Temperature Effect on Seed Germination in Spinach (Spinacia oleracea L.)

The economic value of spinach (Spinacia oleracea L.) continues to increase both in the United States and globally. In order to meet increasing demand, spinach production must be improved so that spinach may be grown in alternate seasons and locations, or in greenhouse and high tunnel as a year-round vegetable. Breeding spinach for heat tolerance is necessary for the improvement of spinach production, and seed germination is the first stage to test and to screen in order to develop heat-tolerant spinach lines. The objective of this research was to determine temperature effect on the seed germination rate, and to select heat tolerant spinach lines. A total of 41 spinach lines were studied. The germination experiment 1 was conducted using five controlled treatment temperatures: 20^oC, 24^oC, 28^oC, 32^oC, and 36^oC in growth chambers using completely randomized design with 3 replicates. For each spinach line, 50 seeds were placed in a single 9-cm petri dish lined with blotter paper totaling 150 seeds per treatment. The dishes were moistened with 3.5 mL of double distilled water and wrapped with Parafilm M sealing film to minimize water loss. Seeds were considered germinated when 1 mm of radical had emerged through the pericarp. Germinated seeds were counted on seven day intervals beginning on the seventh day after sowing and continuing through 21 days. In experiment 2, lines that exhibited high germination rate at high temperatures in experiment 1 were tested again under four temperature treatments; 20^oC, 32^oC, 36^oC, and 40^oC. Germinated seeds were counted on a 72-hour interval. It is expected that several lines will be identified for heat tolerant germination and these will be directly used in spinach production or will serve heat-tolerant parents in spinach heat-tolerant breeding and selection.