Evaluation of fungicide seed treatments for control of seedborne neck rot fungi of onion, 2007

摘要

A seed lot of a proprietary onion cultivar naturally infected with neck rot Botrytis spp. (B. aclada and B. allii) was used to evaluate fungicide seed treatments for control of seedborne Botrytis spp. For the Coronet, Rovral 4F, and Thiram 42-S treatments, seeds were placed in a slurry of a proprietary blue liquid colorant (3.5% by seed weight mixed 1:1 with water), to which the appropriate fungicide was added. Seeds were treated with water + colorant for the control treatment. The seeds and slurry were shaken in a flask until the slurry was adsorbed completely onto the seeds. Other seed treatments were done by the registrants, i.e., AgriCoat LLC (Soledad, CA) for the organic actinomycete product Natural II, and Syngenta Crop Protection (Stanton, MN) for the FarMore D300 treatments. Seed germination was tested for four replications of 100 seeds/treatment using the blotter assay protocol of the Association of Official Seed Analysts (AOSA). A seed health assay was also completed for four replicationsof 100 seeds/treatment by plating seeds onto Kritzman and Netzer’s semi-selective agar medium in Petri dishes (20 seeds/plate, 5 plates/replication). The dishes were sealed with Parafilm and incubated at 22oC with near-UV and fluorescent light on a 12h/12 h dayight cycle for 14 d. Seeds were examined microscopically after 5, 9, and 14 d. For each of four replications of a grow-out assay, one flat consisting of 200 cells (each cell 4.0 cm2 x 3.5 cm deep) was planted with seed from each treatment (1seed/cell into Redi-Earth Peat-Lite planting mix). The flats were placed in a greenhouse (23 +- 2oC) on a 12 h/12 h dayight schedule. A micro-sprinkler system applied a fine spray of water over the flats for 1 min every 30 min to promote humid conditions conducive for seed transmission of Botrytis spp. Emergence was counted 6, 8, 10, 12, 14, 16, and 24 d after planting. The flats of two replications were then placed at 5 +- 2oC for 5 d. The basal plate and roots were cut off each seedling, and the remainder of each seedling placed in a moist chamber for 7 d. The seedlings were then examined for Botrytis spp. The other two replications of seedlings were processed a week later.