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Public concerns about crop uniformity introduced by modern plant breeding and genetic vulnerability to biotic and abiotic stresses have been one of the major forces driving long-term efforts in plant germplasm conservation for future food security. However, such concerns have gained little empirical support, as recent molecular diversity analyses of improved crop gene pools did not reveal much reduction from early to recent breeding efforts. We conducted a genome-wide examination of 75 Canadian hard red spring wheat (Triticum aestivum L.) cultivars released from 1845 to 2004 using 370 simple sequence repeat (or SSR) markers that were widely distributed over all 21 wheat chromosomes. A total of 2280 SSR alleles were detected. Allelic reduction occurred in every part of the wheat genome and a majority of the reduced alleles resided in only a few early cultivars. Significant allelic reduction started in the 1930s. Considering 2010 SSR alleles detected in the 20 earliest cultivars, 38% of them were retained, 18% were new, and 44% were lost in the 20 most recent cultivars. The net reduction of the total SSR variation in 20 recent cultivars was 17%. This clear-cut evidence not only supports the contention that modern plant breeding reduces the genetic diversity of Canadian wheat, but also underlies the need for conserving wheat germplasm and introducing genetic diversity into wheat breeding.

A male sterile wheat mutant, Triticum aestivum L. 'Taigu', was found in a wheat field in China in 1972. The male sterility was controlled by a single dominant gene that was referred to as Ms2. Recently, this gene was found to be linked to a dwarfing gene through crossing Taigu with the short wheat T. aestivum 'Ai-Bian 1' carrying the dwarfing gene Rht-D1c. The objective of this study was to develop molecular markers linked to the male sterility Ms2 gene in common wheat. One hundred and twenty-two near-isogenic lines were developed through backcrossing and sib intercrossing and used as the mapping population for the development of molecular markers. Bulked segregant analysis was used to screen 48 pairs of SSR primers, and a marker, MS2-WMC617, was identified closely linked to the male sterile Ms2 gene that mapped at the distal position of chromosome arm 4DS. The use of the molecular marker MS2-WMC617 can facilitate recurrent selection in a wheat breeding program based on marker-assisted selection. Key words: Triticum aestivum, male sterility, Ms2 gene, Rht-D1c gene, SSR marker. Un ble androsterile nomme Triticum aestivum L. 'Taigu' a ete trouve dans un champ de ble en Chine en 1972. L'androsterilite etait controlee par un seul gene dominant qui a ete nomme Ms2. Recemment, il a ete trouve que ce gene etait lie a un gene de nanisme en effectuant un croisement entre Taigu et le ble nain T. aestivum 'Ai Bian l', lequel porte le gene nanisant Rht-D1c. L'objectif de la presente etude etait d'identifier des marqueurs moleculaires lies au gene d'androsterilite Ms2 chez le ble tendre. Cent vingt deux lignees quasi-isogeniques ont ete produites par retrocroisement et croisement entre lignees sueurs. Cette collection de lignees a ete employee comme population de cartographie pour identifier des marqueurs moleculaires. Une analyse de segregants groupes (<< bulked segregant analysis >>) a ete utilisee pour cribler 48 paires d'amorces SSR et un marqueur, MS2-WMC617, a ete trouve etroitement lie au gene d'androsterilite Ms2, lequel est situe en position distale sur le bras chromosomique 4DS. L'emploi du marqueur MS2-WMC617 pourra faciliter la selection recurrente au sein d'un programme de selection faisant appel a la selection assistee de marqueurs. Mots-cles : Triticum aestivum, androsterilite, gene Ms2, gene Rht-D1c, marqueur SSR. [Traduit par la Redaction], Introduction In 1972, a male sterile wheat mutant, Triticum aestivum L. 'Taigu', was found in a wheat field in China by an agricultural technician (Gao 1987). At the flowering stage, [...]

Leaf rust (caused by Puccinia triticina Eriks.) is an important disease of wheat (Triticum aestivum L.) in North America. This study was conducted to assess the utility of the uncharacterized resistance gene Lr60 (formerly LrW2) for the development of resistant cultivars by demonstrating its novelty, genetic location, and the breadth of resistance that it confers. Haploids of a single gene line carrying Lr60 (RL6172) were pollinated with a susceptible cultivar to generate hybrids with random chromosome deficiencies arising from irregular meiosis of the haploid. Out of 488 hybrids, four were susceptible to leaf rust. All susceptible hybrids lacked several polymorphic microsatellite alleles from RL6172 that are specific to chromosome 1D. Analysis of an F2 population confirmed that Lr60 was located on the short arm of 1D, 8.4 cM distal to the microsatellite BARC149. Since Lr21 is also located on 1DS a cross was made between single gene lines of Lr21 and Lr60; five susceptible plants recovered in F2 out of 1141 individuals tested were confirmed with progeny tests. This ratio (5:1136) gives an estimated recombination frequency of 13% between Lr21 and Lr60. RL6172 was tested with 37 isolates of P. triticina, encompassing a diversity of virulence found in North America; one isolate was virulent. Lr60 is a novel resistance gene and represents a useful diversification of the genetic resources available in wheat for development of leaf rust resistant cultivars.

Abstract: Bread wheat and durum wheat were examined for linkage disequilibrium (LD) using microsatellite markers distributed across the genome. The allele database consisted of 189 bread wheat accessions genotytypd at [...]

Abstract: Triticum turgidum L var. durum is known to be particularly susceptible to infection by Fusarium graminearum, the causal agent for Fusarium head blight (FHB), which results in severe yield [...]

Lodging resistance is a key objective in pea breeding programs. Implementation of marker-assisted selection (MAS) in early generations could significantly enhance the efficiency of the breeding process compared with conventional selection in the [F.sub.3] or later generations. The objective of this research was to evaluate the effectiveness of MAS for lodging resistance using a combination of a coupling-phase linked marker A001 and a repulsion-phase linked marker A004 in [F.sub.2] generation field pea (Pisum sativum L.). Eight [F.sub.2] populations consisting of 680 plants were scored for the markers. A total of 402 [F.sub.3] families derived from MAS and 187 [F.sub.3] families from unselected populations were evaluated for lodging reaction under field conditions. The lowest lodging scores for each population were obtained from plants with the combination of A001 marker presence and A004 marker absence. A higher proportion of lodging resistant [F.sub.3] families was obtained from this marker combination as compared with phenotypic selection in the [F.sub.3] generation. MAS was less expensive than phenotypic selection in the field. Thus, A001 and A004 are useful for MAS for lodging resistance in early generation pea breeding populations., LODGING is usually referred to as a condition in which the stems of crops bend at or near the surface of the ground, which may lead to the collapse of [...]