Spatial Distribution of Crown Gall in a Commercial Nursery of Weeping Fig

Abstract

Agrobacterium larrymoorei causes tumors on weeping fig. The association between propagation and pathogen spread in mother trees and daughter branches was studied in a commercial nursery. The mother tree planting was scouted for tumors prior to and after propagation. Branches selected for propagation were tagged to track disease development. The spatial distribution of crown gall in the mother tree planting was characterized with runs, join-count, and spatial autocorrelation analyses. The association of disease in mother trees and daughter branches was characterized with cross-correlation analysis. The incidence of crown gall in the mother tree planting increased from 7% prior to propagation to 32% eight months after propagation. Of the 4193 daughter branches monitored, 3.8% developed tumors. Runs analysis indicated significant clustering of diseased mother trees. Significant cross-correlations between mother trees and daughter branches with symptoms of crown gall were detected out to a distance of two plants from the source. Although pruning shears were routinely soaked in a disinfectant in this nursery, the degree of sterilization achieved apparently was not sufficient to prevent pathogen transmission. This study suggests that alternative sanitation measures should be sought and that infected mother trees and their neighbors should be avoided for propagation. Accepted for publication 5 November 2012. Published 26 November 2012.