Articles
OBLIQUE RESISTANCE: THE HOST-PATHOGEN INTERACTION OF TOMATO AND THE BACTERIAL SPOT PATHOGEN
Article number
914_85
Pages
441 – 447
Language
English
Abstract
Plant resistance has been classically categorized as vertical or horizontal.
Vertical resistance is conferred by single R genes in the host that interacts with specific avirulence genes in the pathogen in a gene for gene manner.
The resistance may or may not be of a hypersensitive nature.
With horizontal resistance the resistance genes of the host do not have a differential interaction with the pathogen.
Generally horizontal resistance is thought to be conferred by multiple genes which are more durable than vertical genes since they are not overcome by emerging races of the pathogen.
However, there are numerous examples of vertical genes that have been effectively deployed for decades in intensive culture.
Other vertical genes are easily overcome by new races of the pathogen within a year or two of deployment.
Herein, we propose a third term for a resistance system; oblique resistance.
This term is used because it shares aspects of both vertical and horizontal resistance.
Oblique resistance is evident for tomato (Solanum lycopersicum) in response to bacterial spot (Xanthomonas spp.). For race T1, hypersensitive resistance from Hawaii 7998 was discovered but it was conferred by two or three genes as opposed to one gene that would be normal vertical resistance.
Moreover, hypersensitivity was necessary for a plant to have resistance in the field but other non-hypersensitivity genes were also required.
Before T1-resistant cultivars were deployed, race T3 emerged in Florida and overcame the quantitative resistance of Hawaii 7998. Resistance to race T3 was discovered in Hawaii 7981, an accession that was susceptible to race T1. Hawaii 7981 had race T3 hypersensitivity conferred by a single incompletely dominant gene, but resistance in the field also required other non-hypersensitive genes.
Before the deployment of T3 resistant cultivars, race T4 emerged and overcame the Hawaii 7981 resistance.
Elements of both vertical and horizontal resistance can be seen in this system.
Unfortunately, the horizontal aspects have not prevented the emergence of races virulent on existing resistance and breeders have not had the advantage of being able to more easily work with vertical genes.
Present breeding strategies include locating QTL associated with resistance across pathogen races and developing foliar tolerance where foliage does not blight after disease infection.
Vertical resistance is conferred by single R genes in the host that interacts with specific avirulence genes in the pathogen in a gene for gene manner.
The resistance may or may not be of a hypersensitive nature.
With horizontal resistance the resistance genes of the host do not have a differential interaction with the pathogen.
Generally horizontal resistance is thought to be conferred by multiple genes which are more durable than vertical genes since they are not overcome by emerging races of the pathogen.
However, there are numerous examples of vertical genes that have been effectively deployed for decades in intensive culture.
Other vertical genes are easily overcome by new races of the pathogen within a year or two of deployment.
Herein, we propose a third term for a resistance system; oblique resistance.
This term is used because it shares aspects of both vertical and horizontal resistance.
Oblique resistance is evident for tomato (Solanum lycopersicum) in response to bacterial spot (Xanthomonas spp.). For race T1, hypersensitive resistance from Hawaii 7998 was discovered but it was conferred by two or three genes as opposed to one gene that would be normal vertical resistance.
Moreover, hypersensitivity was necessary for a plant to have resistance in the field but other non-hypersensitivity genes were also required.
Before T1-resistant cultivars were deployed, race T3 emerged in Florida and overcame the quantitative resistance of Hawaii 7998. Resistance to race T3 was discovered in Hawaii 7981, an accession that was susceptible to race T1. Hawaii 7981 had race T3 hypersensitivity conferred by a single incompletely dominant gene, but resistance in the field also required other non-hypersensitive genes.
Before the deployment of T3 resistant cultivars, race T4 emerged and overcame the Hawaii 7981 resistance.
Elements of both vertical and horizontal resistance can be seen in this system.
Unfortunately, the horizontal aspects have not prevented the emergence of races virulent on existing resistance and breeders have not had the advantage of being able to more easily work with vertical genes.
Present breeding strategies include locating QTL associated with resistance across pathogen races and developing foliar tolerance where foliage does not blight after disease infection.
Publication
Authors
J.W. Scott, J.B. Jones , S.F. Hutton
Keywords
Lycopersicon esculentum, Solanum lycopersicum, Xanthomonas sp., horizontal resistance, vertical resistance, foliar disease, hypersensitive resistance
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