Manuela Nagel

The longevity of crop seeds stored under ambient conditions.

The ability of crop seeds to retain their viability over extended periods of uncontrolled temperature and/or relative humidity conditions has not been widely investigated, although this is an important issue for genebank management. We report here the response of 18 crop species to storage for up to 26 years at 20.3 ^ 2.38C and 50.5 ^ 6.3% relative humidity. Germination rates decreased in a sigmoid fashion, but the curve parameters were species characteristic. Pea, common bean and maize seeds retained their viability over the longest period (23, 21 and 19 years, respectively). In contrast, chive seeds survived for only 5 years and lettuce for 7 years. In addition to this interspecific variability, there were also indices for intraspecific variability, particularly in bean and chive seeds, just as in collard, lupin, poppy, wheat and maize seeds. A significant correlation was obtained between germination performance in the laboratory and seedling emergence following autumn sowing. Seeds in which oil was the major seed storage component were more short lived, whereas carbohydrates or proteins did not show an effect on seed longevity.

Genome-wide association mapping and biochemical markers reveal that seed ageing and longevity are intricately affected by genetic background and developmental and environmental conditions in barley

Globally, over 7.4 million accessions of crop seeds are stored in gene banks, and conservation of genotypic variation is pivotal for breeding. We combined genetic and biochemical approaches to obtain a broad overview of factors that influence seed storability and ageing in barley (Hordeum vulgare). Seeds from a germplasm collection of 175 genotypes from four continents grown in field plots with different nutrient supply were subjected to two artificial ageing regimes. Genome-wide association mapping revealed 107 marker trait associations, and hence, genotypic effects on seed ageing. Abiotic and biotic stresses were found to affect seed longevity. To address aspects of abiotic, including oxidative, stress, two major antioxidant groups were analysed. No correlation was found between seed deterioration and the lipid-soluble tocochromanols, nor with oil, starch and protein contents. Conversely, the water-soluble glutathione and related thiols were converted to disulphides, indicating a strong shift towards more oxidizing intracellular conditions, in seeds subjected to long-term dry storage at two temperatures or to two artificial ageing treatments. The data suggest that intracellular pH and (bio)chemical processes leading to seed deterioration were influenced by the type of ageing or storage. Moreover, seed response to ageing or storage treatment appears to be significantly influenced by both maternal environment and genetic background.

Genetic studies of seed longevity in hexaploid wheat using segregation and association mapping approaches

Genebanks are entrusted with the storage, preservation and distribution of crop germplasm. Seed longevity is an important character in this context, but little is known regarding its genetic basis, largely because it is so strongly influenced by non-genetic factors. Here we present the outcome of a genetic dissection of seed longevity in bread wheat. We applied both a standard quantitative trait locus analysis based on segregation from a biparental cross, and an association analysis using a germplasm panel to detect marker trait associations. The latter revealed more loci than the former. Some of the genomic regions identified are known to contain genes determining spike architecture or aspects of biotic and abiotic stress responses. The results open perspectives for identification of favourable longevity alleles and the more accurate prediction of seed longevity in cereal germplasm collections.

An association mapping analysis of dormancy and pre-harvest sprouting in wheat

Seed dormancy and pre-harvest sprouting are important traits in bread wheat. Bi-parental populations have permitted the identification of several genes/quantitative trait loci controlling these traits, mapping to various bread wheat chromosomes. Here, we report the use of association mapping to uncover the genetic basis of both traits in a panel of 96 diverse winter wheat cultivars to establish the presence of marker-trait associations on many chromosomes. Potential candidate genes were identified by studying the gene content of the chromosome bins into which the major marker trait associations mapped.

Seed longevity in oilseed rape (Brassica napus L.) - genetic variation and QTL mapping

Abstract Although oilseed rape has become one of the most important oil crops in Europe, little isknown regarding the viability of its seed under conditions of long-term storage. We reporthere an examination of oilseed rape seed longevity performed on a set of 42 accessionshoused at the German ex situ genebank at IPK, Gatersleben. A comparison of germinationbetween the accessions stored for 26 years showed that viability was in part genetically deter-mined, since it ranged between 42 and 98%. An attempt was made to define the genetic basisof viability by subjecting a mapping population of doubled haploids to three artificial ageingtreatments. Quantitative trait loci (QTL) were detected on six chromosomes: N6, N7, N8, N15,N16 and N18. The chromosomal locations of these QTL were compared with their syntenicregions in Arabidopsis thaliana in order to explore what genes might underlie genetic vari-ation for longevity. Keywords: Brassica napus L; ex situ genebank; quantitative trait loci; seed longevity; synteny

Genome-Wide Association Mapping of Anther Extrusion in Hexaploid Spring Wheat

In a number of crop species hybrids are able to outperform line varieties. The anthers of the autogamous bread wheat plant are normally extruded post anthesis, a trait which is unfavourable for the production of F1 hybrid grain. Higher anther extrusion (AE) promotes cross fertilization for more efficient hybrid seed production. Therefore, this study aimed at the genetic dissection of AE by genome wide association studies (GWAS) and determination of the main effect QTL. We applied GWAS approach to identify DArT markers potentially linked to AE to unfold its genetic basis in a panel of spring wheat accessions. Phenotypic data were collected for three years and best linear unbiased estimate (BLUE) values were calculated across all years. The extent of the AE correlation between growing years and BLUE values ranged from r = +0.56 (2013 vs 2015) to 0.91 (2014 vs BLUE values). The broad sense heritability was 0.84 across all years. Six accessions displayed stable AE >80% across all the years. Genotyping data included 2,575 DArT markers (with minimum of 0.05 minor allele frequency applied). AE was influenced both by genotype and by the growing environment. In all, 131 significant marker trait associations (MTAs) (|log10 (P)| >FDR) were established for AE. AE behaved as a quantitative trait, with five consistently significant markers (significant across at least two years with a significant BLUE value) contributing a minor to modest proportion (4.29% to 8.61%) of the phenotypic variance and affecting the trait either positively or negatively. For this reason, there is potential for breeding for improved AE by gene pyramiding. The consistently significant markers linked to AE could be helpful for marker assisted selection to transfer AE to high yielding varieties allowing to promote the exploitation of hybrid-heterosis in the key crop wheat.

Barley Seed Aging: Genetics behind the Dry Elevated Pressure of Oxygen Aging and Moist Controlled Deterioration

Experimental seed aging approaches intend to mimic seed deterioration processes to achieve a storage interval reduction. Common methods apply higher seed moisture levels and temperatures. In contrast, the “elevated partial pressure of oxygen” (EPPO) approach treats dry seed stored at ambient temperatures with high oxygen pressure. To analyse the genetic background of seed longevity and the effects of seed aging under dry conditions, the EPPO approach was applied to the progeny of the Oregon Wolfe Barley (OWB) mapping population. In comparison to a non-treated control and a control high-pressure nitrogen treatment, EPPO stored seeds showed typical symptoms of aging with a significant reduction of normal seedlings, slower germination, and less total germination. Thereby, the parent Dom (“OWB-D”), carrying dominant alleles, is more sensitive to aging in comparison to the population mean and in most cases to the parent Rec (“OWB-R”), carrying recessive alleles. Quantitative trait locus (QTL) analyses using 2832 markers revealed 65 QTLs, including two major loci for seed vigor on 2H and 7H. QTLs for EPPO tolerance were detected on 3H, 4H, and 5H. An applied controlled deterioration (CD) treatment (aged at higher moisture level and temperature) revealed a tolerance QTL on 5H, indicating that the mechanism of seed deterioration differs in part between EPPO or CD conditions.

Genetic architecture of seed longevity in bread wheat (Triticum aestivum L.)

The deterioration in the quality of ex situ conserved seed over time reflects a combination of both physical and chemical changes. Intraspecific variation for longevity is, at least in part, under genetic control. Here, the grain of 183 bread wheat accessions maintained under low-temperature storage at the IPK-Gatersleben genebank over some decades have been tested for their viability, along with that of fresh grain subjected to two standard artificial ageing procedures. A phenotype–genotype association analysis, conducted to reveal the genetic basis of the observed variation between accessions, implicated many regions of the genome, underling the genetic complexity of the trait. Some, but not all, of these regions were associated with variation for both natural and experimental ageing, implying some non-congruency obtains between these two forms of testing for longevity. The genes underlying longevity appear to be independent of known genes determining dormancy and pre-harvest sprouting.

Effects of Rht dwarfing alleles on wheat seed vigour after controlled deterioration

Abstract. Reduced height (Rht) alleles, commonly known as the ‘Green Revolution’ genes, have facilitated wheat breeding programs and achieved globally a more than 10% wheat yield increase. However, studies in barley indicate that shorter plant habits are associated with reduced seed vigour and longevity. Therefore, wheat seeds of six near-isogenic lines (NIL) carrying the dwarfing alleles Rht-B1b, Rht-D1b, Rht-B1c, Rht-B1b+-D1b, Rht-B1c+-D1b and the wild-type allele Rht-B1a+-D1a, each in four background cultivars, were stressed by controlled deterioration. Seed vigour expressed as root and shoot lengths, time to 50% (T50) and time between 16 and 84% (T16-84) germination showed significant changes after treatment. However, after controlled deterioration only a combination of Rht alleles highly affected T16-84 and T50, which followed the general pattern Rht-B1c+-D1b followed by > Rht-B1c > Rht-B1b+-D1b > Rht-B1b > Rht D1b = Rht-B1a+-D1a (wild type). Interestingly, only under control conditions seed vigour correlated positively with thousand-kernel weight, which decreased with severity of Rht type. Further, the seed length was not affected by the different NIL. In conclusion, NIL carrying combinations of Rht alleles tend to influence seed vigour, which could influence seed longevity. Therefore, plant breeders but especially genebank managers should consider that the genetic background of genotypes may affect seed deterioration processes, which could be an economically important aspect in future.

The genetic basis of durum wheat germination and seedling growth under osmotic stress

Durum wheat (Triticum turgidum L. var. durum) is mainly produced under rainfed but often sub-optimal moisture conditions in the Mediterranean basin. A set of 114 durum wheat recombinant inbred lines (RILs) developed from the cross of cultivars Omrabi5 × Belikh2 were tested for the ability to tolerate moisture deficiency at the germination and early seedling growth stage. The stress was imposed by exposing the germinating grain to 12 % polyethylene glycol. It induced a measurable reduction in root length, shoot length, and the percentage of normal seedlings. The germination and seedling growth of Belikh2 were more strongly inhibited than those of Omrabi5, and both parents were outperformed by > 50 % of the RILs. A quantitative trait locus (QTL) analysis was carried out by first assembling a linkage map from 265 informative microsatellites. Composite interval mapping revealed nine QTL spread over seven chromosomes. Five of these were associated with coleoptile length, and one of the five explained nearly 29 % of the relevant phenotypic variance. The coleoptile length was significantly correlated with the seedling growth, plant height, and thousand kernel mass derived from field-grown plants of the same RIL population.