High-temperature Inhibition of Seed Germination and Seedling Emergence of Broccoli

in HortTechnology
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  • 1 Graduate Student, Department of Horticulture, Michigan State University East Lansing MI 48824.
  • | 2 Associate Professor, Department of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.
  • | 3 Professor, Department of Crop and Soil Environmental Science, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.
  • | 4 Professor, Department of Agricultural Engineering Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.

High summer temperatures may reduce plant stands of direct-seeded fall broccoli (Brassica oleracea var. italica Plenck). The influence of constant and diurnally alternating temperatures in the range of 5 to 42C on germination and emergence of `Packman' broccoli was evaluated. Germination was defined as protrusion of the radicle from the seedcoat, and emergence as 10 mm elongation of the radicle. The range of constant temperatures from 10 to 30C for 14 days was satisfactory for 90% germination and 75% emergence. However, alternating temperatures extended the acceptable emergence range to 5/17 through 20/32C. Since soil temperatures in warm climates often exceed 20/32C during the summer, high-temperature inhibition of seed germination and seedling emergence is a potentially important factor limiting direct-seeded broccoli stands.