Molecular mapping of QTLs for resistance toGibberellaear rot, in corn, caused byFusarium graminearum

Abstract

Gibberella ear rot, caused by the fungus Fusarium graminearum Schwabe, is a serious disease of corn (Zea mays) grown in northern climates. Infected corn is lower yielding and contains toxins that are dangerous to livestock and humans. Resistance to ear rot in corn is quantitative, specific to the mode of fungal entry (silk channels or kernel wounds), and highly influenced by the environment. Evaluations of ear rot resistance are complex and subjective; and they need to be repeated over several years. All of these factors have hampered attempts to develop F. graminearum resistant corn varieties. The aim of this study was to identify molecular markers linked to the genes for resistance to Gibberella ear rot. A recombinant inbred (RI) population, produced from a cross between a Gibberella ear rot resistant line (CO387) and a susceptible line (CG62), was field-inoculated and scored for Gibberella ear rot symptoms in the F4, F6, and F7 generations. The distributions of disease scores were continuous, indicating that resistance is probably conditioned by multiple loci. A molecular linkage map, based on segregation in the F5 RI population, contained 162 markers distributed over 10 linkage groups and had a total length of 2237 cM with an average distance between markers of 13.8 cM. Composite interval mapping identified 11 quantitative trait loci (QTLs) for Gibberella ear rot resistance following silk inoculation and 18 QTLs following kernel inoculation in 4 environments that accounted for 6.7%-35% of the total phenotypic variation. Only 2 QTLs (on linkage group 7) were detected in more than 1 test for silk resistance, and only 1 QTL (on linkage group 5) was detected in more than 1 test for kernel resistance, confirming the strong influence of the environment on these traits. The majority of the favorable alleles were derived from the resistant parent (CO387). The germplasm and markers for QTLs with significant phenotypic effects may be useful for marker-assisted selection to incorporate Gibberella ear rot resistance into commercial corn cultivars.

Different Responses of Two Genes Associated with Disease Resistance Loci in Maize (Zea maysL.) to 3-allyloxy-1,2-benzothiazole 1,1-dioxide

“…Mapping population and statistic analysis PIC11 (Zmnbslrr1 anchored) was mapped by adding the RFLP and SCAR F5 segregation data was to the previous scores for RAPD, RFLP, SSR and SCAR markers for the individuals in the CG62 x CO387 RIL population (Ali et al, 2005) and reanalyzing linkages with MAPMAKER/ EXP version 3.0b (Lander et al, 1987) with the Kosambi mapping function (Kosambi, 1944). Linkage groups were identified using the "Group" command with a LOD score of 4.0 -6.0 and a recombination fraction of 0.4 (Ali et al, 2005).…”

“…Linkage groups were identified using the "Group" command with a LOD score of 4.0 -6.0 and a recombination fraction of 0.4 (Ali et al, 2005). The Zmnbslrr1 (PIC11) derived RFLP markers were added to existing linkage groups with the "Try" command.…”

“…The Zmnbslrr1 (PIC11) derived RFLP markers were added to existing linkage groups with the "Try" command. To determine the locations of the QTL on the map and estimate their phenotypic effects, composite interval mapping (CIM) was performed using QTL i88 Yuan et al Cartographer V2.0 (Wang et al, 2006;Ali et al, 2005). The chromosome orientations followed the Intermated B73 x Mo17 (IBM) maize map (Davis et al, 1999; http:// www.maizegdb.org) with the lowest bin positions at the top.…”

“…CO387, developed at Agriculture and Agri-Food Canada (AAFC, Ottawa, ON), has resistance to Gibberella ear rot following silk or kernel inoculation (Reid et al, 1994;Reid and Hamilton, 1996). This F 5 population was previously genotyped with 162 molecular markers and phenotyped for Gibberella ear rot disease in 4 environments, resulting in the identification of 18 QTL for resistance to F. graminearum (Ali et al, 2005). …”

“…The PCR conditions were as following: denaturation at 94ºC for 3 min, 35 cycles with denaturation at 94ºC for 30 s, annealing at 60-65ºC for 45 s, extension at 72ºC for 3 min and final hold at 10ºC. Following amplification, the samples were electrophoresed through 0.8 % (w/v) agarose gels, stained with 0.5 μg/ml ethidium bromide and visualized under UV light.Mapping population and statistic analysis PIC11 (Zmnbslrr1 anchored) was mapped by adding the RFLP and SCAR F5 segregation data was to the previous scores for RAPD, RFLP, SSR and SCAR markers for the individuals in the CG62 x CO387 RIL population (Ali et al, 2005) and reanalyzing linkages with MAPMAKER/ EXP version 3.0b (Lander et al, 1987) with the Kosambi mapping function (Kosambi, 1944). Linkage groups were identified using the "Group" command with a LOD score of 4.0 -6.0 and a recombination fraction of 0.4 (Ali et al, 2005).…”