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TAKE ONE July, 2015
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TAKE ONE No. 147
The Basil Battle: New Cultivars on the Horizon to Beat Downy Mildew By Tom Castronovo Executive Editor
Jack Rabin/Photo
Rutgers Professor James E. Simon, left, and Rutgers plant breeding Ph.D. student Rob Pyne in the Rutgers NJAES Research Greenhouse.
For the past seven years, a familiar scenario has been playing out on farms and in gardens across the United States. A healthy, fragrant crop of sweet basil begins to display yellowing leaves. Upon closer inspection, the undersides of the leaves show signs of a menacing grayish sporulation. It is only a matter of time before the basil plant and others in proximity succumb to this new disease of basil, downy mildew. Neither a fungus nor a mold, downy mildew is the common name for a group of highly specialized plant pathogens called “oomycetes” that infect and feed off living host plants. Each downy mildew is specific to its host plant. For instance, downy mildew of impatiens, another recent scourge, is specific to impatiens, while basil downy mildew affects only basil – with the most popular type, sweet basil, being the most susceptible. Basil downy mildew favors heat and humidity, and by mid- to late-summer, when there is enough inoculum, the disease is widespread in our region. According to Rutgers Extension Specialist in Vegetable Pathology Andy Wyenandt, basil downy
mildew can’t overwinter in our region and can only survive the winter in southern Florida and Texas, where it is a year-round threat. The rapid spread to northern states during the growing season is through the planting of infested seed, by importing southerngrown plant material, or via weather patterns coming from southern states. Plant pathologists have tracked its spread across the U.S. since it was first identified in Florida in 2007. A few years prior, basil downy mildew made its way across Europe after it was initially reported in 2001 in Switzerland. The rapid spread of the disease is intriguing in light of the fact that for decades it was never found beyond the area of its original detection in Uganda in 1933. It has been speculated that the pathogen may have evolved into a more aggressive form and its rapid spread was enabled by seed- and air-borne spore dispersal. The arrival of basil downy mildew in the U.S. has left growers and gardeners flabbergasted and with few options to save their plants. It has required a coordinated effort by agricultural scientists to develop a strategy necessary for battling this new threat, which affects 100 percent of the basil crop. Once basil plants become infected and develop (Continued on Page 22)