Seed conservation in ex situ genebanks - genetic studies on longevity in barley

Recognizing the danger due to a permanent risk of loss of the genetic variability of cultivated plants and their wild relatives in response to changing environmental conditions and cultural practices, plant ex situ genebank collections were created since the beginning of the last century. World-wide more than 6 million accessions have been accumulated of which more than 90% are stored as seeds. Research on seed longevity was performed in barley maintained for up to 34 years in the seed store of the German ex situ genebank of the Leibniz-Institute of Plant Genetics and Crop Plant Research in Gatersleben. A high intraspecific variation was detected in those natural aged accessions. In addition three doubled haploid barley mapping populations being artificial aged were investigated to study the inheritance of seed longevity. Quantitative trait locus (QTL) mapping was based on a transcript map. Major QTLs were identified on chromosomes 2H, 5H (two) and 7H explaining a phenotypic variation of up to 54%. A sequence homology search was performed to derive the putative function of the genes linked to the QTLs

Aegilops-Secale amphiploids: chromosome categorisation, pollen viability and identification of fungal disease resistance genes

The aim of this study was to assess the potential breeding value of goatgrass-rye amphiploids, which we are using as a “bridge” in a transfer of Aegilops chromatin (containing, e.g. leaf rust resistance genes) into triticale. We analysed the chromosomal constitution (by genomic in situ hybridisation, GISH), fertility (by pollen viability tests) and the presence of leaf rust and eyespot resistance genes (by molecular and endopeptidase assays) in a collection of 6× and 4× amphiploids originating from crosses between five Aegilops species and Secale cereale. In the five hexaploid amphiploids Aegilops kotschyi × Secale cereale (genome UUSSRR), Ae. variabilis × S. cereale (UUSSRR), Ae. biuncialis × S. cereale (UUMMRR; two lines) and Ae. ovata × S. cereale (UUMMRR), 28 Aegilops chromosomes were recognised, while in the Ae. tauschii × S. cereale amphiploid (4×; DDRR), only 14 such chromosomes were identified. In the materials, the number of rye chromosomes varied from 14 to 16. In one line of Ae. ovata × S. cereale, the U-R translocation was found. Pollen viability varied from 24.4 to 75.4%. The leaf rust resistance genes Lr22, Lr39 and Lr41 were identified in Ae. tauschii and the 4× amphiploid Ae. tauschii × S. cereale. For the first time, the leaf rust resistance gene Lr37 was found in Ae. kotschyi, Ae. ovata, Ae. biuncialis and amphiploids derived from those parental species. No eyespot resistance gene Pch1 was found in the amphiploids

Genetic Structure of Modern Durum Wheat Cultivars and Mediterranean Landraces Matches with Their Agronomic Performance

A collection of 172 durum wheat landraces from 21 Mediterranean countries and 20 modern cultivars were phenotyped in 6 environments for 14 traits including phenology, biomass, yield and yield components. The genetic structure of the collection was ascertained with 44 simple sequence repeat markers that identified 448 alleles, 226 of them with a frequency lower than 5%, and 10 alleles per locus on average. In the modern cultivars all the alleles were fixed in 59% of the markers. Total genetic diversity was HT = 0.7080 and the genetic differentiation value was GST = 0.1730. STRUCTURE software allocated 90.1% of the accessions in five subpopulations, one including all modern cultivars, and the four containing landrace related to their geographic origin: eastern Mediterranean, eastern Balkans and Turkey, western Balkans and Egypt, and western Mediterranean. Mean yield of subpopulations ranged from 2.6 t ha-1 for the western Balkan and Egyptian landraces to 4.0 t ha-1 for modern cultivars, with the remaining three subpopulations showing similar values of 3.1 t ha-1. Modern cultivars had the highest number of grains m-2 and harvest index, and the shortest cycle length. The diversity was lowest in modern cultivars (HT = 0.4835) and highest in landraces from the western Balkans and Egypt (HT = 0.6979). Genetic diversity and AMOVA indicated that variability between subpopulations was much lower (17%) than variability within them (83%), though all subpopulations had similar biomass values in all growth stages. A dendrogram based on simple sequence repeat data matched with the clusters obtained by STRUCTURE, improving this classification for some accessions that have a large admixture. landraces included in the subpopulation from the eastern Balkans and Turkey were separated into two branches in the dendrogram drawn with phenotypic data, suggesting a different origin for the landraces collected in Serbia and Macedonia. The current study shows a reliable relationship between genetic and phenotypic population structures, and the connection of both with the geographic origin of the landraces.The research was funded by the Ministerio de Economía y competitividad project AGL-2006-09226-C02-01, and Dr. Jose Miguel Soriano is funded by Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (http://www.mineco.gob.es/)

Physiological response of wheat seedlings to mild and severe osmotic stress

In the present study the physiological status of two wheat ( Triticum aestivum L.) cultivars subjected to polyethylene glycol-induced dehydration is evaluated. Wheat seedlings were exposed to either 8-d-long mild (15% PEG) or 24-h-long severe (30% PEG) osmotic stress by immersing their roots in PEG-supplemented Knop nutrient solution. Relative water content in the leaves and the levels of free proline, malondialdehyde, and hydrogen peroxide were chosen as indicative parameters corresponding to the degree of stress of the treated plants. Electrolyte leakage from leaf tissues of control and stressed plants was compared in terms of the common parameter Injury index used for characterizing cell membrane stability. In addition, a model test system was established for preliminary stress evaluation based on the kinetics of ion leakage. Short-term exposure to higher concentration of PEG was considered to be more harmful than prolonged mild stress as judged by RWC, proline and hydrogen peroxide accumulation, and injury index. The two cultivars demonstrated more obvious dissimilarities under conditions of prolonged mild stress than under severe stress

Characterization of two wheat doubled haploid populations for resistance to common bunt and its association with agronomic traits

Two segregating populations of doubled haploid (DH) wheat lines derived androgenetically from crosses ‘Svilena’ (susceptible) × A-38b-4-5-3-3 (highly resistant) and ‘Svilena’ × WWRN (moderately resistant to moderately susceptible) were characterized for resistance to common bunt. Disease incidence was evaluated after inoculation of seeds with a mixture of Tilletia foetida teliospores in two autumn sown field experiments. Two-gene model of inheritance of resistance in line A-38b-4-5-3-3 was suggested. The transgressive segregation in the latter population was indicative for a quantitative mode of inheritance. The DH lines were assessed for plant height, heading time and important yield components in a three-year field experiment without bunt infection. In both populations, transgressive segregation was observed for all agronomic characteristics. Although the disease incidence was positively correlated with most of the agronomic traits, genotypes combining bunt resistance with good yield potential were isolated from ‘Svilena’ × A-38b set of lines. These genotypes are valuable for breeding varieties designed for growing in low-input and organic farming systems. The two DH populations are suitable to be used for further studies on the genetic basis of bunt resistance

Frost tolerance in winter wheat cultivars: different effects of chromosome 5A and association with microsatellite alleles

Frost tolerance of ten Bulgarian winter wheat (Triticum aestivum L.) cultivars (Milena, Pobeda, Sadovo-1, Enola, Kristal, Laska, Svilena, Russalka, No301, and Lozen) and five foreign cultivars (Mironovskaya 808, Bezostaya-1, Rannaya-12, Skorospelka-35, and Chinese Spring) was studied in two experimental seasons following natural cold acclimation and in one experiment carried out in controlled acclimation conditions. Considerable intercultivar variability in plant survival was observed after freezing at -21 ºC following sufficient cold acclimation, or at -18ºC following insufficient or controlled acclimation. In seven cultivars, the effects of chromosome 5A on frost tolerance were investigated in their F2 hybrids with chromosome 5A monosomic lines of cultivars with high, intermediate, and low frost tolerance. The effects of chromosome 5A depended on the stress severity and the genetic background of the hybrids and varied even in cultivars of similar frost tolerance and vernalization requirements. Effects of other chromosomes besides 5A on frost tolerance were assumed. The analysis of six microsatellite loci located in the interval from centromere to Vrn-1 on chromosomes 5AL, 5BL, and 5DL showed that the major loci determining frost tolerance in Bulgarian winter wheats were Fr-A2 on chromosome 5AL and, to a lesser extent, Fr-B1 on chromosome 5BL. A strong association of the 176 bp allele at locus wmc327 tightly linked to Fr-A2 with the elevated frost tolerance of cvs. Milena, Pobeda, Sadovo-1, Mironovskaya-808, and Bezostay a-1 was revealed. Relatively weaker association between frost tolerance and the presence of the 172 bp allele at locus Xgwm639 tightly linked to Fr-B1 was also observed