Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/25/2004
Publication Date: 1/1/2005
Citation: Gillen, A.M., Bliss, F.A. 2005. Identification and mapping of markers linked to the Mi gene for root-knot nematode resistance in peach. Journal of the American Society for Horticultural Science. 130(1):24-33. Interpretive Summary: Root-knot nematode Meloidogyne incognita (race 1) infestation of peach tree roots lowers yields and shortens the lifespan of an orchard. Breeding for resistance to root-knot nematode M. incognita the most effective means to control this pest, is time consuming, destructive and labor intensive, but can be facilitated greatly through the use of molecular markers. However, molecular markers linked to most genes for resistance to root-knot nematode are not yet available. This study was conducted to confirm the monogenic nature of resistance of the Mi gene using a peach mapping population, to create a genetic linkage map using diverse molecular markers and to map the Mi gene. Genetic analysis indicated that a single major gene controls the resistance to M. incognita in this population and several tightly linked molecular markers were found. Comparison of common markers among published genetic linkage maps placed the Mi locus on Prunus linkage group 2. In addition, the mapping of Resistance Gene Analogs in this population will be of use to researchers who are interested in the location of resistance genes in Prunus. This information will be of great interest to plant pathologists, geneticists and peach rootstock breeders. It will facilitate the comparison of different sources of resistance to M. incognita and the pyramiding of different resistance genes into a single genotype. Identification of the map location of the Mi gene and closely-linked molecular markers solves a long-standing problem and should facilitate the genetic improvement of peach rootstocks worldwide.
Technical Abstract: An F2 population from a single F1 plant from the cross of peach [Prunus persica (L.) Batsch] rootstock cultivars Harrow Blood ('HB') x Okinawa ('Oki') was used to locate the Mi locus, which conditions resistance to Meloidogyne incognita (race 1) (Kofoid and White) Chitwood. These data and comparison of common markers among published genetic linkage maps placed the Mi locus on Prunus linkage group 2. Two restriction fragment length polymorphisms ('RFLPs') [linked at 4.8 and 6.8 centimorgan ('cM'), repulsion phase] and one random amplified polymorphic DNA ('RAPD') marker (linked at 9.5 cM, coupling phase) were linked to Mi. The RAPD marker was cloned, sequenced and converted to a polymerase chain reaction ('PCR')-based cleaved amplified polymorphic sequence ('CAPs') marker. Clones of resistance gene analogs ('RGA') developed from Oki were highly polymorphic when used as RFLP probes. The RGA's mapped to four linkage groups but clustered on two of the four linkage groups, providing limited coverage of the genome. Even so, they may be useful as markers for disease resistance genes that occur in other populations. The linkage maps of the HB x Oki F2 population and a peach x almond (Prunus amygdalus Batsch) F2 population were colinear in certain regions, however a significant number of markers mapped to different linkage groups among the two populations. The locus for the blood-flesh trait (red-violet mesocarp) mapped to the top of linkage group 4.