Validation of Molecular Markers for Use With Adapted Sources of Fusarium Head Blight Resistance in Wheat.

Genetic control of resistance to Fusarium head blight (FHB) is quantitative, making phenotypic selection difficult. Genetic markers to resistance are helpful to select favorable genotypes. This study was conducted to determine if Fhb1 and Fhb5 present in the Sumai 3 source of FHB resistance occur in Sumai 3-derived North American spring wheat cultivars and to understand the appropriateness of using markers to select for the favorable alleles at these loci in breeding. Sumai 3-derived parents Alsen, ND3085, ND744, Carberry, and Glenn were used in crosses to generate 14 doubled haploid breeding populations. The parents and progeny were genotyped with five Fhb1 and three Fhb5 microsatellite markers. Progeny were selected based on performance relative to parents and other control cultivars in FHB nurseries near Portage la Prairie and Carman, MB. χ2 and t test analyses were performed on marker and FHB data. The χ2 test frequently determined the proportion of lines carrying molecular variants associated with FHB resistance increased following nursery selection for FHB. Similarly, the t test regularly demonstrated that selection for FHB resistance lowered the mean level of disease associated with resistant marker haplotypes. The study affirmed FHB resistance sources Alsen, Carberry, ND3085, and ND744 have Fhb1 and Fhb5 loci like Sumai 3, but no evidence was found that Glenn carries Fhb1 and Fhb5 resistance alleles. The results justified use of Fhb1 and Fhb5 markers for marker assisted selection in populations derived from Alsen, Carberry, ND3085, and ND744, but not Glenn. Combined or individual application of Xgwm493 and Xgwm533 in selection of genotypes carrying Fhb1, and Xgwm150, Xgwm304, and Xgwm595 for Fhb5 will enhance FHB resistance in wheat.

Amino acid and fiber digestibility, intestinal bacterial profile, and enzyme activity in growing pigs fed dried distillers grains with solubles-based diets.

The aim of this study was to determine ileal AA and fiber digestibility in new-generation dried distillers grains with solubles (DDGS) derived from wheat (wDDGS), a wheat-corn blend [wcDDGS, wheat and corn were fermented in a 7:3 wt/wt ratio], or corn (cDDGS) and to determine the effects of diets containing DDGS on gut bacteria and bacterial and digestive enzyme activities. Experimental diets contained one of the DDGS samples as the sole source of protein, and a low protein diet (5% casein) was included to estimate basal endogenous ileal CP and AA losses. Chromic oxide (0.3%) was added as an indigestible marker to all diets. Twelve cannulated barrows with an initial BW of 20.2 +/- 1.3 kg were allotted to the 4 experimental diets in a 2-period crossover design, which provided 6 observations per diet. Pigs were acclimatized to their diets for 5 d followed by a continuous 12-h digesta collection on d 6 and 7. Diet had no effect on the apparent ileal digestibility (AID) of CP (P = 0.58). The wDDGS diet generally had decreased (P < 0.05) AID of AA compared with the wcDDGS or cDDGS diet. Similarly, the values for standardized ileal digestibility of CP and most AA were smaller (P < 0.05) for the wDDGS diet compared with the other 2 DDGS diets. The Lys and Thr were the least digestible AA among the indispensable AA across the 3 DDGS samples. The digestibilities of nonstarch polysaccharides and NDF were not affected by diet (P = 0.80 and 0.40, respectively); however, the ileal digesta viscosity was greater (P < 0.05) for the wcDDGS diet than the wDDGS and cDDGS diets. The counts of Lactobacillus (P = 0.09) and Enterobacteriaceae (P = 0.05) were greater for the cDDGS diet compared with the other 2 diets. Accordingly, the cDDGS diet elicited a greater (P < 0.05) lactic acid concentration in digesta than the wDDGS diet. The activities of bacterial (P = 0.86 to 0.91) and digestive enzymes (P = 0.31 to 0.80) did not differ among the diets. The results indicate that the wDDGS had generally less protein and AA ileal digestibilities compared with the wcDDGS and cDDGS samples and that nonstarch polysaccharides and NDF digestibilities were similar among diets. Although diet influenced digesta bacterial counts, no effects were observed on the activities of bacterial and digestive enzymes.

Chromosomal location of a race-specific resistance gene to Mycosphaerella graminicola in the spring wheat ST6.

Septoria tritici blotch, caused by Mycosphaerella graminicola, is a serious foliar disease of wheat worldwide. Qualitative, race-specific resistance sources have been identified and utilized for resistant cultivar development. However, septoria tritici blotch resistant varieties have succumbed to changes in virulence of M. graminicola on at least three continents. The use of resistance gene pyramids may slow or prevent the breakdown of resistance. A clear understanding of the genetics of resistance and the identification of linked PCR-based markers will facilitate the recovery of wheat lines carrying multiple septoria tritici blotch resistance genes. The resistance gene in ST6 to isolate MG2 of M. graminicola was mapped with microsatellite markers in two populations, ST6/Erik and ST6/Katepwa. Bulk segregant analysis identified a marker on chromosome 4AL putatively linked to the resistance gene. A large linkage group was identified in each population using additional microsatellite markers mapping to chromosome 4AL. The resistance gene in ST6 mapped to the distal end of chromosome 4AL in each mapping population and was designated Stb7. Three of the microsatellite loci, Xwmc313, Xwmc219 and Xgwm160, mapped within 3.5 cM of Stb7; however, none flanked Stb7. Xwmc313 was the closest and mapped 0.3 and 0.5 cM from Stb7 in the crosses ST6/Katepwa and ST6/Erik, respectively. WMC313 will be very useful for marker-assisted selection of Stb7 in Canadian breeding programs because the ST6 allele of Xwmc313 was not identified in any of the Canadian common wheat cultivars tested.

Inheritance of Race-Specific Resistance to Mycosphaerella graminicola in Wheat.

ABSTRACT Mycosphaerella graminicola causes Septoria tritici blotch of hexaploid and tetraploid wheat. The inheritance of high-level resistance to Septoria tritici blotch was studied in controlled environment experiments. Intraspecific reciprocal crosses were made between hexaploid wheat lines Salamouni, ST6, Katepwa, and Erik, and the tetraploid wheat lines Coulter and 4B1149. Parental, F(1), F(2), F(3), BC(1)F(1), and BC(1)F(2) populations were evaluated for reaction to isolates MG2 and MG96-36 of M. graminicola. Resistance was controlled by incompletely dominant nuclear genes in all cases. Salamouni had three independent resistance genes to isolate MG2, two of which also controlled resistance to isolate MG96-36. ST6 had a single resistance gene to isolate MG2 and none to isolate MG96-36. The resistance genes in Salamouni and ST6 were not allelic. Two independent genes control resistance to isolate MG2 in Coulter, one of which also controlled resistance to isolate MG96-36. These data are consistent with a gene-for-gene interaction in the wheat-M. graminicola pathosystem.

Identification of RAPD markers for percent hull in oat.

Percent hull is an important physical parameter of oat grain quality, but it is affected by environment. Multiple time-consuming evaluations are required to obtain a correct determination of phenotype. The application of marker-assisted selection for the genes involved would greatly simplify the identification of desirable oat genotypes. Bulked segregant analysis, with selected progeny lines derived from a cross between Cascade and AC Marie (30 and 23% hull, respectively), was used to identify randomly amplified polymorphic DNA markers linked to genetic factors controlling primary kernel hull percentage in oat. Twelve polymorphisms, identified between bulks, were tested for linkage to genetic factors controlling hull percentage by genotyping 80 randomly selected F2-derived F8 lines from the progeny population. Three markers showed significant test statistics for quantitative trait locus effects, when tested with primary kernel percent hull data from two environments. Together, the unlinked marker loci OPC13800, OPD20600, and OPK71300 explained approximately 41% of the genetic variance in primary kernel percent hull, after accounting for the main effect of environment.

A gene for resistance to a necrosis-inducing isolate of Pyrenophora tritici-repentis located on 5BL of Triticum aestivum cv. Chinese Spring.

Several sources of high-level resistance to tan spot caused by Pyrenophora tritici-repentis have been identified in hexaploid wheat (Triticum aestivum L.). This study was conducted to determine the number and chromosome location of a gene(s) in the cultivar Chinese Spring (CS) that confers resistance to a tan necrosis inducing isolate (nec+chl−) of P. tritici-repentis, 86-124, and insensitivity to Ptr necrosis toxin. Reciprocal crosses were made between CS (resistant-insensitive) and 'Kenya Farmer' (KF) (susceptible-sensitive). Analysis of the CS/KF F1and F2 populations and F2-derived F3 families identified a single nuclear recessive gene governing resistance to isolate 86-124 and Ptr necrosis toxin. Evaluation of the CS(KF) substitution series, F2 monosomic analysis, and screening of a series of 19 CS compensating nullitetrasomic and two ditelosomic lines (2AS and 5BL) indicated that the resistance gene was located on chromosome arm 5BL. No linkage exists between Lr18 and the tan necrosis resistance gene on chromosome arm 5BL. It is proposed that the gene for resistance to the tan necrosis inducing isolate 86-124 (nec+chl−) of P. tritici-repentis and Ptr necrosis toxin be named tsn1. Key words : wheat, Triticum aestivum L., tan spot resistance, Pyrenophora tritici-repentis (Died.) Drechs., chromosome location, Ptr necrosis toxin.

An integrated approach to oilseed rape cultivar selection using phenotypic stability.

Various methods of evaluating phenotypic stability have been proposed; however, no single method can adequately describe cultivar performance. The objectives of this study were to integrate a number of methods of evaluating stability and to use this approach for cultivar selection. These objectives were considered in the context of the broad-based oilseed rape cultivar (Brassica napus spp. oleifera) evaluation system currently used in western Canada. Regression analysis was used to assess cultivar response to environments. Cluster analysis was used to assemble cultivars into groups with similar regression coefficients (b i ) and mean yield. Three parametric stability parameters, years within locations mean square (MS; Y/L), Shukla's stability variance (σ i (2) ), and Francis and Kannenberg's coefficient of variability (CV i ), were compared to determine which method would be most suitable for selection of oilseed rape cultivars from within clustered groups. Yield data from three cultivars and six breeding lines that had been tested for 2 years at 26 locations in the Western Canola Cooperative Test 'A' were used for all calculations. The cluster analysis was successful in identifying commercially acceptable breeding lines. The parameter MS i Y/L was considered to be more appropriate than either CV i or σ i (2) , because it measured only the unpredictable portion of the genotype x environment interaction and was independent of the other cultivars in the test. The use of cluster analysis to group entries with similar b i values and mean yields, followed by selection for stability within groups, was advocated.