Because of the huge size of the common wheat (Triticum aestivum L., 2n ϭ 6x ϭ 42, AABBDD) genome of 17,300 Mb, sequencing and mapping of the expressed portion is a logical first step for gene discovery. Here we report mapping of 7104 expressed sequence tag (EST) unigenes by Southern hybridization into a chromosome bin map using a set of wheat aneuploids and deletion stocks. Each EST detected a mean of 4.8 restriction fragments and 2.8 loci. More loci were mapped in the B genome (5774) than in the A (5173) or D (5146) genomes. The EST density was significantly higher for the D genome than for the A or B. In general, EST density increased relative to the physical distance from the centromere. The majority of EST-dense regions are in the distal parts of chromosomes. Most of the agronomically important genes are located in EST-dense regions. The chromosome bin map of ESTs is a unique resource for SNP analysis, comparative mapping, structural and functional analysis, and polyploid evolution, as well as providing a framework for constructing a sequence-ready, BAC-contig map of the wheat genome.

Marker-assisted breeding provides an opportunity for wheat breeders to introgress/pyramid genes of interest into breeding lines and to identify genes and/or quantitative trait loci in germplasm to be used as parents. Molecular markers were deployed to assist selection for disease resistance, agronomic and quality traits in several wheat cultivars released for commercial cultivation in Canada. Marker-assisted breeding is routinely used in most wheat breeding programmes for rust resistance (leaf, stem and stripe rust), orange wheat blossom midge resistance, high grain protein concentration, Fusarium head blight and common bunt resistance. Markers are being used selectively within breeding programmes to target traits that relate to market class or regional adaptation. For example, marker-assisted breeding for low lipoxygenase activity and low grain cadmium is being performed in durum breeding programmes and for enhancing stem solidness in programmes targeting resistance to the wheat stem sawfly. Markers are also being utilized for ergot resistance in durum wheat. Increased gluten strength is being selected with a marker for the overexpression of the Bx7 high-molecular-weight glutenin subunit. Marker-assisted breeding is also being used to pyramid resistance genes against a group of stem rust races related to TTKS (Ug99), a disease that poses a serious threat to global wheat production. Development of tightly linked diagnostic markers and high-throughput genotyping with SNP markers will result in more effective molecular wheat breeding in the near future and will open the door to genomic selection.

1129 RESEARCH M any wheat (Triticum aestivum L.) breeding objectives for organically managed systems (including grain yield, resistance to abiotic and biotic stresses, and baking quality) are similar to conventionally managed systems. It may be, however, necessary to test the expression of these traits under low input, very weedy organic conditions to maximize gain from selection in organic environments. A few traits relevant to high input farming may have negative effects on organic lands. The breeding for semidwarf wheat cultivars as a result of the green revolution has resulted in (i) reduced depth and size of root systems, (ii) increased reliance on N fertilizers to attain satisfactory protein content, (iii) ABSTRACT A randomly derived recombinant inbred line (RIL) population (n = 163) from a cross between CIMMYT spring wheat 'Attila' and the Canadian 'CDC Go' was used to map quantitative trait loci (QTL) affecting various agronomic and quality traits. The experiment was also designed to investigate the feasibility of organic wheat breeding by determining selection differentials and the effect of Rht-B1 in paired organic and conventional management systems. Heritability estimates differed between systems for five of nine traits measured; including grain yield, number of tillers, plant height, kernel weight, and grain protein content. Direct selection in each management system resulted in 50% or fewer selected individuals in common between the two systems, for eight of the nine (except for flowering time) studied traits. Most QTL were specific to either the organic or the conventional management system. However, consistent QTL for grain yield, grain volume weight, kernel weight, and days to flowering were mapped in both systems on chromosomes 6A, 1B, 3A, and 5B, respectively. The effect of Rht-B1 was more pronounced in organic systems, where RILs carrying the wild-type allele were taller, produced more grain yield with higher grain protein content, and suppressed weed biomass to a greater extent than those carrying dwarfing alleles. Results of the present study suggest that differences exist between the two management systems for QTL effects. Indirect selection of superior genotypes from one system to another will not result in the advancement of the best possible genotypes. Therefore, selection of spring wheat cultivars for organic systems should be conducted on organically managed lands.

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 ∼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 BC2F2∶3 plant with 97% of the recurrent parent genome. In contrast, only 82% of the recurrent parent genome was recovered in phenotypically selected BC4F7 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.

An 8-week feeding trial was conducted in flow through system to examine the effects of dietary supplementation of lysine and methionine on growth, nutrient utilization, haemato-biochemical status and carcass compositions in Indian major carp, rohu, Labeo rohita fingerlings (average weight 6.32 ± 0.06 g). Four experimental soy proteinbased diets D 0 (without lysine or methionine supplementation), D 1 (lysine supplementation alone), D 2 (methionine supplementation alone) and D 3 (both lysine and methionine supplementation) were fed to triplicate groups. L L-Lysine and DL DL-methionine were added to the diets containing 550 g kg )1 soybean meals at 4 and 7 g kg )1 of dry diet respectively. Significant higher weight gain, specific growth rate (SGR), protein efficiency ratio (PER), dry matter retention, nitrogen retention, total ash retention, whole carcass protein, haemoglobin concentration, haematocrit value, total erythrocytic count, total leucocytic count, plasma glucose and plasma total protein and lower FCR, per cent lipid retention and whole body moisture content were observed in fish fed soya protein-based diet supplemented with both lysine and methionine than that of fish of other dietary groups at the end of 8 weeks feeding trial. Although fish fed diet supplemented with either methionine or lysine did not show any significant differences of growth performances, feed utilization, carcass composition and haemato-biochemical status, fish of both of these dietary groups showed significantly better growth performances, feed utilization, carcass composition and haemato-biochemical status than that of fish fed diet without lysine and methionine supplementation. KEY WORDS