A leafy-green mustard (Brassica juncea L.) cultivar designated Carolina Broadleaf has been released by the Agricultural Research Service of the U.S. Department of Agriculture in 2015. This released cultivar is a narrow genetic-based population of leafy-green mustard derived from a U.S. PI (PI G30988) maintained by the USDA National Plant Germplasm System (NPGS). ‘Carolina Broadleaf’ is a highly uniform mustard in a similar class as the popular cultivar Florida Broadleaf. However, ‘Carolina Broadleaf’ has been selected to exhibit high levels of resistance to a bacterial leaf blight disease caused by Pseudomonas cannabina pv. alisalensis (Pca).
Leafy-green mustards are one type of Brassica “leafy greens” among several other important leafy vegetables, including turnip greens (Brassica rapa L.) and collards and kale (both Brassica oleracea var. acephala). More than 28 million kg of these greens are produced in the United States annually (USDA/NAAS, 2004). Because these crops are grown for the utilization of the foliar portion of the plant, even slight deformity or blemishes of the leaves can result in market rejection and loss of product sales. South Carolina is one of the largest producer of Brassica leafy greens, and average yields for turnip and mustard greens during the summer season have fallen from about 283 boxes/ha to 50 to 58 boxes/ha (1 box = 9 kg) largely due to a leaf blight that emerged in the early 2000s. In 2001, the combined value of turnip and mustard greens produced in South Carolina was $7.1 million. The only formal report (Smith and Keinath, 2005) of economic losses in South Carolina were estimated at up to $1.7 million per year, or 24% of the value of these two crops at that time.
Several bacterial pathogens cause leaf spot and blight diseases of Brassica. The relatively new pathogen Pca has been causing a particularly damaging blight of Brassica leaves. Bacterial blight caused by Pca has now become a significant problem in many Brassica growing areas of the United States, but economic losses for numerous producers in the southeastern United States have been especially severe. Pca has now been reported on numerous crops in most of the leafy greens growing states (Bull et al., 2004a, 2004b; Bull and du Toit, 2009; Koike et al., 2006, 2007; Wechter et al., 2010). Pesticides are not effective against this bacterial disease, and copper has been reported to increase disease incidence (Keinath et al., 2007). Up until now, no commercial mustard green cultivars with significant resistance to Pca have been identified.
‘Carolina Broadleaf’ is the first mustard green cultivar with high levels of resistance to Pca. This cultivar was developed as a possible alternative to the cultivar Florida Broadleaf in areas where Pca is a problem. ‘Carolina Broadleaf’ has been grown and tested by several leafy greens growers and been deemed acceptable for fresh, chopped prepackages, flash frozen, and canned markets.
Bull, C.T. & du Toit, L.J. 2009 First report of bacterial blight on conventionally and organically grown arugula in Nevada caused by Pseudomonas syringae pv. alisalensis Plant Dis. 93 109
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Koike, S.T., Kammeijer, K., Bull, C.T. & O’Brien, R.D. 2006 First report of bacterial blight of romanesco cauliflower (Brassica oleracea var. botrytis) caused by Pseudomonas syringae pv. alisalensis in California Plant Dis. 90 1551
Koike, S.T., Kammeijer, K., Bull, C.T. & O’Brien, R.D. 2007 First report of bacterial blight of rutabaga (Brassica napus var. napobrassica) caused by Pseudomonas syringae pv. alisalensis in California Plant Dis. 91 112
Smith, J.P. & Keinath, A.P. 2005 Crop profile for leafy greens and collards (Fresh Market) in South Carolina. USDA Southern Region Pest Management Center. 21 July 2016. <https://ipmdata.ipmcenters.org/documents/cropprofiles/SCleafygreens.pdf>.
United States Department of Agriculture, National Agricultural Statistics Service (USDA/NAAS) 2004 Vegetable summary. USDA/NAAS, Washington, DC
Wechter, W.P., Farnham, M.W., Smith, J.P. & Keinath, A.P. 2007 Identification of resistance to peppery leaf spot among Brassica juncea and Brassica rapa Plant Introductions HortScience 42 1140 1143
Wechter, W.P., Keinath, A.P., Farnham, M.W. & Smith, J.P. 2010 First report of bacterial leaf blight on broccoli and cabbage caused by Pseudomonas syringae pv. alisalensis in South Carolina Plant Dis. 94 132
Wechter, W.P., Keinath, A.P., McMillan, M.L., Smith, P. & Farnham, M.W. 2013 Expression of leaf blight resistance in Brassica leafy greens under field conditions and inheritance of resistance in a Brassica juncea source Plant Dis. 97 131 137