First Report of Downy Mildew Caused by Peronospora sp. on Basil (Ocimum basilicum) in France

Abstract

Sweet basil (Ocimum basilicum) is an economically important herb in several Mediterranean countries. Approximately 30 ha are grown annually in France for fresh and processed consumption. During the spring and fall of 2004, a damaging foliar disease was observed in some crops near Saint Tropez in the French Riviera Region. More than 50% of plants were affected in an organically produced field-grown crop at an altitude of 250 m. Leaves of infected plants were initially slightly chlorotic, especially near the central vein. Within 2 to 3 days, a characteristic gray, furry growth was evident on the lower leaf surface and sometimes on the upper leaf surface. The appearance and severity of the disease was affected by overhead sprinkler irrigation. Basal leaves were severely affected. Microscopic observations revealed sporangiophores branching two to seven times. Sporangiophores, with a length of 250 to 500 μm (average 350 μm), ended with sterigmata bearing single sporangia. Sporangia measured 15 to 25 × 20 to 35 μm (average 22 × 28 μm), were elliptical and grayish in mass. The pathogen was identified as Peronospora sp. on the basis of its morphological characteristics (4). Pathogenicity was confirmed by inoculating leaves of 40-day-old healthy plants with a sporangial suspension (1 × 105 conidia/ml). Three containers with 150 plants each of O. basilicum cv Genovese gigante were used as replicates. Noninoculated plants served as controls. Plants were maintained in a growth chamber at 20°C (12 h of light per day) and 90 to 95% relative humidity. The pathogenicity test was carried out twice. After 6 days, typical symptoms of downy mildew developed on the inoculated plants, and Peronospora sp. was observed on the leaves. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of Peronospora sp. on basil in France. Peronospora sp. was previously reported on sweet basil in Italy (1) and P. lamii on sweet basil in Uganda (3). Seed transmission (2) is suspected as the reason for recent outbreaks in Europe. References: (1) A. Garibaldi et al. Plant Dis. 88:312, 2004. (2) A. Garibaldi et al. Z. Pflanzenkr. Pflanzenschutz 111:465, 2004 (3) C. G. Hansford. Rev. Appl. Mycol. 12:421, 1933. (4) D. M. Spencer. The Downy Mildews. Academic Press, NY, 1981.

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

“…The disease was first discovered in Uganda in 1933 (Hansford ), and its devastating impact has recently been reported from many countries (Garibaldi et al. , ; Martínez‐de la Parte et al. ; McLeod et al.…”

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

“…Basil, primarily sweet basil, is used for fragrance, flavour, fresh culinary and dried herb industries (Simon et al 1990(Simon et al , 1999. 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). 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).…”

Seed dressing to control downy mildew of basil

“…(Hansford, 1933) and later, in the 2000s, reported as responsible of increasingly serious losses in several countries, starting from Switzerland (Lefort et al 2003), Italy (Garibaldi et al 2004a), Belgium (Coosemans, 2004), France (Garibaldi et al 2005), and including USA (Roberts et al 2009), Cuba (Martinez de la Parte et al 2010), and Hungary (Nagy and Horvath, 2011). Nowadays, downy mildew has been observed wherever basil is grown as herb crop as well as for pesto sauce production.…”