANSFORMATION FOR FIRE BLIGHT RESISTANCE IN APPLE
We are currently working with the Gala apple sports Royal Gala and Galaxy, and the M.26 apple rootstock (see paper in this volume by Borejsza-Wysocka et al. titled “Transformation of authentic M.26 apple rootstock for enhanced resistance to fire blight”). Much of our work thus far, has focused on evaluating the antimicrobial proteins, attacin E, the cecropin analogs, SB-37 and Shiva-1, and hen egg white and T4 lysozymes for their effect on fire blight resistance.
In the case of cecropin SB-37-transgenics, several lines have been identified that are significantly more resistant than the Royal Gala parent.
However, a similar level of resistance was found in SB-37- and vector-transgenic lines and there was a lack of correlation between detectable cecropin and field resistance suggesting that biological variation may be a major contributor to the observed resistance (see paper in this volume by Norelli et al. titled “Effect of cecropin-like transgenes on fire blight resistance”). When resistant lines fruit (1999–2000), progeny analysis will be used to conclusively determine transgene effects on resistance.
Similar results were obtained with hen egg white lysozyme (HEWL)-transgenics.
One of the Royal Gala HEWL-transgenic lines that has been identified as resistant in both field and greenhouse tests, fruited this year in the orchard.
The fruit were similar in appearance to those of non-tranformed Royal Gala parent trees grown in the same orchard.
To date, the best fire blight resistance has been observed with attacin-transgenics.
Growth chamber, greenhouse and field evaluation of attacin transgenic lines has shown significant increases in the fire blight resistance of some lines in specific tests.
In 1998 field trials, one attacin-line (T138) had only 5% shoot blight compared with approximately 60% in non-transgenic Royal Gala controls and approximately 40% in the moderately resistant Liberty controls.
The gene encoding T4 lysozyme is also being evaluated, expressed either singly or in combination with attacin E, for its effect in apple on resistance to Erwinia amylovora (see paper in this volume by Hanke et al. titled “Transformation of apple cultivars with T4-lysozyme-gene to increase fire blight resistance” and paper by Ko et al. titled “Effect of