Evaluation of experimental broccoli hybrids developed for summer production in the Eastern United States

Abstract

Broccoli (Brassica oleracea L. Italica Group) is a vegetable crop requiring relatively cool conditions (e.g., less than 23 °C) to induce and maintain vernalization and to allow normal floral and head development to proceed. In general, this requirement is a major limiting factor to production of broccoli in eastern states where growing seasons are often interrupted by high temperature spikes. The USDA, ARS, U.S. Vegetable Laboratory (USVL) is conducting a program to breed broccoli varieties adapted to summer conditions of the south eastern United States. The goal of the current study was to compare performance of three experimental broccoli hybrids from that program with some commonly raised commercial hybrids ('Packman', 'Marathon', 'Arcadia', 'Greenbelt', 'Patron', and 'Gypsy') by conducting trials in summer environments as well as in more conventional growing environments (e.g., in fall). All hybrids produced marketable heads with high quality ratings in fall field trials (2006, 2007, and 2008). Under the high temperatures that were characteristic of the summer (2007, 2008, and 2009) trials in South Carolina, the commercial hybrids 'Marathon', 'Greenbelt', 'Arcadia', and 'Patron' failed to produce broccoli heads at all. The remaining hybrids produced heads with similar mean head mass, stem diameter, and bead size in South Carolina summer trials. However, the three experimental hybrids produced marketable quality heads, but 'Gypsy' and 'Packman' did not. The primary flaws in 'Gypsy' and 'Packman' heads were increased yellow color, flattening of the dome, increased roughness, and non-uniformity of bead size. In New York trials, all tested hybrids developed heads, but 'Packman' and 'Marathon' produced relatively poor-quality heads when maturing in summer and better quality heads when maturing in the fall. The experimental hybrids exhibited more consistent quality across different maturity times in the New York tests. Results of this research indicate that broccoli response to summer conditions of the eastern United States is dependent on the cultivar grown. Many cultivars are not adapted to extreme summer conditions of the Southeast because they will not be effectively vernalized and will therefore not head. Others such as 'Gypsy' and 'Packman' will head, but non-uniform bud development results in a rough-appearing curd in which flower buds are at various stages of development. The experimental hybrids that are single crosses of in breds selected for adaptation to southeastern summer conditions represent a unique class of broccoli hybrids that combine early maturity and the ability to produce heads under summer conditions of South Carolina. Additional tests of these latter hybrids in New York indicate that they maybe generally adapted to summer environments of the eastern United States.