Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2007
Publication Date: 5/1/2007
Citation: Niu, C., Hinchliffe, D.J., Cantrell, R.G., Wang, C., Roberts, P.A., Zhang, J. 2007. Identification of Molecular Markers Associated with Root-Knot Nematode Resistance in Upland Cotton. Crop Science. 47:951-960. Interpretive Summary: The root-knot nematode (RKN) is a major pest throughout the cotton growing belt in the United States. Direct losses due to RKN infestation are estimated to be in the millions of dollars annually. Cotton yield losses vary from state to state, but total Beltwide losses in 2007 due to RKN damage were 256,079 bales of cotton, which ranked highest among yield losses due to diseases, and represented an approximately 3% cotton yield reduction. RKN damage to cotton root systems also increases the susceptibility to fungal pathogens such as Fusarium wilt, indirectly resulting in even greater yield loss. Currently, no commercial Upland cotton cultivars exhibit significant resistance to RKN, however, resistant cotton lines have been developed. Despite the existence of RKN resistant cotton lines, transfer of the resistance trait into commercially important cotton cultivars is difficult due to the lack of a reliable and cost-efficient RKN screening method that distinguishes resistant from susceptible plants. The identification of the RKN resistance gene, or molecular markers closely linked to the resistance gene will greatly facilitate plant selection and allow the RKN resistance trait to be moved into commercially important cotton varieties. Utilizing three pairs of nearly genetically identical resistant and susceptible cotton lines and molecular marker screening techniques, seven DNA markers were found to be present or absent between the resistant and susceptible lines. One of the RKN markers that represented random DNA in the cotton genome was successfully converted into a DNA sequence-specific marker. Three of the newly developed DNA markers mapped to a region close to the presumed Upland cotton RKN resistance gene.
Technical Abstract: Cotton breeding for resistance to root-knot nematode (RKN) [Meloidogyne incognita (Kofoid and White) Chitwood] is hindered by the lack of convenient and reliable screening methods for resistant plants. The identification of molecular markers closely linked to RKN resistance will facilitate the development of RKN resistant cultivars through marker-assisted selection (MAS). Our objective was to identify and develop new DNA markers that are associated with RKN resistance in cotton. Using three pairs of nearisogenic (NIL) resistant (R) and susceptible (S) lines, two AFLP markers, two RAPD markers, and three RGA markers were identified to be polymorphic between the NIL-R and NIL-S lines. One RAPD marker was converted into a sequence-tagged site (STS) marker. In an F2 population of ‘ST 474’ × ‘Auburn 634 RNR’, the two RAPD markers and the STS marker were mapped to the same linkage group containing several markers that were previously reported to be linked with the RKN resistance gene rkn1 on chromosome 11 in ‘Acala NemX’. All these markers were found to be associated with a major RKN resistance gene, presumably Mi2 in the resistant line Auburn 634 RNR, suggesting that rkn1 and Mi2 are either allelic or closely linked. In addition, no susceptible recombinants were found in a resistance screen of 200 F2 plants from the cross Acala NemX × Auburn 634 RNR. The utility of the two RAPD markers and the converted STS marker were evaluated using 23 R and 8 S germplasm lines. The RAPD and STS markers, along with other previously reported markers associated with RKN resistance will be useful in germplasm screening, MAS for RKN resistance, and map-based cloning for RKN resistance genes.