In the northeastern United States, increased interest in season extension combined with high demand for fresh vegetables in spring provides a possible market for hardy overwintering fresh market vegetables. In Great Britain, WSB is a biennial crop that is planted in late summer, overwinters, and is harvested in winter and early spring. In this report, we explore the potential for WSB production as a new crop for early spring production in New England.
The term “broccoli” is used to describe a wide array of types of cultivated accessions of Brassica oleracea. Broccolis may be “sprouting” or “heading,” depending on the degree of branching exhibited and the size of the inflorescences. Further, accessions vary in sepal color (green, purple, and white) and life cycle (annual, biennial, and perennial) (Gray, 1989; Whealy, 2004).
In the United States, annual green heading broccoli (B. oleracea var. italica), known as calabrese in Europe, is widely grown. In the 1980s, calabrese was the only B. oleracea var. italica vegetable to be extensively developed by crop breeding and to be represented by numerous cultivars including both open-pollinated and F1 hybrid cultivars (Gray, 1989). It has been selected for rapid maturity, an annual habit, increased head size, and a decrease in lateral shoot development. The crop is now recognized as a heading vegetable rather than a sprouting vegetable (Crisp and Gray, 1985). These characteristics distinguish calabrese from the purple- and white-sprouting broccolis that are biennial in habit, are cultivated for lateral shoot development, and bear white, yellow, or green cauliflower curds or clusters of young flower buds whose sepals may be green or purple (Gray, 1989).
Annual sprouting brassicas currently grown in the United States include broccoli raab (Brassica rapa ssp. rapa) and broccolini, a cross between heading broccoli and chinese kale or gai-lan (Brassica alboglabra) (Cintas et al., 2002; Livingston, 2010). The former has a pungent mustard green flavor, and the latter is proprietary and not available for independent market gardeners to grow (Livingston, 2010). By contrast, the mild-flavored WSB (B. oleracea var. italica) is a biennial crop that is popular in Great Britain, but relatively unknown in the United States.
While peer-reviewed literature is widely available specific to heading broccoli, there is very little that specifically addresses WSB. The sprouting broccolis are documented in writings from the 16th century when, according to Nieuwof (1969), Delachamp described sprouting broccoli under the name Brassica asparagoides. Miller’s Gardener’s Dictionary of 1724 also refers to a “sprout cauliflower” and “Italian asparagus” (Gray, 1982). Vilmorin-Andrieux (1885) also describes “Purple Sprouting” or “Asparagus Broccoli.” The crop may be much older; Buck (1956) proposes that the terms “asparagus broccoli,” “sprouting broccoli,” and “Christmas Calabrian broccoli” are synonymous with the “Bruttium broccoli” described by the naturalist Pliny, who lived in Italy from in the first century CE.
Until recently, purple and white WSB cultivars were primarily maintained by mass selection and were thus highly variable and considered unworked crops (Gray, 1982). Crisp and Gray (1985) characterized WSB as widely popular with amateur growers and easy to grow but unpopular with commercial growers because of poor uniformity, inconsistent maturity time, and overall quality of the marketed product thus resulting in high harvest costs. However, WSB received high market prices because of popularity with consumers. Crisp and Gray (1985) also noted a short harvest season and observed that time to maturity is largely governed by temperature. This caused harvest to be sporadic in March and early April building to a peak in late April to May and then ceasing abruptly. These were considered poor conditions for marketing and also difficult conditions for maintaining consumer interest. In a response, breeding programs were undertaken to improve biennial sprouting broccoli (Crisp and Gray, 1985; Crisp et al., 1985; Gray, 1982).
Crisp and Gray (1985) acknowledge three categories of WSB: purple-sprouting, early maturing white-sprouting, and late-maturing white-sprouting. According to Gray (1989), purple and early white WSB cultivars are classified as broccoli (B. oleracea var. italica) and late white WSB cultivars, with their relatively undifferentiated flower buds, are classified as cauliflower (B. oleracea var. botrytis). The purple-sprouting cultivars bore tight purple florets and early white-sprouting cultivars bore small loose clusters of pale yellow or pale green flower buds on long fleshy side shoots. The late-maturing white-sprouting cultivars were morphologically homogenous with short leafy side shoots bearing small compact white curds. The purple and early white cultivars were found to be broadly similar, with late white cultivars distinguished by later maturity and greater yield per plot (Crisp et al., 1985).
The improved genotypes selected by Crisp and Gray (1985) were released to Elsoms Seeds (Spalding, UK) and Tozers Seeds (Cobham, UK), two major commercial seed providers in England (D. Pink, personal communication). Elsoms Seeds currently maintains a breeding program as a joint venture with Bejo Zaden of Warmenhuizen, The Netherlands (Elsoms Seeds, 2008) and F1 hybrids are currently available. A limited number of these are currently commercially available in the United States; however, we are aware of no published research that addresses production of this crop in the United States.
Most of the United Kingdom has average annual minimum temperatures ranging from −10 to −5 °C, which corresponds to U.S. Department of Agriculture (USDA) USDA hardiness zones 8a–9a (Rice, 2010). In comparison, much of the northeastern United States falls within hardiness zones 3a–7b. It is reasonable to assume that season extension techniques might be required to overwinter the crop in New England, but the extent of protection required is unknown. The use of high or low tunnels covered with plastics, spunbonded, or woven rowcovers, or a combination thereof, are known to moderate harsh winter climates without supplemental heating (C.A. Martin and R.G. Sideman, unpublished; Lamont, 1996; Lamont et al., 2003; Takeda et al., 2008; Wells, 1996; Wien, 2009). We hypothesized that the use of high tunnels, with or without supplemental low tunnels, would permit WSB to survive the harsh New England winters to produce spring crops.
In 2006–07 and 2007–08, several WSB cultivars were transplanted into unheated high tunnels with and without supplemental rowcover in Durham, NH. Results from these pilot experiments suggested that factors such as rowcover, planting date, and cultivar affected yield, time to maturity, and the length of harvest season. High levels of mortality were observed for WSB plants grown in high tunnels without supplemental rowcover, suggesting that additional protection inside a high tunnel would be needed (R.G. Sideman, unpublished). In this manuscript, we report the results of subsequent experiments aiming to identify cultivars and cultural practices suitable for producing WSB in New England winter conditions. Specifically, we sought to evaluate cultivars currently available in England to determine comparative yields when grown overwinter in an unheated high tunnel in Durham, NH. In addition, use of secondary low tunnels within the high tunnel was examined for effect on yield, duration of harvest, and the number of days to harvest.
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