Mapping of Major Fusarium Head Blight Resistance from Canadian Wheat cv. AAC Tenacious

Fusarium head blight (FHB) is one of the most devastating wheat disease due to its direct detrimental effects on grain-yield, quality and marketability. Resistant cultivars offer the most effective approach to manage FHB; however, the lack of different resistance resources is still a major bottleneck for wheat breeding programs. To identify and dissect FHB resistance, a doubled haploid wheat population produced from the Canadian spring wheat cvs AAC Innova and AAC Tenacious was phenotyped for FHB response variables incidence and severity, visual rating index (VRI), deoxynivalenol (DON) content, and agronomic traits days to anthesis (DTA) and plant height (PHT), followed by single nucleotide polymorphism (SNP) and simple sequence repeat (SSR) marker genotyping. A high-density map was constructed consisting of 10,328 markers, mapped on all 21 chromosomes with a map density of 0.35 cM/marker. Together, two major quantitative trait loci for FHB resistance were identified on chromosome 2D from AAC Tenacious; one of these loci on 2DS also colocated with loci for DTA and PHT. Another major locus for PHT, which cosegregates with locus for low DON, was also identified along with many minor and epistatic loci. QTL identified from AAC Tenacious may be useful to pyramid FHB resistance

Rapid and targeted introgression of genes into popular wheat cultivars using marker-assisted background selection

A marker-assisted background selection (MABS)-based gene introgression approach in wheat (Triticum aestivum L.) was optimized, where 97% or more of a recurrent parent genome (RPG) can be recovered in just two backcross (BC) generations. A four-step MABS method was developed based on 'Plabsim' computer simulations and wheat genome structure information. During empirical optimization of this method, double recombinants around the target gene were selected in a step-wise fashion during the two BC cycles followed by selection for recurrent parent genotype on non-carrier chromosomes. The average spacing between carrier chromosome markers was <4 cM. For non-carrier chromosome markers that flanked each of the 48 wheat gene-rich regions, this distance was approximately 12 cM. Employed to introgress seedling stripe rust (Puccinia striiformis f. sp. tritici) resistance gene Yr15 into the spring wheat cultivar 'Zak', marker analysis of 2,187 backcross-derived progeny resulted in the recovery of a BC(2)F(2ratio3) plant with 97% of the recurrent parent genome. In contrast, only 82% of the recurrent parent genome was recovered in phenotypically selected BC(4)F(7) plants developed without MABS. Field evaluation results from 17 locations indicated that the MABS-derived line was either equal or superior to the recurrent parent for the tested agronomic characteristics. Based on these results, MABS is recommended as a strategy for rapidly introgressing a targeted gene into a wheat genotype in just two backcross generations while recovering 97% or more of the recurrent parent genotype

Comparison of cultivar ‘Zak’ derivatives carrying stripe rust resistance gene <i>Yr15</i> developed with (WA8059) and without (WA8046) MABS.

<p>(A) Graphical genotypes, showing parental derivation with green bars representing the homozygous RP alleles, red bars indicate the marker allele homozygous for DP, and heterozygous loci were marked with half green and half red bars. Orange star represents the carrier chromosome, with red arrow corresponding to the approximate position of the target gene (<i>Yr15</i>) on the carrier chromosome and blue dots denotes relative position of the SSR markers used for the comparison. (B) Comparison of various parameters recorded during field evaluation and quality analysis of these three lines done at different locations.</p

Proposed MABS strategy in wheat for introgressing a target gene while recovering 97% or more RPG in just two BCs.

<p>Proposed MABS strategy in wheat for introgressing a target gene while recovering 97% or more RPG in just two BCs.</p

Physical Locations of Genes/Markers, recombination (Rec.) in GRRs in Wheat Genome.

<p>This table is adapted from Erayman et al. 2004 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0005752#pone.0005752-Erayman1" target="_blank">[9]</a>.</p

Recurrent parent genome (RPG) recovery by MABS.

*<p>DPG: Donor parent genome; RP: Recurrent parent; DP: Donor parent.</p

Schematic representation of introgression of stripe rust resistance gene <i>Yr15</i> into the cultivar ‘Zak’ using MABS.

<p>Schematic representation of introgression of stripe rust resistance gene <i>Yr15</i> into the cultivar ‘Zak’ using MABS.</p

Strategy for selection of markers for marker-assisted backcross breeding program.

<p>Example is given for consensus chromosome of group 1. Names of the GRRs are provided on the right side of a consensus chromosome. In the nomenclature of GRRs (e.g. ‘1S0.8’), the first digit represents wheat homoeologous group followed by the arm location either as short arm (S) or long arm (L). The last two numeral numbers represent GRR location as fraction length (FL) of the chromosome (e.g. 0.8 for ‘1S0.8’). Along with GRRs the recombination in cM observed for particular GRRs is also given. On the left side of the consensus chromosome, * denotes the number of markers selected for a particular GRR region. Number of markers selected for each GRR was variable. For example the regions showing high recombination, like GRR 1L0.9, three markers were selected, two flanking and one from the middle of the GRR, whereas in the case of a GRR like 1S0.4, only two markers flanking the GRR was selected.</p

Polymorphism survey of ‘Zak’ and the <i>Yr15</i> gene donor line using SSR markers.

<p>Polymorphism survey of ‘Zak’ and the <i>Yr15</i> gene donor line using SSR markers.</p

Computer simulations to optimize MABS approach in wheat.

<p>(A–C) Plabsim results for RPG recovery at different Q-values including the minimum and maximum value using 110 (A), 208 (B) and 320 (C) markers for two-stage (red line), three-stage (green line) and four-stage (blue line) selection. (D–E) Represents %RPG recovered with increasing BC generation at constant population size of 100 per BC (D), and with constant increase in population size (E), using 110 (red line), 208 (blue lines) and 320 (pink lines) markers and four-stage selection strategy. Solid lines corresponds to Q_max values, whereas dotted lines represents Q_min values. (F–H) Corresponds to the number of MDP required in each generation using two- (red line), three- (green line) and four-stage (blue line) selection strategy for 208 (F), 110 (G) and 320 (H) markers. (I–K) Represents the Q_max (shaded bars) and Q_min values (solid bars) of RPG recovery in BC₁ (green bars) and BC₂ (red bars) generation using variable population size per BC and four-stage selection, and for 110 (I), 208 (J) and 320 (K) markers. Blue dots correspond to the number of MDPs required.</p