The 2012 ASHS Annual Conference

Micronutrients are required for growth of human body and for maintaining good health.  Zinc (Zn) is a minor element for human nutrition, and Zn-rich vegetables will help to provide this nutrition. This study determined the potential to increase Zn density of lettuce (Lactuca sativa L.) through cultivar selection and nutrient management. Twelve cultivars including butterhead, romaine, and loose-leaf phenotypes of heritage and modern genetics were tested in a greenhouse experiment. Organic fertilizer (3-1.5-2) and Hoagland no. 1 solution factored with three elevated Zn levels (0.05, 0.10, and 0.15 mg/L) were the fertilizer regimes with Zn provided as ZnSO₄. Zinc in whole shoots was analyzed by atomic absorption spectrophotometry on oven-ashed samples. Modern cultivars had a significantly higher fresh weight yield (32%) than heritage cultivars but accumulated a slightly lower Zn concentration (65 mg/kg dry wt) than heritage cultivars (67 mg/kg dry wt). Butterhead phenotypes had a lower yield (38%) than loose-leaf but had the highest Zn concentration (78 mg/kg dry wt) followed by romaine (66 mg/kg dry wt) and loose-leaf (53 mg/kg dry wt). Accumulation of Zn did not differ between fertility regimes with accumulation being 66 mg/kg dry wt with the organic regime and 65 mg/kg dry wt with Hoagland solution. Elevated Zn level within the fertility regimes also had only small effects on tissue Zn with the concentrations being 65 mg/kg dry wt at 0.05 or 0.10 mg/L and 66 mg/kg dry wt at 0.15 mg/L. Differences in Zn concentrations was significant among individual cultivars with ranges from 91 mg/g dry wt  to 42 mg/kg dry wt Zn. ‘Tom Thumb’, ‘Adriana’, ‘Claremont’, and ‘Focea’ were the top in cultivar ranking with mean Zn concentration of 63 mg/kg dry wt, whereas ‘Two Star’, ‘Black Seeded Simpson’ ‘Simpson Elite’, and ‘Winter Density’ were low accumulators with a mean of about 51 mg/kg dry wt. Fresh wt of cultivars had a negative correlation with accumulation of Zn concentration. The results of the experiment signify that selection of elevated nutrient regimes and cultivars may be utilized to increase Zn accumulation in lettuce.