Fungal infections of grapevine roots in phylloxera-infested vineyards

Wounds caused by feeding of grape phylloxera on grape roots can become infected with a variety of fungi. Fusarium roseum, F. oxysporum and Pythium ultimum are important in Vitis vinifera Chardonnay wounds whereas F. oxysporum and Cephalosporium sp. are important for the moderately tolerant rootstock AXR#1. Proportion of root lengths infected in the phloem parenchyma were measured in two vineyards through the 1996 growing season and into the winter. Infection rates were highest in spring (as measured in May) but decreased to a low level by the end of summer. There was a second infection peak in fall. We suggest that the decline in fungal infections was due to death of highly infected roots and their removal from the sampled pool of roots. Loss of roots is a logical cause of vine decline and explains why there have been poor correlations between phylloxera populations and vine damage symptoms

Population dynamics of grape phylloxera in California vineyards

Field monitoring was conducted to investigate population growth of grape phylloxera, Daktulosphaira vitifoliae (Fitch), in commercial grapevines in California. Phylloxera populations started from very low densities each spring, they increased exponentially and peaked during mid-summer, and then declined from mid-to late-summer. A second population peak was observed in the fall. Populations increased and declined simultaneously across all age classes. Egg populations were highest, followed by 1st and 2nd and then 3rd and 4th instars; adult populations were the lowest. The distribution of age classes as a proportion of the total population indicated a higher intrinsic rate of increase in field vines in spring and early summer than was observed in the laboratory. Densities of phylloxera on tuberosities were highest during the summer and coincided with the population maximum. Densities of phylloxera on nodosities were highest in early spring and in the fall and coincided with periods of root flush. Evaluation of the relationship of soil temperatures to developing phylloxera suggested that decline of phylloxera populations in mid-and late-summer cannot be attributed to temperatures below a developmental threshold. Decreased root quality or quantity and mortality factors may explain this decline. Phylloxera overwintered as 1st or 2nd instars. Analysis of spatial distribution of phylloxera using Taylor's power law and Iwao's patchiness regression indicated that phylloxera populations are aggregated. The significance of this research with respect to phylloxera management is discussed

Effects of fungal root infection on the vigor of grapevines infested by root-feeding grape phylloxera

The role of fungal pathogens in damage of grapevines (Vitis vinifera L.; cv. Chardonnay) associated with grape phylloxera (Daktulosphaira vitifoliae FITCH) was investigated. Seven different genera of secondary fungi were isolated from surface-disinfected feeding sites of phylloxera but none from surface-disinfected root tissues undamaged by phylloxera. Damage in vines infested with phylloxera and infected with Fusarium solani (MART.) or with F. solani and Pythium ultimum TROW. was significantly greater than damage in vines infested with phylloxera only. In a greenhouse experiment, total biomass was reduced by 16% in vines infested with phylloxera and 24 to 29% in vines infested with phylloxera and infected with fungus in comparison with control vines. Chlorophyll content, average internode length, shoot biomass, and root biomass in the uninfested, uninfected vines were significantly greater than vines infested with phylloxera or vines infested with phylloxera and infected with F. solani or P. ultimum, or both. Preventative treatment with metalaxyl, benomyl or copper quinolinolate fungicides significantly decreased damage in phylloxera-infested vines in comparison with untreated vines. The implications of this research with respect to management of grape phylloxera are discussed

Exploring the Time Domain With Synoptic Sky Surveys

Synoptic sky surveys are becoming the largest data generators in astronomy, and they are opening a new research frontier, that touches essentially every field of astronomy. Opening of the time domain to a systematic exploration will strengthen our understanding of a number of interesting known phenomena, and may lead to the discoveries of as yet unknown ones. We describe some lessons learned over the past decade, and offer some ideas that may guide strategic considerations in planning and execution of the future synoptic sky surveys.Comment: Invited talk, to appear in proc. IAU SYmp. 285, "New Horizons in Time Domain Astronomy", eds. E. Griffin et al., Cambridge Univ. Press (2012). Latex file, 6 pages, style files include

Improved correction of VIPERS angular selection effects in clustering measurements

AbstractClustering estimates in galaxy redshift surveys need to account and correct for the way targets are selected from the general population, as to avoid biasing the measured values of cosmological parameters. The VIMOS Public Extragalactic Redshift Survey (VIPERS) is no exception to this, involving slit collisions and masking effects. Pushed by the increasing precision of the measurements, e.g. of the growth rate f, we have been re-assessing these effects in detail. We present here an improved correction for the two-point correlation function, capable to recover the amplitude of the monopole of the two-point correlation function ξ(r) above 1 h-1 Mpc to better than 2

Augmenting photometric redshift estimates using spectroscopic nearest neighbours

As a consequence of galaxy clustering, close galaxies observed on the plane of the sky should be spatially correlated with a probability that is inversely proportional to their angular separation. In principle, this information can be used to improve photometric redshift estimates when spectroscopic redshifts are available for some of the neighbouring objects. Depending on the depth of the survey, however, this angular correlation is reduced by chance projections. In this work, we implement a deep-learning model to distinguish between apparent and real angular neighbours by solving a classification task. We adopted a graph neural network architecture to tie together photometry, spectroscopy, and the spatial information between neighbouring galaxies. We trained and validated the algorithm on the data of the VIPERS galaxy survey, for which photometric redshifts based on spectral energy distribution are also available. The model yields a confidence level for a pair of galaxies to be real angular neighbours, enabling us to disentangle chance superpositions in a probabilistic way. When objects for which no physical companion can be identified are excluded, all photometric redshift quality metrics improve significantly, confirming that their estimates were of lower quality. For our typical test configuration, the algorithm identifies a subset containing ~75% high-quality photometric redshifts, for which the dispersion is reduced by as much as 50% (from 0.08 to 0.04), while the fraction of outliers reduces from 3% to 0.8%. Moreover, we show that the spectroscopic redshift of the angular neighbour with the highest detection probability provides an excellent estimate of the redshift of the target galaxy, comparable to or even better than the corresponding template-fitting estimate.Comment: 9 pages, 12 figures, matching the accepted version. NezNet is available at https://github.com/tos-1/NezNe

Genetic Structure in Native Populations of Grape Phylloxera (Homoptera: Phylloxeridae)

Random amplified polymorphic DNA (RAPD) markers were used to study genetic structure and diversity in native grape phylloxera populations growing on Vitis arizonica Englemann in central Arizona and on V. riparia Michaux in New York. RAPD data from the Arizona collections were clustered into 3 subpopulations, whereas data from the New York collections were not clustered, which reflected topographic features and the distribution of the sampled vines. Similarity coefficients of the 2 collection areas had similar ranges (0.89-1.0). The similarity coefficient between the Arizona and New York collections was 0.62. Analyses of molecular variance were used to partition the variance in genetic distances, and confirmed the results of the dendrogram clustering. The clustering of the Arizona populations is likely the result of gene flow restriction caused by geographic isolation. Greater diversity was expected among the Arizona populations. That diversity levels were similar suggests that other factors, such as inbreeding or past population history, must play a role in the relatively low level of diversity found in Arizon

Average luminosity distance in inhomogeneous universes

The paper studies the correction to the distance modulus induced by inhomogeneities and averaged over all directions from a given observer. The inhomogeneities are modeled as mass-compensated voids in random or regular lattices within Swiss-cheese universes. Void radii below 300 Mpc are considered, which are supported by current redshift surveys and limited by the recently observed imprint such voids leave on CMB. The averaging over all directions, performed by numerical ray tracing, is non-perturbative and includes the supernovas inside the voids. Voids aligning along a certain direction produce a cumulative gravitational lensing correction that increases with their number. Such corrections are destroyed by the averaging over all directions, even in non-randomized simple cubic void lattices. At low redshifts, the average correction is not zero but decays with the peculiar velocities and redshift. Its upper bound is provided by the maximal average correction which assumes no random cancelations between different voids. It is described well by a linear perturbation formula and, for the voids considered, is 20% of the correction corresponding to the maximal peculiar velocity. The average correction calculated in random and simple cubic void lattices is severely damped below the predicted maximal one after a single void diameter. That is traced to cancellations between the corrections from the fronts and backs of different voids. All that implies that voids cannot imitate the effect of dark energy unless they have radii and peculiar velocities much larger than the currently observed. The results obtained allow one to readily predict the redshift above which the direction-averaged fluctuation in the Hubble diagram falls below a required precision and suggest a method to extract the background Hubble constant from low redshift data without the need to correct for peculiar velocities.Comment: 34 pages, 21 figures, matches the version accepted in JCA

Time Domain Explorations With Digital Sky Surveys

One of the new frontiers of astronomical research is the exploration of time variability on the sky at different wavelengths and flux levels. We have carried out a pilot project using DPOSS data to study strong variables and transients, and are now extending it to the new Palomar-QUEST synoptic sky survey. We report on our early findings and outline the methodology to be implemented in preparation for a real-time transient detection pipeline. In addition to large numbers of known types of highly variable sources (e.g., SNe, CVs, OVV QSOs, etc.), we expect to find numerous transients whose nature may be established by a rapid follow-up. Whereas we will make all detected variables publicly available through the web, we anticipate that email alerts would be issued in the real time for a subset of events deemed to be the most interesting. This real-time process entails many challenges, in an effort to maintain a high completeness while keeping the contamination low. We will utilize distributed Grid services developed by the GRIST project, and implement a variety of advanced statistical and machine learning techniques.Comment: 5 pages, 2 postscript figures, uses adassconf.sty. To be published in: "ADASS XIV (2004)", Eds. Patrick Shopbell, Matthew Britton and Rick Ebert, ASP Conference Serie

Attractancy of Racemic Disparlure and Certain Analogues to Male Gypsy Moths and the Effect of Trap Placement

Traps hung on small trees of 3-8 cm diam and baited with racemic epoxides, hydrocarbons and other analogues related to racemic cis-7,8-epoxy-2-methyloctadecane (disparlure) resulted in male Lymantria dispar L. (gypsy moth) catches statistically indistinguishable from those of unbaited traps. Only (±)-disparlure yielded trap catches statistically above the level of unbaited traps. However, trap placement on trees of ca. 0.5 m diam produced appreciable trap catches, even in unbaited trap