First Report of Downy Mildew Caused by a Peronospora sp. on Basil in Florida and the United States

Abstract

Basil is grown as a specialty crop in greenhouse and field production in Florida and other regions of the United States. Downy mildew on basil (Ocimum basilicum) was detected from four production sites (Collier, Hendry, Miami-Dade, and Palm Beach counties) in south Florida in the fall of 2007, and within months, it was also found in west-central north Florida (Hillsborough County). Incidence reached nearly 100% on some of the affected crops and caused complete yield losses on basil grown both in the field for fresh market and potted herbs market. Symptoms developed during transit on basil that appeared symptomless at harvest. Symptoms initially appeared as yellowing on the lower leaves that was typically delineated by the veins, although in some cases the entire leaf area of the leaf surface was affected. A gray, fuzzy growth was apparent on the abaxial leaf surface. Microscopic observation detected dichotomous branching, hyaline sporangiophores (220 to 750 × 4 to 9 μm) bearing single sporangia. Sporangia were light brown, ovoid to slightly ellipsoid, and measured 14 to 15 × 15 to 18 μm. Oospores were not observed. Leaves of potted basil plants and coleus (Solenostemon scutellarioides) were inoculated with a suspension containing 1 × 105 sporangia/ml and sprayed till runoff (approximately 15 ml per plant) with a hand-held pressurized aerosol canister. Plants were covered with a plastic bag for 24 h and maintained in the greenhouse under ambient conditions. Noninoculated plants served as controls. After 7 days, symptoms typical of downy mildew occurred only on the inoculated basil plants and sporulation was confirmed microscopically. The internal transcribed spacer regions of an isolate collected in Hendry County were sequenced bidirectionally. The consensus sequence was deposited into GenBank (Accession No. FJ346561). Sequence data matched (100% homology) with a Peronospora sp. reported on sweet basil in Switzerland (GenBank Accession No. AY884605) and was similar (99% homology) to an isolate (GenBank Accession No. DQ523586) reported on coleus, although inoculation to coleus failed to confirm pathogenicity on this host. The sequence data also distinguished the isolate from P. lamii (87% homology) previously reported to occur on basil. The pathogen was identified as a Peronospora sp. based on morphological characteristics and sequencing homology (1–3). References: (1) L. Belbahri et al. Mycol. Res. 109:1276, 2005. (2) S. Francis. CMI Descriptions of Pathogenic Fungi and Bacteria. No. 688. CMI, Kew, England, 1981. (3) A. McLeod et al. Plant Dis. 90:1115, 2006.

Efficacy of Acibenzolar‐S‐Methyl and β‐Aminobutyric Acid for Control of Downy Mildew in Greenhouse Grown Basil and Peroxidase Activity in Response to Treatment with these Compounds

“…In the United States, basil downy mildew has spread rapidly because its first report from South Florida in the fall of 2007 (Roberts et al. ). The disease has been reported in many northern, south‐eastern, central and pacific states of the United States including the Hawaiian Islands (Anonymous ; McGrath ), and it caused losses as much as 100% on some US farms (Wyenandt et al.…”

Rapid staining method to detect and identify downy mildew (Peronospora belbahrii) in basil

“…High disease severity can cause complete crop loss in both the greenhouse and field (Roberts et al, 2009; Wick and Brazee, 2009). Downy mildew has been reported to also infect several species of the Lamiaceae family including sage, coleus, and basil (Choi et al, 2009; Thines et al, 2009).…”

Red Light Increases Suppression of Downy Mildew in Basil by Chemical and Organic Products

“…In recent years, high demand and high dollar value of fresh market basil lead to increased field and greenhouse production of basil (Dekalb et al 2014;Wyenandt et al 2015). In the United States, downy mildew of basil was first detected in Homestead, Florida, in 2007 (Roberts et al 2009). In the United States, downy mildew of basil was first detected in Homestead, Florida, in 2007 (Roberts et al 2009).…”

“…However, downy mildew caused by Peronospora belbahrii has become destructive for basil production worldwide (Garibaldi et al 2004(Garibaldi et al , 2005; Mart ınez de la Parte et al 2010;McGrath et al 2010;McLeod et al 2006;Nagy and Horv ath 2011;Ronco et al 2008;Voglmayr and Piątek 2008;Wyenandt et al 2015). In the United States, downy mildew of basil was first detected in Homestead, Florida, in 2007 (Roberts et al 2009). Since then, downy mildew of basil has been reported in more than 42 US states including Hawaii and Alaska (Wyenandt et al 2015).…”