New Disease Reports
New Disease Reports (2009) 20, 18.
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First report of Peronospora sp.on sweet basil (Ocimum basilicum) in Cuba

E. Martínez-de la Parte 1, L. Pérez-Vicente 2*, B. Bernal 3 and D. García 1

*lperezvicente@live.com

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Accepted: 30 Nov 2009

In Cuba, sweet basil (Ocimum basilicum) is used fresh, dried and processed for flavouring and fragrances, and as insect repellent in greenhouses. In February 2009 a foliar disease was observed in plots of sweet basil cv. “Genovesa”, located at the Horticulture Research Institute “Liliana Dimitrova” in Quivican, Havana province, and in greenhouses for vegetable production in Siboney, Havana City, Cuba . Leaves of infected plants were initially slightly chlorotic, especially near the central vein (Fig. 1 A, B). Within two to three days, a characteristic grey downy growth was evident on the lower surface of infected leaves (Fig. 2). Microscopic observations revealed conidiophores 2-7 times dichotomously branched, with length 250 - 500 μm (average 350 μm) and sterigmata bearing a single conidium (Fig.2). Conidia measured 25-35 x 20-28 μm (average 30 x 24 μm) and were elliptical and greyish in mass (Figs. 3A and B). No oospores were found.

Pathogenicity tests were carried out twice by inoculating leaves of 40-day-old healthy plants of sweet basil and sage (Salvia officinalis) with a conidial suspension (1x105 conidia/ml). Non-inoculated plants served as controls. After six days, typical symptoms of downy mildew developed only in the inoculated plants of sweet basil, and Peronospora-type conidiophores were observed developing on the leaves.

Two species of Peronospora have been associated with sweet basil: Peronospora lamii (Coosemans, 2004; Belbahri et al., 2005) and Peronospora sp. (Garibaldi et al., 2004; Belbahri et al., 2005). P. lamii has conidia in the range 16-26 x 15-23 μm (average 21 x 18 μm) and the dimensions reported for the unnamed Peronospora sp. conidia were 20-35 x 15-25 μm (Belbahri et al., 2005) and 23-36 x 18-29 μm (Garibaldi et al., 2005). Additionally, the unnamed Peronospora species is not pathogenic on Salvia officinalis, on which P. lamii causes downy mildew (Garibaldi et al., 2005). The conidiophores and conidia of the Cuban samples of Peronospora sp. found in sweet basil were similar in shape, color, and size range as the previously unnamed Peronospora sp. reported by Garibaldi et al. (2005) and are not pathogenic to sage. This pathogen had previously been reported in Italy and France (Garibaldi et al., 2005). This is the first report of a Peronospora sp. on sweet basil in Cuba .

Figure1+
Figure 1: Disease symptoms of Peronospora sp. on sweet basil (A) on the plant and (B) on individual leaf
Figure 1: Disease symptoms of Peronospora sp. on sweet basil (A) on the plant and (B) on individual leaf
Figure2+
Figure 2: Peronospora sp. conidiophore and conidia on the underside of the leaves
Figure 2: Peronospora sp. conidiophore and conidia on the underside of the leaves
Figure3+
Figure 3: Conidiophore with conidia at two different magnifications: (A) bar = 30 µm (B) bar = 100 µm
Figure 3: Conidiophore with conidia at two different magnifications: (A) bar = 30 µm (B) bar = 100 µm

References

  1. Belbahri L, Calmin G, Pawlowski J, Lefort F, 2005. Phylogenetic analysis and Real Time PCR detection of a presumably undescribed Peronospora species on sweet basil and sage. Mycological Research 109,1276-1287.
  2. Coosemans J, 2004. First report of Peronospora lamii, downy mildew on basil (Ocimum basilicum) in Belgium . Parasitica  60, 27.
  3. Garibaldi A, Minuto G,Bertetti D, Gullino ML, 2004. Seed transmission of Peronospora sp. of basil. Journal of Plant Diseases and Protection 111, 465–469.
  4. Garibaldi A, Minuto A, Gullino ML, 2005. First report of downy mildew caused by Peronospora sp. on basil (Ocimum basilicum) in France . Plant Disease 89, 683.
This report was formally published in Plant Pathology

©2009 The Authors