Wild wheat (Triticum aestivum L.) relatives could represent a valuable source of genetic variation for improvement of abiotic stress tolerance in cultivated wheat. A better knowledge of the adaptive strategies developed by these species is needed. A collection of 157 Aegilops geniculata accessions originating from different ecogeographical regions was studied during two successive years for several traits related to water status, chlorophyll content, and plant thermal regulation under Mediterranean field conditions. Close association was found between the studied traits and the origin of accessions. Two adaptive strategies were distinguished. Accessions originating from harsh environments had low biomass, low grain production and high water‐use efficiency (low C isotope discrimination). They were early, with small, thick leaves exhibiting low chlorophyll content, high surface temperature and low epidermal transpiration. We suggest that in these accessions, decreased leaf chlorophyll content could limit the energy load from strong sunlight. In accessions originating from regions with a mild Mediterranean climate, thermal regulation of the leaf may rather depend on transpiration, as suggested by high C isotope discrimination values. These accessions also were characterized by high chlorophyll content, leaf area, and biomass production. Associations between the physiological traits observed could help to better understand the relationship between abiotic stress tolerance and yield in cultivated wheats. Results obtained confirmed the potential value of Aegilops geniculata for improvement of high temperature and drought stress tolerance in wheat and could contribute to the choice of traits to be introgressed and the accessions to be used in wide hybridization programs.
In Europe, wild wheat relatives of the Triticum–Aegilops complex grow in sympatry with cultivated bread wheat (Triticum aestivum L.) and spontaneous hybridization is known to occur. With the development of transgenic wheat, an understanding of the likelihood and occurrence of hybridization and introgression between wheat and its relatives is needed for use in risk assessment. To assess the probability of wheat to wild relative gene introgression, the distribution and biology of wheat wild relatives and their genome affinity and crossability with bread wheat were reviewed. Twelve of the 22 known Aegilops species, as well as one wild Triticum species, T. monococcum L. subsp. aegilopoides (Link) Thell., are known to occur in Europe near or within wheat cultivation. Five tetraploid species, Ae. cylindrica Host., Ae. triuncialis L., Ae. geniculata Roth., Ae. neglecta Req. ex Berthol., and Ae. biuncialis Vis., have wide distribution in most European countries. Bread wheat, wild Aegilops species, and Triticum species are predominantly autogamous (except Ae. speltoides Tausch, typically allogamous), but outcrossing among species is possible depending on species sympatry, concurrent flowering, and sexual compatibility. Spontaneous hybridization with wheat was reported for most of the tetraploid Aegilops species. The probability of gene transfer and gene retention in hybrid progenies is, however, higher when a gene is located on a shared genome, particularly on the D genome shared with Ae. cylindrica and Ae. ventricosa Tausch. Case‐by‐case and region‐by‐region assessments are needed to evaluate the risk associated with production and competitiveness of hybrids and their progeny.
SUMMARYDrought strongly affects cereal yield in several regions of the world. Plant growth and plant water status in response to soil water deficit play an important role in tolerance to drought and in yield stability. In order to investigate the relationship between plant growth and w^ater relations, 187 barley {Hordeum vulgare L.) recombinant inbred lines from a cross between two Mediterranean varieties, Tadmor and Fr/Apm, were studied in a growth chamber for RWC , number of leaves on the main tiller (NL), number of tillers (NT) and total shoot fresh and dry biomass (TSFM and TSDM). Measurements were made at the beginning of tillering on well watered plants and at a soil moisture content of 14% of field capacity. A negative phenotypic correlation between RWC and growth parameters was obtained in both treatments. Under water stress, a negative genetic correlation was also found between the same characters. QTLs involved in RWC, NL and TSFM variation were positioned on a RFLP-RAPD genetic map. Different DNA regions involved in constitutive and water stress responses were detected. In the stress treatment, one region on chromosome 1 was involved in RWC and NL variation giving a genetic basis to the phenotypic correlations found. Separated map positions were also found for RWC and NL. Epistatic interactions between several QTLs and between QTLs and other markers were detected only in the water stress treatment, suggesting that some chromosomal regions might be involved in the regulation of the expression of the traits under water stress. This work suggested that even if some parameters are strongly correlated, finding QTLs for only one trait is not sufficient to detect all the candidate regions which might be involved in the control of the correlated traits. The results of localization and co-localization of QTLs are physiologically interpreted.
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