ARS | Publication request: Mapping QTL for Fusarium wilt Race 2 partial resistance in pea (Pisum sativum L.)

Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 17, 2011
Publication Date: January 9, 2012
Citation: Mcphee, K., Inglis, D., Gundersen, B., Coyne, C.J. 2012. Mapping QTL for Fusarium wilt Race 2 partial resistance in pea (Pisum sativum L.). Plant Breeding. pgs 1-7. doi:10.1111/j.1439-0523.2011.01938.x.

Interpretive Summary: Soil-borne root diseases of pea (Pisum sativum L.) cause significant crop loss annually. Fusarium wilt, caused by Fusarium oxysporum Schl. f. sp. pisi Snyd. and Hans. (Fop), is present worldwide in nearly all pea production regions (Kraft et al. 1981). Field symptoms appear as patches of dead or dying plants which gradually enlarge over time. Fusarium is a vascular pathogen that infects the plant root and establishes itself throughout the xylem tissue. Infected vascular tissue appears red and is diagnostic of Fusarium infection. Yield reduction can be considerable and the main control measures are to maintain long crop rotations and use resistant cultivars. The objectives of the current study were to 1) place the dominant gene, Fnw, on the Pisum genetic map, and 2) further characterize resistance to Fusarium wilt race 2 and discern the action of additional genetic factors on resistance. Genetic resistance to root diseases of pea are a primary objective of breeding programs worldwide. Resistance to race 2 has been incorporated into a number of released cultivars, especially in the fresh pea types, and is becoming more broadly incorporated into dry pea cultivars. Chromosomal location and identity of closely linked markers to Fnw will allow breeders and geneticists to identify resistant progeny through marker assisted selection methodology.

Technical Abstract: Fusarium oxysporum f.sp. pisi (Fop) is present in pea production regions worldwide, and causes a vascular wilt resulting in significant crop losses. Four races of Fop have been identified and resistance to each reportedly conferred by an individual single dominant gene. Fnw confers resistance to Fop race 2, which can be a serious pathogen for both green and dry pea production in the Pacific Northwest region of the U.S. The objective of this research was to place Fnw on the Pisum genetic map. A recombinant inbred line (RIL) population of 187 F7-derived lines from the cross ‘Shawnee’ / ‘Bohatyr’ was developed by single seed decent. All 187 RILs, the parents, and a set of race 2 pea differential entries were challenged-inoculated with Fop race 2 under controlled conditions in three experiments, each with two or three replications per entry. Disease reactions were recorded as percent diseased plants 10 to 14 days weeks post-inoculation, or at regular intervals through flowering or green pod harvest in order to capture progressive wilting over time, typical of Fop race 2, by calculating area under disease progress curve (AUDPC) values. Percent diseased plants placed the putative single gene Fnw on Pisum sativum linkage group IV with LOD scores ranging from 40.0 to 65.6 and a minor loci on LG III (LOD 3.97). AUDPC values allowed for the detection of an additional QTL on linkage group III with LOD score of 4.60. The presence of transgressive segregants in the population indicated that complementary genes were contributed by each parent, both of which showed intermediate reaction to Fop race 2. Results of this research provide a basis for marker assisted selection for the major Fwn loci in both green and dry pea breeding programs but additional research is necessary to fully characterize the complementary gene action governing resistance of two minor loci identified.