Florida is the third largest producer of lettuce in the US. In March and April 2017, lettuces exhibiting signs of wilt and chlorosis were observed in commercial fields in Florida’s Everglade’s Agricultural Area, indicating infection with Fusarium oxysporum f. sp. lactucae (FOL).
Affected fields were planted with the iceberg cultivar Chosen and wilt incidence was as high as 90%. Upon dissection, diseased plants exhibited red-to-brown vascular discoloration in the taproot, and plant death at 30 to 60 days after planting.
"A total of 102 samples were obtained from four different fields. FOL conidia morphology were verified microscopically. The conidial suspensions were used to conduct greenhouse pathogenicity tests on transplanted lettuce seedlings of the susceptible cv. Chosen. Pathogenicity and DNA analysis confirmed the fungal pathogen - explain the scientists at University of Florida Institute of Food and Agricultural Sciences, Belle Glade (FL, USA).
"To our knowledge, this is the first report of FOL in Florida. Fusarium wilt of lettuce was first reported in the US in 1993 in California’s San Joaquin Valley and later in Arizona in 2003.
If FOL continues to increase in Florida, the disease may pose a serious threat to the industry".
Source: Jesse James Murray, Richard Raid, Christian Freedom Miller, German Valentin Sandoya Mirand, 'First Report of Fusarium oxysporum f. sp. lactucae Causing Vascular Wilt of Lettuce in Florida', 28 May 2020, Plant Disease.