A comparative assessment of potential components of partial disease resistance to Fusarium head blight detected in a detached leaf assay of wheat, barley and oats.

The relative resistance of 15 winter barley, three winter wheat and three winter oat cultivars on the UK recommended list 2003 and two spring wheat cultivars on the Irish 2003 recommended list were evaluated using Microdochium nivale in detached leaf assays to further understand components of partial disease resistance (PDR) and Fusarium head blight (FHB) resistance across cereal species. Barley cultivars showed incubation periods comparable to, and latent periods longer than the most FHB resistant Irish and UK wheat cultivars evaluated. In addition, lesions on barley differed from those on wheat as they were not visibly chlorotic when placed over a light box until sporulation occurred, in contrast to wheat cultivars where chlorosis of the infected area occurred when lesions first developed. The pattern of delayed chlorosis of the infected leaf tissue and longer latent periods indicate that resistances are expressed in barley after the incubation period is observed, and that these temporarily arrest the development of mycelium and sporulation. Incubation periods were longer for oats compared to barley or wheat cultivars. However, oat cultivars differed from both wheat and barley in that mycelial growth was observed before obvious tissue damage was detected under macroscopic examination, indicating tolerance of infection rather than inhibition of pathogen development, and morphology of sporodochia differed, appearing less well developed and being much less abundant. Longer latent periods have previously been related to greater FHB resistance in wheat. The present results suggest the longer latent periods of barley and oat cultivars, than wheat, are likely to play a role in overall FHB resistance if under the same genetic control as PDR components expressed in the head. However the limited range of incubation and latent periods observed within barley and oat cultivars evaluated was in contrast with wheat where incubation and latent periods were shorter and more variable among genotypes. The significance of the various combinations of PDR components detected in the detached leaf assay as components of FHB resistance in each crop requires further investigation, particularly with regard to the apparent tolerance of infection in oats and necrosis in barley, after the incubation period is observed, associated with retardation of mycelial growth and sporulation.

Components of resistance to Fusarium head blight in wheat detected in a seed germination assay with Microdochium majus and the relationship to FHB disease development and mycotoxin accumulation from Fusarium graminearum infection.

Components of partial disease resistance (PDR) to fusarium head blight (FHB), detected in a seed-germination assay, were compared with whole-plant FHB resistance of 30 USA soft red winter wheat entries in the 2002 Uniform Southern FHB Nursery. Highly significant (P <0·001) differences between cultivars in the in vitro seed-germination assay inoculated with Microdochium majus were correlated to FHB disease incidence (r = -0·41; P <0·05), severity (r = -0·47; P <0·01), FHB index (r = -0·46; P <0·01), damaged kernels (r = -0·52; P <0·01), grain deoxynivalenol (DON) concentration (r = -0·40; P <0·05) and incidence/severity/kernel-damage index (ISK) (r = -0·45; P <0·01) caused by Fusarium graminearum. Multiple linear regression analysis explained a greater percentage of variation in FHB resistance using the seed-germination assay and the previously reported detached-leaf assay PDR components as explanatory factors. Shorter incubation periods, longer latent periods, shorter lesion lengths in the detached-leaf assay and higher germination rates in the seed-germination assay were related to greater FHB resistance across all disease variables, collectively explaining 62% of variation for incidence, 49% for severity, 56% for F. graminearum-damaged kernels (FDK), 39% for DON and 59% for ISK index. Incubation period was most strongly related to disease incidence and the early stages of infection, while resistance detected in the seed germination assay and latent period were more strongly related to FHB disease severity. Resistance detected using the seed-germination assay was notable as it related to greater decline in the level of FDK and a smaller reduction in DON than would have been expected from the reduction in FHB disease assessed by visual symptoms.

DFT and in situ EXAFS investigation of gold/ceria-zirconia low-temperature water gas shift catalysts: Identification of the nature of the active form of gold

A combined experimental and theoretical investigation of the nature of the active form of gold in oxide-supported gold catalysts for the water gas shift reaction has been performed. In situ extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) experiments have shown that in the fresh catalysts the gold is in the form of highly dispersed gold ions. However, under water gas shift reaction conditions, even at temperatures as low as 100 degrees C, the evidence from EXAFS and XANES is only 14 consistent with rapid, and essentially complete, reduction of the gold to form metallic clusters containing about 50 atoms. The presence of Au-Ce distances in the EXAFS spectra, and the fact that about 15% of the gold atoms can be reoxidized after exposure to air at 150 degrees C, is indicative of a close interaction between a fraction (ca. 15%) of the gold atoms and the oxide support. Density functional theory (DFT) calculations are entirely consistent with this model and suggest that an important aspect of the active and stable form of gold under water gas shift reaction conditions is the location of a partially oxidized gold (Audelta+) species at a cerium cation vacancy in the surface of the oxide support. It is found that even with a low loading gold catalysts (0.2%) the fraction of ionic gold under water gas shift conditions is below the limit of detection by XANES (<5%). It is concluded that under water gas shift reaction conditions the active form of gold comprises small metallic gold clusters in intimate contact with the oxide support.

Do pigs form preferential associations?

This investigation examined whether pigs form long-term preferential associations or ‘friendships’ and factors that may influence the formation of these relationships. Thirty-three pigs from 16 litters were housed together from 4 weeks of age. At 10 weeks they were split into two groups of 16 and 17 pigs and each introduced into 3.05 m × 3.66 m observation pens (1st pen). At 17 weeks the two groups swapped pens (2nd pen). The lying patterns of each group were recorded over 3 weeks in both the 1st and 2nd pens. To identify dyads with preferential associations, association indices were calculated for each pair based on their lying patterns and analysed using SOCPROG1.3 and the permutation method [Whitehead, H., 1999. Programs for analysing social structure. SOCPROG 1.2, http://is.dal.cal/~whitelab/index.htm]. Dyads with high association indices for at least 2 out of 3 weeks in either pen, i.e. =0.10 (twice the mean), were classed as having preferential associations. Mantel tests were used to examine the relationship between the relative sex, weight, familiarity and relatedness of a dyad and their level of association and to examine consistency of associations between pens. The existence of preferential associations was identified in both groups, since the standard deviations for the observed half-weight association index means were significantly higher than for the randomly permuted half-weight association index means (P < 0.001). Of the 33 pigs observed, 32 formed preferential associations with one or more pigs in their group, resulting in 50 dyads. Only six dyads (12 pigs) formed preferential associations in both pens, suggesting that the remaining dyads either formed short-term associations only or were simply displaying a shared preference for the same lying location. Levels of association between pens showed no significant correlation. The relative sex, weight, familiarity and relatedness of dyad members also showed no significant correlation with their level of association. These findings suggest that unrelated pigs are capable of forming preferential associations. However, it is unclear whether such associations are widespread or important to pigs, since most dyads’ preferential associations were not consistent between pens.