Search

Re-examining historical datasets is a proposed use for association mapping (AM) and is particularly valuable when the data describes time-consuming and/or expensive to measure traits. A collection of 91 elite two-row malting barley (Hordeum vulgare L.) lines entered in the western Canadian Cooperative Two-Row Barley Trials over a 13- yr period were analyzed by AM to identify markers associated with seven malting quality traits. A linear mixed-model incorporating population structure and familial relatedness identified 27 diversity array technology (DArT) markers associated with malting quality. These markers will assist selection of parents with complementary allele combinations for future crosses and help identify progeny with the desired alleles. Putative candidate expressed sequence tags (ESTs) responsible for marker-trait associations were identified for 19 of the 27 DArT markers and include genes important for seed storage protein accumulation, gibberellin-mediated gene expression, seed storage mobilization, and dormancy. Efforts to identify novel variability in these genes may present opportunities to improve malting quality. doi: 10.2135/cropsci2009.06.0334

With the advancement of molecular marker technology and computer software, mapping quantitative trait loci (QTL) for complex traits in agricultural crops is frequent; however, exploitation of these QTL in practical breeding programs s limited. Here we report the validation of molecular markers linked to net blotch resistance QTL and their utilization in a barley (Hordeum vulgare L.) breeding program. Barley net blotch, caused by Pyrenophora teres Drechs. [anamorph: Drechslera teres (Sacc.) Shoemaker], is a serious foliar disease in Canada and other parts of the world. Simple sequence repeat (SSR) markers linked to net-form net blotch (NFNB) resistance QTL (QRpt6) and spot-form net blotch (SFNB) resistance QTL (QRpts4) were validated in two barley populations unrelated to the original mapping population. Marker-assisted selection (MAS) was performed with SSR markers to select resistant and susceptible lines in two other populations. The lines homozygous for the resistant-parent alleles at both marker loci had significantly lower infection than lines homozygous for the susceptible-parent alleles at both markers, indicating that MAS for net blotch resistance is practical. Since the major QTL, QRpt6, may provide adequate NFNB field resistance in western Canada, the plan for the Crop Development Centre (CDC) barley breeding program is to routinely utilize MAS for QRpt6 followed by normal field screening in disease nurseries to select the most resistant lines having additional resistance provided by less critical genes associated with other identified QTL. The CDC program has implemented routine MAS for QRpt6 and recommends this approach to other barley breeding programs. doi: 10.2135/cropsci2009.01.0011

Molecular marker technology shows potential to select and combine favorable alleles via genotypic selection and can be used to develop improved crop cultivars with considerable resource savings. In the present investigation, the utility of molecular markers for net blotch resistance identified in Australian breeding material was investigated for Canadian breeding material. Screening 42 Canadian, Australian, and international barley (Hordeum vulgare L.) lines with 10 Canadian Pyrenophora teres Drechs. isolates identified three lines resistant to all isolates evaluated. Net-form net blotch isolates were more virulent than spot-form net blotch isolates. The strong agreement between seedling and adult-plant reactions indicated that seedling screening could be useful for selection for adult-plant resistance. Evaluation of the inheritance of resistance in four Australian populations against Canadian P. teres isolates revealed one to three resistance genes, depending on the isolate used. The majority of Australian barley mapping population parents were susceptible to Canadian P. teres isolates, suggesting markers linked to their resistance may not be useful for Canadian breeding; however, some molecular markers identified by Australian workers could be used for Canadian barley breeding. This study demonstrates that the differences in germplasm and fungal pathogen strains used in different countries result in molecular markers that may not be applicable in all breeding programs for that crop.

Cowpea [Vigna unguiculata (L.) Walp] is an important grain legume crop grown for its protein rich grains. It is an inexpensive source of protein in the diets of people in sub-Saharan Africa. The International Institute of Tropical Agriculture (IITA) has been working on the improvement of cowpea for more than 30 yr. Over 60 countries receive cowpea cultivars improved by IITA for testing and adoption where needed. Many of these cultivars have identical parentage but look very different morphologically when grown in the field. Forty-six microsatellite DNA markers were used to evaluate genetic similarities among 90 cowpea breeding lines developed at IITA. Twenty-seven primer pairs could amplify polymorphic single-locus microsatellites from all of these materials. Two to seven alleles per primer were detected with a polymorphic information content varying from 0.02 to 0.73 By means of only five polymorphic microsatellite primers, 88 of the 90 cowpea lines could be distinguished. A dendrogram based on the microsatellite polymorphisms generally agreed with the pedigree of the cowpea lines., COWPEA is one of the world's important legume food crops. At least 12.5 million hectares of cowpea are cultivated with an annual production of over 3 million metric tons worldwide [...]

The genus Avena contains 30 different species from diploid through tetraploid to hexaploid with different genome compositions. Research regarding the origin of the different genomes in the polyploid species has been inconclusive. The objectives of this research were to investigate the phylogenetic relationships of the Avena species by means of polymorphisms in satellite, minisatellite, and microsatellite DNA. A satellite DNA sequence, ASS49, was isolated from a microsatellite-enriched library of the hexaploid oat Avena sativa L. Southern hybridization showed that ASS49 was a species-specific rather than a genome-specific satellite. ASS49 was able to distinguish species that may be the diploid and tetraploid progenitors of hexaploid oat. The phylogenetic relationship of Avena species was further investigated using 40 microsatellite and four minisatellite primers. These results appeared to support the findings with ASS49. It appears that the Ac-genome diploid species (A. canariensis Baum Raj. et Samp.) is the progenitor and A-genome donor of the hexaploid oat rather than the generally believed As-genome species (A. strigosa Schreber). Instead, A. strigosa appears to be a member of a separate lineage of diploid and tetraploid species including the tetraploid species A. abyssinica Hochst., THE GENUS Avena belongs to the Gramineae family. It contains 30 different species which form a distinct polyploid series ranging from diploid through tetraploid to hexaploid with a basic chromosome [...]

Applied Plant Biotechnology. Edited by V.L. CHOPRA, V.S. MALIK, and S.R. BHAT. Science Publishers Inc., P.O. Box 699, Enfield, NH 03748.1999. Hardback, 384 pp., $89.00. ISBN 1-57808-033-9. This book is [...]