Laurel wilt, caused by Raffaelea lauricola, threatens native and non-native species in the Lauraceae in the south-eastern USA. Avocado, Persea americana, is the most important agricultural suscept of laurel wilt. Grafted plants (clonal scions on seedling rootstocks) of 24 cultivars were screened against the disease in the field from 2008 to 2010. Disease was induced with either mycelial plugs or conidial suspensions of R. lauricola. There were significant differences in the severity of disease that developed on different cultivars, and West Indian cultivars were most susceptible (P < 0AE05). Simmonds, a West Indian cultivar that comprises 35% of the commercial production in Florida, was consistently susceptible and was used as a standard genotype in different studies. Disease severity increased significantly on cv. Simmonds as plant size (stem diameter) increased (P < 0AE0042). In greenhouse studies, internal (sapwood) and external disease severities on cv. Simmonds were correlated (P < 0AE0001), and a threshold was evident, in that external symptoms developed only after moderately severe symptoms had developed internally. Latent infection was uncommon; R. lauricola was usually isolated on a semiselective medium or detected via qPCR only from discoloured xylem of inoculated cv. Simmonds. As basipetal movement of the pathogen was common, its movement among trees via root grafts is probable. Greater understanding is needed of the movement of R. lauricola in naturally and artificially infected trees, and whether sufficient tolerance exists in avocado to assist in the management of this important new disease.
Ploetz, R. C, Pérez-Martínez, J. M., Evans, E. A., and Inch, S. A. 2011. Toward fungicidal management of laurel wilt of avocado. Plant Dis. 95:977-982.Laurel wilt threatens commercial and residential production of avocado (Persea americana) in Florida. Laurel wilt on redbay (P. borbonia) was controlled previously with macroinfusions (injections) of Alamo, an injectable formulation of propiconazole. To detennine whether Alamo macroinfusion would be cost effective in commercial avocado production, economic analyses were conducted for various macroinfusion scenarios and a standardized production situation in southern Florida. Under prevailing conditions, macroinfusion was not cost effective. In the interest of identifying alternative means to manage the disease, other fungicides and application measures were evaluated. In all, 20 fungicides in 15 chemical groups and 10 fungicide groups were examined in vitro. In vitro inhibition of the radial growth of the pathogen Raffaelea lauricola was determined on fungicide-amended malt extract agar; demethylation inhibitors (DMIs; fenarimol, myclobutanil, propiconazole, prothioconazole, triadimenol, triadimefon, and triticonazole), quinone outside inhibitors (azoxystrobin, pyraclostrobin, and fluoxastrobin), and a quinone inside inhibitor (fluazinam) had the greatest impact on radial growth (the concentration at which growth was reduced by 50% was >0.1 (Jg ml"'). In greenhouse studies, the most in-hibitory products in vitro, plus thiabendazole and two products that were not tested in vitro, flutriafol and a potassium salts mixture of phosphorus acid, were tested for disease suppression on anificially inoculated, potted 'Simmonds,' a susceptible avocado cultivar. In general, soil drench applications of the above DMIs and thiabendazole but not azoxystrobin, pyraclostrobin, fluazinam, or the phosphorus acid salt provided significant control of disease (P < 0.05). Topical branch or trunk applications of propiconazole, and triadimenol in 2% Pentrabark, a bark-penetrating surfactant, were also effective at lower rates than were used in drench applications. Comparable levels of disease suppression were achieved when propiconazole was applied at 11 % of the rates that were used in soil drenches. Although topical fungicide applications in bark-penetrating surfactants would be a less expensive practice than macroinfusion, moving sufficient concentrations of propiconazole or other fungicides into host xylem will be difficult in trees that are larger than the potted plants that were tested in these trials. Ongoing work examines means by which this goal might be met on fruit-bearing trees in the field.
We report a detailed CO(1−0) survey of a galaxy protocluster field at z = 2.16, based on 475 h of observations with the Australia Telescope Compact Array. We constructed a large mosaic of 13 individual pointings, covering an area of 21 arcmin2 and ±6500 km s−1 range in velocity. We obtained a robust sample of 46 CO(1−0) detections spanning z = 2.09 − 2.22, constituting the largest sample of molecular gas measurements in protoclusters to date. The CO emitters show an overdensity at z = 2.12 − 2.21, suggesting a galaxy super-protocluster or a protocluster connected to large-scale filaments of ∼120 cMpc in size. We find that 90% of CO emitters have distances >0.′5−4′ to the center galaxy, indicating that small area surveys would miss the majority of gas reservoirs in similar structures. Half of the CO emitters have velocities larger than escape velocities, which appears gravitationally unbound to the cluster core. These unbound sources are barely found within the R200 radius around the center, which is consistent with a picture in which the cluster core is collapsed while outer regions are still in formation. Compared to other protoclusters, this structure contains a relatively higher number of CO emitters with relatively narrow line widths and high luminosities, indicating galaxy mergers. We used these CO emitters to place the first constraint on the CO luminosity function and molecular gas density in an overdense environment. The amplitude of the CO luminosity function is 1.6 ± 0.5 orders of magnitude higher than that observed for field galaxy samples at z ∼ 2, and one order of magnitude higher than predictions for galaxy protoclusters from semi-analytical SHARK models. We derive a high molecular gas density of 0.6 − 1.3 × 109 M⊙ cMpc−3 for this structure, which is consistent with predictions for cold gas density of massive structures from hydro-dynamical DIANOGA simulations.
Aims. The relationship between baryonic and dark components in galaxies varies with the environment and cosmic time. Galaxy scaling relations describe strong trends between important physical properties. A very important quantitative tool in case of spiral galaxies is the Tully-Fisher relation (TFR), which combines the luminosity of the stellar population with the characteristic rotational velocity (V max ) taken as proxy for the total mass. In order to constrain galaxy evolution in clusters, we need measurements of the kinematic status of cluster galaxies at the starting point of the hierarchical assembly of clusters and the epoch when cosmic star formation peaks. Methods. We took spatially resolved slit FORS2 spectra of 19 cluster galaxies at z ∼ 1.4, and 8 additional field galaxies at 1 < z < 1.2 using the ESO Very Large Telescope. The targets were selected from previous spectroscopic and photometric campaigns as [OII] and H α emitters. Our spectroscopy was complemented with HST/ACS imaging in the F775W and F850LP filters, which is mandatory to derive the galaxy structural parameters accurately. We analyzed the ionized gas kinematics by extracting rotation curves from the two-dimensional spectra. Taking into account all geometrical, observational, and instrumental effects, we used these rotation curves to derive the intrinsic maximum rotation velocity. Results. V max was robustly determined for six cluster galaxies and three field galaxies. Galaxies with sky contamination or insufficient spatial rotation curve extent were not included in our analysis. We compared our sample to the local B-band TFR and the local velocitysize relation (VSR), finding that cluster galaxies are on average 1.6 magnitudes brighter and a factor 2-3 smaller. We tentatively divided our cluster galaxies by total mass (i.e., V max ) to investigate a possible mass dependency in the environmental evolution of galaxies. The averaged deviation from the local TFR is ∆M B = −0.7 for the high-mass subsample (V max > 200 km/s). This mild evolution may be driven by younger stellar populations (SP) of distant galaxies with respect to their local counterparts, and thus, an increasing luminosity is expected toward higher redshifts. However, the low-mass subsample (V max < 200 km/s) is made of highly overluminous galaxies that show ∆M B = −2.4 mag. When we repeated a similar analysis with the stellar mass TFR, we did not find significant offsets in our subsamples with respect to recent results at similar redshift. While the B-band TFR is sensitive to recent episodes of star formation, the stellar mass TFR tracks the overall evolution of the underlying stellar population. In order to understand the discrepancies between these two incarnations of the TFR, the reported B-band offsets can no longer be explained only by the gradual evolution of stellar populations with lookback time. We suspect that we instead see compact galaxies whose star formation was enhanced during their infall toward the dense regions of the cluster through interactions with the int...
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