New molecular markers linked to qualitative and quantitative powdery mildew and scald resistance genes in barley for dry areas

A partial genetic linkage map was constructed on 71 doubled-haploid lines derived from a cross between the barley lines Tadmor and WI2291 with 181 molecular markers. The segregating population was used to detect markers linked to the gene Mlg conferring resistance to powdery mildew (Erysiphe graminis f. sp. hordei) and to genes for quantitative resistance to scald (Rhynchosporium secalis). The gene Mlg on chromosome 4H was flanked by two AFLP markers at a distance of 2.0 and 2.4 cM, respectively. QTLs for resistance to scald were detected on chromosomes 2H and 3H. This association of molecular markers with qualitative and quantitative disease resistance loci represents a valuable starting-point for marker-assisted selection. This revised version was published online in July 2006 with corrections to the Cover Date.     

Segregation distortion in doubled haploid lines of barley (Hordeum vulgare L.) detected by simple sequence repeat (SSR) markers

A total of 147 simple sequence repeat (SSR) markers (including86 barley and 61 wheat microsatellite markers) were tested for their segregation in a doubled haploid (DH) and an F₂ population of barley. The DH population consisted of 71 doubled haploid lines, developed from F₁ plants of a cross between Tadmor and WI2291using isolated microspore culture technique. A genetic linkage map consisting of 43 microsatellite markers was constructed using the DH population. Particularly on chromosome 4H microsatellite markers showed distorted segregation ratios. Segregation of DH lines based on molecular markers were compared with segregation of 92 F₂ lines from the same cross. The proportion of loci deviating from the expected monogenic segregation ratios in the DH population was significantly higher (19/43loci, 44%) than in the F₂ population (7/43 loci, 16%). The deviation was biased towards the WI2291 parent alleles. In line with this observation, WI2291 was found to perform better than Tadmor in regenerating green plantlets with the isolated microspore-culture technique. This revised version was published online in July 2006 with corrections to the Cover Date.     

Weed management and irrigation are key treatments in emerging black truffle (Tuber melanosporum) cultivation

Interest in conversion of marginal agricultural lands to small oak woodlands for the production of black truffles (Tuber melanosporum Vittad.) is increasing in the native black truffle areas of France, Spain and Italy as well as suitable or amended sites throughout the world due to high economic returns for gastronomically valuable truffles. Successful long-term management of a perennial plantation replacing an annual crop requires understanding the system in all phases of the life cycle, and in the case of truffles this involves understanding the interactive growth of the aboveground host and the belowground symbiotic ectomycorrhizal fungus whose fruitbody is the desired truffle. Here we focus on the pre-production phase, 4 years after establishing the truffle-oak plantation and prior to truffle production. We tested the influence of weed control, irrigation and fertilizer, each at 3 levels, on plant growth and ectomycorrhizal proliferation in three truffle-oaks plantations in northeast Spain. Results show that adequate weed control improves root and shoot dry weight while fertilizer and irrigation treatments did not influence plant growth. The low dose of irrigation (50% of the estimated water deficit for the site) and glyphosate weed control both increased total root tips/plant and T. melanosporum colonized tips (ectomycorrhizae) by approximately two-fold, compared to control treatments. Distribution of the ectomycorrhizae within the soil profile was significantly influenced by the low dose irrigation treatment, with increases observed in the 10?C20 cm and the 20?C30 cm deep layers compared to the control and high irrigation treatments. Four years after planting, T. melanosporum remained the dominant fungal symbiont, despite the presence of 14 other ectomycorrhizal morphotypes from these sites.     

Reference evapotranspiration estimation without local climatic data

The Penman–Monteith equation for reference evapotranspiration (ET_o) estimation cannot be applied in many situations, because climatic records are totally or partially not available or reliable. In these cases, empirical equations that rely on few climatic variables are necessary. Nevertheless, the uncertainty associated with empirical model estimations is often high. Thus, the improvement of methods relying on few climatic inputs as well as the development of emergency estimation tools that demand no local climatic records turns into a task of great relevance. The present study describes different approaches based on multiple linear regression, simple regression and artificial neural networks (ANNs) to deal with ET_o estimation exclusively from exogenous records from secondary stations. This cross-station approach is based on a continental characterization of the study region, which enables the selection and hierarchization of the most suitable ancillary data supplier stations. This procedure is compared with different traditional and cross-station approaches, including methodologies that also consider local temperature inputs. The proposed methods are also evaluated as gap infilling procedures and compared with a simple methodology, the window averaging. The artificial neural network and the multiple linear regression approaches present very similar performance accuracies, considerably higher than simple regression and traditional temperature-based approaches. The proposed input combinations allow similar performance accuracies as ANN models relying on exogenous ET_o records and local temperature measurements. The cross-station multiple linear regression procedure is recommended due to its higher simplicity.     

Establishing maximum daily trunk shrinkage and midday stem water potential reference equations for irrigation scheduling of early maturing peach trees

Measurements of midday stem water potential (Ψ_stem) and maximum daily trunk shrinkage (MDS) were taken over a 4-year period in early maturing peach trees (Prunus persica (L.) Batsch cv. Flordastar) grafted on GF-677 rootstock. Plants were irrigated daily above their water requirements in order to obtain non-limiting soil water conditions. The results indicated that seasonal reference equations can be obtained for MDS and Ψ_stem using crop reference evapotranspiration (ETo), daily mean vapour pressure deficit (VPD_m) and mean daily air temperature (T_m) in the case of MDS, and ETo and VPD_m in the case of Ψ_stem. In this way, VPD_m was seen to be the best predictor of MDS and Ψ_stem, without both were influenced significantly by yield or crop load variations between years. When the postharvest regression between MDS or Ψ_stem and the meteorological parameters mentioned were broken down into early and late postharvest periods, the correlation coefficients improved and were closely related to the presence or absence of sugar-demanding sinks, such as active root growth. A negative linear relationship between MDS and Ψ_stem was found, pointing to unchanging radial hydraulic conductivity in the bark tissues and suggesting that MDS depends to a great extent of the water potential.     

Tree regeneration and plant species diversity responses to vegetation control following a major windthrow in mixed broadleaved stands

By increasing resource availability, canopy opening enhances tree recruitment as well as the development of neighbouring vegetation. The proliferation of early successional and highly competitive vegetation may have dramatic consequences on seedling establishment. However, differences in competitive abilities have been shown among the plant growth forms commonly encountered in forests. We may thus expect that vegetation management leading to control of different plant growth forms would have different consequences on tree seedling growth and development. To test this hypothesis, we analysed the effects of an intensity gradient of four vegetation control treatments (untreated, coppice control, coppice and non-tree plant control, and coppice, non-tree and pioneer (tree) plant control) on plant species richness and natural tree regeneration in three post-storm sites. Higher plant species richness and a better natural tree regeneration were observed in the more intensive treatments that significantly improved the balance of the relative abundance of tree species. Suppressing the more competitive vegetation, mainly Rubus fruticosus and graminoids, led to the recruitment and growth of tree species sensitive to competition and good tree species diversity. Practical recommendations in terms of vegetation control relative to tree regeneration and plant species richness are given.     

Does tree seedling growth and survival require weeding of Himalayan balsam (Impatiens glandulifera)?

The effect of Himalayan balsam (Impatiens glandulifera) on survival and growth of naturally regenerated silver birch (Betula pendula) and planted Norway spruce (Picea abies) and silver fir (Abies alba) seedlings was studied in a weeding experiment over 3 years. Three different treatments were applied: control, mowing, and hand weeding by pulling out the entire plant. There were no consistent treatment effects on height and diameter of the tree seedlings. The coverage of Rubus fruticosus had a negative impact on diameter increment of Norway spruce and silver fir. As opposed to growth, treatment effects on seedling survival could be found for planted Norway spruce and silver fir. However, it is very likely that these effects, namely higher seedling survival after mowing, have to be attributed to the control of bramble (Rubus fruticosus) rather than to that of Himalayan balsam. It is concluded that Himalayan balsam is not able to seriously affect the growth of already established seedlings.     

Cone beam computed tomography and intraoral radiography for diagnosis of dental abnormalities in dogs and cats

The development of veterinary dentistry has substantially improved the ability to diagnose canine and feline dental abnormalities. Consequently, examinations previously performed only on humans are now available for small animals, thus improving the diagnostic quality. This has increased the need for technical qualification of veterinary professionals and increased technological investments. This study evaluated the use of cone beam computed tomography and intraoral radiography as complementary exams for diagnosing dental abnormalities in dogs and cats. Cone beam computed tomography was provided faster image acquisition with high image quality, was associated with low ionizing radiation levels, enabled image editing, and reduced the exam duration. Our results showed that radiography was an effective method for dental radiographic examination with low cost and fast execution times, and can be performed during surgical procedures.