Host resistance - Genetics

12 important questions on Host resistance - Genetics

What relationship is described between plant species and resistance genes?

- A gene-for-gene relationship exists between plant species and resistance genes.
- Each plant species may possess several genes for resistance.

What is the role of R genes in plant-pathosystem interaction?

- R genes help protect the plant completely against the pathogen isolates carrying the corresponding Avr gene.

Which plant-pathosystem does not contain R genes according to the text?

- No R genes have been found in other plant-pathosystems such as groundnut and grape.
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What have studies on gene-for-gene relationship revealed about effector genes?

- Effector genes, conferring virulence, should occur in the pathogen if the plant-species has resistance genes.

How many loci are usually occupied by many loci in a plant?

- In each plant accession, usually only one locus is occupied by the functional resistance allele.

What is a rare occurrence in terms of pathogen genotypes and alleles for virulence?

- Pathogen genotypes with about 5 to 10 alleles for virulence are not particularly rare.

What is the focus of the I-2 locus, and where is it located?

- The I-2 locus is involved with resistance to Fusarium oxysporum f.sp. lycopersici.
- Located on chromosome 11 of tomato.

What does the presence of tandomly arranged multigene families of R genes indicate?

- It indicates the presence of many resistance genes within a few centimorgan distance on a chromosome.

What is speculated about the function of homologous nonfunctional genes found near resistance genes?

- They may arise from non-functional genes via mutation or recombination events.

What demonstrations come from the DNA sequence analysis of plant resistance genes?

- Unequal crossing over between the homologous complex loci.
- Evidence of past recombination between alleles in the I-2 and I-2D haplotypes.

What is the function of most alleles for resistance?

- Effective against specific genotypes of pathogen species.
- Different alleles work against different pathogen genotypes.

How does the presence of R genes within a race-specific distance affect plant resistance gene studies?

- It influences the selection of parental plants for genetic studies in plant resistance.

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