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Identification of molecular markers linked to scab resistance and red colour in apple (Malus x domestica Borkh.). Supervisor

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Identification of molecular markers linked to scab resistance and red colour in apple (Malus x domestica Borkh.).

Supervisor: David Chagné

Project leaders: Susan Gardiner, Vincent Bus

Plant gene mapping group

Palmerston North research centre

Tennent drive

Private bag 11030

Palmerston North

New Zealand
Project rationale and objectives:
1/ Identification of markers linked to scab resistance
A considerable resource of major gene resistances to economically significant pests and diseases is available for apple breeders worldwide to use for marker-assisted selection of elite resistant seedlings from large breeding populations. Our New Zealand apple breeding programme at HortResearch has the goal of developing high quality new varieties possessing multiple durable resistances to a range of pests and diseases, such as apple scab (Venturia inaequalis). We expect that gene pyramiding (deployment of several resistance genes to a pest/disease in each new variety) will enhance the durability of the resistances we work with.
Our laboratory and breeding team has already developed molecular markers for 17 major resistance genes in apple and has been testing them for use in marker-assisted selection over the last 6 years. Breeding and team leader Vincent Bus has developed and phenotyped a number of populations segregating for further resistances. It is important for us in the associated Gene Mapping group to identify markers for as many of these new genes as feasible, in order to maximize the options of the breeding team to develop durably resistant new varieties.
2/ Identification of markers linked to red colour
Another key focus for the HortResearch apple breeding programme is the development of apple cultivars whose fruit combine novel flesh colours with excellent external appearance and eating quality. Active red-flesh breeding began in HortResearch in 1998 with the crossing of low quality red-fleshed accessions with high quality white-fleshed cultivars. Segregation data available for several crosses suggest a two gene control of red colour in apple. Candidate genes identified from HortResearch’s EST database were used to develop a molecular marker that was linked to one of these two genes, but no marker linked to the second gene has been discovered so far.

Work description
The student will work in collaboration with others in the Gene Mapping team using established methods to prepare DNA from leaves of individual seedlings. She will utilize this DNA together with information from prior phenotyping of the apple seedlings by apple breeders, to start to identify molecular markers linked to two genes: one conferring resistance to apple scab and one controlling red colour in the fruit. The student will be trained in use of our automated laboratory workstation, DNA extraction from apple leaves and in PCR analysis, as well as bioinformatics tools to develop markers from our 250,000 apple ESTs (Expressed Sequence Tags) database, and linkage mapping analysis software such as Joinmap v3.0.
Selected publications from the group:
Bus, V. G. M., P. A. Alspach, et al. (2002). "Genetic variability and preliminary heritability estimates of resistance to scab (Venturia inaequalis) in an apple genetics population." New Zealand Journal of Crop and Horticultural Science 30(2): 83-92.

Bus, V. G. M., F. N. D. Laurens, et al. (2005). "The Vh8 locus of a new gene-for-gene interaction between Venturia inaequalis and the wild apple Malus sieversii is closely linked to the Vh2 locus in Malus pumila R12740-7A." New Phytologist 166(3): 1035-1049.

Bus, V. G. M., E. H. A. Rikkerink, et al. (2005). "The Vh2 and Vh4 scab resistance genes in two differential hosts derived from Russian apple R12740-7A map to the same linkage group of apple." Molecular Breeding 15(1): 103-116.

Oraguzie, N. C., S. E. Gardiner, et al. (2001). "Genetic diversity and relationships in Malus sp. germplasm collections as determined by randomly amplified polymorphic DNA." Journal of the American Society for Horticultural Science 126(3): 318-328.

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