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  • Author or Editor: Michael Thornton x
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Abstract

Experiments were conducted to determine if changes in tuber ascorbic acid content following bruising were related to blackspot susceptibility in potato (Solanum tuberosum L.). Tubers of four potato clones were bruised at three locations. Ascorbic acid content of bruised and nonbruised tissue on the same tubers was determined 0, 3, 6, 12, and 24 hr after bruising. Differences in initial ascorbic acid content between clones were highly significant, but not related to blackspot susceptibility. Differences in ascorbic acid content between bruised and nonbruised tissue of a tuber were significant in two of the four clones. Changes in ascorbic acid content of tubers with time occurred to a similar extent in bruised and nonbruised tissue. This experiment indicates that factors other than ascorbic acid content may determine differences in clonal susceptibility to blackspot.

Open Access

A field study was conducted to determine the relationship between pungency, soluble solids content, and susceptibility to neck rot in onions. `Golden Cascade', `Sweet Amber', `Valdez', and `Vega' onions were planted in a field with low soil S content. Sulfur, as coarse-ground calcium sulfate, was applied as a band before planting. After harvest, yield was determined and a sample of jumbo onions was taken from each plot to determine pungency, dry matter content, and soluble solids content. Healthy bulbs were returned to storage and evaluated for neck rot after 4 months. Yield, grade, and neck rot incidence after storage were not affected by S treatments. However, there was a trend toward lower neck rot incidence at the highest S application rate (160 lb/acre). Pungency of jumbo onions increased after the application of S as gypsum. `Sweet Amber' and `Valdez' were less pungent than `Golden Cascade' or `Vega'. Neck rot susceptibility was evaluated with an inoculation test of detached bulb scales. Growth and sporulation of the neck rot pathogen Botrytis allii were reduced by S application. Pungency and neck rot susceptibility were negatively correlated.

Free access

Pathogen populations, disease development and onion yield were compared in solarized, fumigated and non-treated plots during 1992 and 1993. Soil solarization was accomplished by covering plots with clear plastic for six weeks beginning in mid-August, prior to the year of onion production. Solarization was also combined with metham sodium, a plied prior to covering with plastic. Soil temperatures reached a maximum of 48°C at the 10 cm depth in solarized plots, and were consistently 10 to 15°C higher than in non-solarized plots. Disease resistant (Bravo) and susceptible (Valdez) onion cultivars were planted the following spring. Only the solarization + metham sodium treatment significantly controlled pink root and plate rot in 1992. In 1993, all solarization and fumigation treatments controlled pink root. Solarization and fumigation did not significantly increase yield in comparison to the check, except for the solarization + metham sodium treatment in 1992. Bravo exhibited lower disease incidence than Valdez in both years of the study. Bravo produced 32.7 t/ha and 6.2 t/ha higher yield than Valdez in 1992 and 1993, respectively.

Free access