Spatial variability of salt-affected soils in the middle Ebro Valley (Spain) and implications in plant breeding for increased productivity

Barley breeding programs have empirically selected for improving grain yield and quality. The objective of this study was to quantify genetic gains in yield in 2-rowed malting barley cultivars released from 1944to 1998 in Argentina, identifying the major physiological traits responsible for them. For this purpose, a field experiment was conducted in absence of biotic and abiotic stressful factors and with lodging being prevented mechanically. Until the 1970's,potential yield was maintained nearly constant at 5.25 mg ha^-1 and since then it increased at a rate of 41 kg ha^-1 year^-1. That bi-linear trend was closely related to the trend of averaged yields obtained by farmers. The contribution made by breeding yield potential to the total yield gains achieved by farmers was estimated in c. One third. Neither time to heading nor time to maturity were systematically modified by breeding. However, the partitioning of the developmental time was modified: time to achieve both maximum number of floret primordia and length of the jointing –heading period were increased with the year of release of the cultivars. The main component associated with yield was the number of grains per m², due to variations in number of spikes per m².Total and vegetative biomass at maturity increased with the year of release of the cultivars, at a rate of 45 and 19 kg ha^-1 year^-1, while both harvest index and stem height remained virtually unmodified. Differences in biomass at heading among cultivars were related to the improvement on the abilities to capture more radiation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic structure in Atlantic brown trout (Salmo trutta L.) populations in the Iberian peninsula: evidence from mitochondrial and nuclear DNA analysis

Brown trout (Salmo trutta L.) was sampled in rivers belonging to three different Spanish basins in order to analyse the distribution of genetic variability. The genetic analysis was performed by using two systems and techniques: nuclear DNA was screened through random amplified polymorphic DNAs (screening 2 × 10⁵ bp of the whole genome), and mitochondrial DNA (mtDNA) through sequencing of the hypervariable control region. Genetic distances between the populations were similar using either analysis although some differences arise. For example, some populations of the Tajo basin were very close through nuclear analysis but more distant using mtDNA. Differences between the two DNA sources could be the result of a different evolutionary rate, and the fact that mtDNA is maternally transmitted and differences in sex migration rates will influence the patterns of genetic variation between the transmitted DNAs. Total variation was partitioned using amova showing a clear subdivision among basins although intrapopulation variation remained as high as 62%. A correspondence analysis defined the differences in a three‐dimensional way, clustering the populations according to their common basin. When mtDNA was sequenced, higher variability was noted in the segment between 400 and 600 bp of the whole D‐loop sequence, suggesting that these 200 bp improved the analysis of the variability more than sequencing the t‐RNA ends of the control region. A comparison was made between the t‐RNA^Pro ends of the 10 populations screened here and the rest of the published sequences found in the literature, leading to a concentration of these populations in group IV which includes all trouts which originate in the Atlantic. The analyses performed suggest that a high genetic variability is present in all populations and that although there has been a probable interference from stocked strains introduced to increase population density, this was only detectable through the variance between rivers which reflect different policies according to the region where the basin is located. However, the genetic analysis using the two approaches allows the control of the natural populations avoiding a loss of their genetic potential.