ARS | Publication request: Investigations of Crown Gall in the Commercial Propagation of Weeping Fig

Submitted to: American Phytopathological Society
Publication Type: Abstract Only
Publication Acceptance Date: May 21, 2010
Publication Date: August 9, 2010
Citation: Turechek, W. 2010. Investigations of Crown Gall in the Commercial Propagation of Weeping Fig. American Phytopathological Society.

Interpretive Summary: Agrobacterium larrymoorei causes galls on the trunk, branches, and stems of weeping fig (Ficus benjamina L.). The extent to which this pathogen is transmitted through cuttings and the extent to which it is spread through the mother planting as a result of preparing air layers and subsequently pruning them to produce braided plants were studied in a commercial nursery. Branches selected for propagation were chosen from mother trees with no visible signs of galls and tagged for future tracking. Rooted branches were cut from the mother tree, braided with 2 to 4 other branches, planted in pots, and then placed on ground cloth to establish. Gall formation was tracked on all branches of each braided plant. Additional ratings were taken in the mother tree planting 6 months after pruning. In the mother tree planting, there was significant spatial correlation between mother trees infected before pruning and trees infected after pruning. There were also significant correlations between infected mother trees and braided plants established with 1 or more branches propagated from infected mother trees. There did not appear to be any correlation between the time of year when plants were propagated and gall formation. Although pruning shears are routinely soaked in sterilization medium in commercial practice, the degree of sterilization achieved in this nursery was not sufficient for reducing disease spread.

Technical Abstract: Whitefly-transmitted Squash vein yellowing virus (SqVYV) and Cucurbit leaf crumple virus (CuLCrV), and aphid-transmitted Papaya ringspot virus type W (PRSV-W) have had serious impact on watermelon production in southwest and west-central Florida in recent years. Tissue blot nucleic acid hybridization assays were developed for simple, high throughput detection of these three viruses as well as the more recently introduced Cucurbit yellow stunting disorder virus (CYSDV). To determine virus distribution within plants, we collected 80 entire plants randomly, 20 each on four different dates, from a commercial watermelon field showing symptoms of SqVYV, CuLCrV and PRSV-W, and possibly CYSDV. This was followed by a smaller sampling of five plants in a different commercial planting. Tissue prints were made from cross sections of watermelon plants from the crowns through the tips at 0.6 m intervals on nylon membranes and nucleic acid hybridization assays were used for virus detection. Results from testing of crown tissue showed that SqVYV, CuLCrV and PRSV-W were present in approximately 37%, 43.5% and 54%, respectively, of the 80 plants from the first field. For individual vines diagnosed with SqVYV, the distribution of SqVYV in vine tissue decreased proportionately with distance from the crown. The probability of detecting SqVYV was 70% at the base of the vine, compared to 23% at the tip of the vine, In contrast, CuLCrV tended to be more evenly distributed throughout the plant with a slightly higher probability of detection at the growing tip. The distribution of PRSV-W resembled that of SqVYV, but with a slightly greater probability of detection at the tip of the vine. Similar trends were detected in the smaller sampling; however, CYSDV was also detected in these plants. Overall, our results indicate that SqVYV, CuLCrV, and PRSV-W are distributed differently in watermelon plants, and this difference has implications for sample collection, and may affect vector acquisition and transmission of these viruses.