Spatial and Temporal Pattern Analyses of Esca Grapevine Disease in Vineyards in France.

To assess the capacity of esca to spread within vineyards of the Bordeaux region, over 8 years of annual records, containing between 1,200 and 2,300 contiguous Cabernet Sauvignon vines from 15 mature vineyards, were used for spatial statistical analyses. A group of nonparametric tests, based on join count statistics and on permutation methods, was developed to characterize the spatial structure of esca-symptomatic vines in terms of spread in any direction or within-row only. Among vineyards, a large range of spatial patterns, from random to strongly structured, associated with various prevalence rates that increased over time were observed. In four vineyards, the complex esca distribution pattern indicated different levels of clustering. By contrast, in other vineyards, only small clusters of two adjacent symptomatic vines were observed, and they were localized along rows, without enlargement over time, except in one vineyard. An analysis of spatial dependence between previously and newly symptomatic vines within k-order neighborhoods (k = 1 to 5), showed, for 5 of the 15 vineyards, that the newly symptomatic vines were located close to previously infected vines, without a favored orientation or neighbor order. All the results together suggested a limited potential for secondary local spread from neighboring symptomatic vines.

Influence of Pythium oligandrum on the bacterial communities that colonize the nutrient solutions and the rhizosphere of tomato plants.

The influence exerted by the biocontrol oomycete Pythium oligandrum on the bacterial populations proliferating in the rhizosphere of tomato plants grown in a hydroponic system and in the circulating solutions is studied in the present experiment. Quantitative PCR and single-strand conformation polymorphism were used to investigate the genetic structure and dynamics of the bacterial communities colonizing the root systems and the various circulating solutions. Quantitative PCR assays showed that bacteria heavily colonized the rhizosphere of tomato plants with, however, no significant density changes throughout the cultural season (April-September). Single strand conformation polymorphism fingerprints revealed the occurrence of transient perturbations in the rhizospheric indigenous bacterial communities following P. oligandrum introduction in the root system of plants. This effect was, however, transient and did not persist until the end of the cropping season. Interestingly, the genetic structure of the bacterial microflora colonizing either the roots or the nutrient solutions evolved throughout the cropping season. This temporal evolution occurred whatever the presence and persistence of P. oligandrum in the rhizosphere. Evidence is also provided that bacterial microflora that colonize the root system are different from the ones colonizing the circulating solutions. The relationships between these 2 microflora (at the root and solution levels) are discussed.