Seedlot characteristics. To determine the percentage of A. citrulli-infested seeds infestation for each lot, four samples (n = 100 seeds/lot) were planted on blotter paper (Anchor Paper Co., St. Paul, MN) saturated with sterile water in transparent plastic boxes [6 cm (H) ×24 cm (W) × 33.5 cm (L); Tri-State Plastics, Dixon, KY, USA] and
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maintained at 30°C and 85% RH with continuous fluorescent light for 14 days. Seeds from the fruits of blossoms that were pistil-inoculated with PBS were used as negative controls. Seed germination percentages and BFB seedling transmission percentages ((number of seedlings with BFB symptoms divided by the total number of seeds germinated) × 100) were recorded at 14 days after planting (DAP). Additionally, mean A. citrulli CFU/seed for samples (n = 30 seeds) from each lot were determined by ten-fold serial dilution of individually macerated seeds followed by spread-plating onto Nunhem’s semi-selective agar (Nunhems Seed Company, Haelen, The Netherlands). After incubation for 5 - 6 days at 28oC, A. citrulli colonies were enumerated and mean CFU/seed was determined for each lot.
Seedlot characteristics. To determine the percentage of A. citrulli-infested seeds infestation for each lot, four samples (n = 100 seeds/lot) were planted on blotter paper (Anchor Paper Co., St. Paul, MN) saturated with sterile water in transparent plastic boxes [6 cm (H) ×24 cm (W) × 33.5 cm (L); Tri-State Plastics, Dixon, KY, USA] and33maintained at 30°C and 85% RH with continuous fluorescent light for 14 days. Seeds from the fruits of blossoms that were pistil-inoculated with PBS were used as negative controls. Seed germination percentages and BFB seedling transmission percentages ((number of seedlings with BFB symptoms divided by the total number of seeds germinated) × 100) were recorded at 14 days after planting (DAP). Additionally, mean A. citrulli CFU/seed for samples (n = 30 seeds) from each lot were determined by ten-fold serial dilution of individually macerated seeds followed by spread-plating onto Nunhem’s semi-selective agar (Nunhems Seed Company, Haelen, The Netherlands). After incubation for 5 - 6 days at 28oC, A. citrulli colonies were enumerated and mean CFU/seed was determined for each lot.
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