Durability of resistance against fungal, bacterial and viral pathogens; present situation |
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Authors: | Jan E Parlevliet |
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Institution: | (1) Laboratory of Plant Breeding, Department of Plant Science, Wageningen University, P.O. Box 386, 6700 AJ Wageningen, The Netherlands |
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Abstract: | In evolutionary sense no resistance lasts forever. The durability of a resistance can be seen as a quantitative trait; resistances
may range from not durable at all (ephemeral, or transient) to highly durable. Ephemeral resistance occurs against fungi and
bacteria with a narrow host range, specialists. It is characterised by a hypersensitive reaction (HR), major gene inheritance and many resistance genes, which often occur
in multiple allelic series and/or complex loci. These resistance genes (alleles) interact in a gene-for-gene way with a virulence
genes (alleles) in the pathogen to give an incompatible reaction. The pathogen neutralises the effect of the resistance gene
by a loss mutation in the corresponding avirulence allele. The incompatible reaction is not elicited any more and the pathogenicity
is restored. The pathogens can afford the loss of many avirulences without loss of fitness. Durable resistance against specialised
fungi and bacteria is often quantitative and based upon the additive effects of some to several genes, the resulting resistance
being of another nature than the hypersensitive reaction. This quantitative resistance is present to nearly all pathogens
at low to fair levels in most commercial cultivars. Durable resistance of a monogenic nature occurs too and is usually of
a non-HR type. Resistance against fungi and bacteria with a wide host range, generalists, is usually quantitative and durable. Resistances against viruses are often fairly durable, even if these are based on monogenic,
race-specific, HR resistances. The level of specialisation does not seem to be associated with the durability of resistance.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | broad resistance durable resistance generalist hypersensitivity pathogen-specific resistance quantitative resistance race-specific resistance specialist |
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