Analysis of the Spatial Spread of Sharka (Plum Pox Virus) in Apricot and Peach Orchards in Eastern Spain

Abstract

Spatial patterns of sharka disease, caused by plum pox virus (PPV) and vectored by several species of aphid, were determined by double antibody sandwich-enzyme-linked immunosorbent assay using polyclonal antibodies in newly infected, mature apricot and peach orchards in eastern Spain. Among yearly assessments of plots examined for within-and across-row aggregation of adjacent sharka-diseased trees, only a few transects were found to have aggregation by ordinary runs analyses. Analyses, using beta-binomial index of dispersion ( 14) to determine if spatial aggregation was present in each plot for data partitioned into quadrats of different spatial dimension, demonstrated occasional aggregation and results were generally inconclusive. Significant (1;) values, when present, were generally found associated with plots with higher disease incidence. No disease gradients were discernible for any of the plots and years. More rigorous spatial analyses were used to test for spatial relationships over longer distances. Twodimensional distance class analyses indicated a spatial dependency of PPV-infected stone-fruit trees over distance, a general scarcity of significant distance classes near the origin, and the presence of significant distance classes occasionally comprising small loose clusters at distances near the center or distal end of the proximity matrices especially during the initial stages of the epidemics. Geostatistical analysis confirmed the lack of significant associations among immediately adjacent trees and the trend for higher order spatial associations in semivariograms for distances corresponding to the center and distal ends of the proximity matrices. This trend in semivariance over distance was best described by linear or exponential increase models compared with transitional models commonly used in geostatistics. Correlation analysis indicated a significant conservation of orientation of localized systemic infections in scaffold branches over years. The spatial patterns of sharka suggest the lack of movement of PPV-viruliferous aphid vectors to immediately adjacent trees and their preferential movement to trees several tree spaces away.

Spread and competitiveness of Plum Pox Virus: Rec and ‐D strains in experimental plum orchard

“…() found a wide range of spatial patterns of PPV‐M spread in peach orchards in France, ranging from no aggregation to high aggregation of symptomatic trees, depending on diseases incidence and some other factors. Lack of adjacent, tree‐to‐tree spread of PPV and the presence of loose cluster of infected trees at further distances in apricot orchards was connected with the behaviour of aphid vectors (Gottwald, Avinent, Llacer, Hermoso de Mendoza, & Cambra, ). In our experiment, the slight decrease of infected trees from north to south (22 versus 16), and from west to east (20 versus 18) borders of the orchard indicated a possible influence of the distance from infected P. cersifera (all located at West) and plum trees (North—private orchard).…”

How does winter pruning affect peach tree–Myzus persicae interactions?

“…Our results did not support the hypothesis that peach trees need to be totally protected from aphids if they are not involved in sharka epidemic. However, resident aphids such as M. persicae should be less involved in the spread of the sharka disease than migratory aphid species (Gottwald et al., 1995). Results highlight the relevance of studying winter pruning as a potential complementary method of aphid control in orchards, given the relative capacity of peach trees to tolerate a certain level of aphids without major production losses, as was demonstrated in this study, thus confirming results of Leclant & Remaudière (1970).…”

Plum pox virus strains: Diversity and geographical distribution in Serbia

“…the specific reaction of any given isolate, host or aphid species. PPV-D isolates may also induce epidemics in peach, apricot and plum (Gottwald et al, 1995;Dallot et al, 1998;Polák & Komínek, 2009). …”