First Report of Downy Mildew on Basil (Ocimum basilicum) in Italy

Abstract

Sweet basil (Ocimum basilicum) is an economically important herb in several Mediterranean countries. Approximately 80 ha are grown annually in Italy for fresh and processed consumption. In 2003, a damaging foliar disease was observed in several greenhouses located in the Liguria Region of northern Italy. More that 50% of the plants were affected. 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 surface of infected leaves. These symptoms sometimes occurred on the top sides of leaves. Although the distribution of the disease was generally uniform, symptoms appeared first in a patchy pattern in the central part of the greenhouses where air temperature and relative humidity were highest. Where air circulation was apparently poor, bottom leaves were severely affected by the disease. Microscopic observations revealed conidiophores branching two to seven times. Conidiophores with a length of 250 to 500 μm (average 350 μm) ended with sterigmata bearing single conidia. Conidia measured 15 to 25 × 20 to 35 μm (average 22 × 28 μm) and were elliptical and grayish in mass. The pathogen was identified as a Peronospora sp. based on its morphological characteristics (3). Pathogenicity was confirmed by inoculating leaves of 40-day-old healthy plants with a conidial suspension (1 × 105 conidia per ml). Three containers containing 150 plants each of O. basilicum cv. Genovese gigante were used as replicates. Noninoculated plants served as controls. Inoculated and noninoculated 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 a Peronospora sp. was observed on the leaves. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of a Peronospora sp. on basil in Italy. Peronospora sp. and P. lamii were previously reported on sweet basil in Uganda (1,2). References: (1) C. G. Hansford. Rev. Appl. Mycol. 12:421, 1933. (2) C. G. Hansford. Rev. Appl. Mycol. 17:345, 1938. (3) D. M. Spencer. The Downy Mildews. Academic Press, N.Y., 1978.

Identification and histopathology of the foliar nematode Aphelenchoides ritzemabosi (Nematoda: Aphelenchoididae) on basil in Italy

“…Unfortunately these characteristic symptoms can be easily confused with those caused by other foliar pathogens, such as the causal agent of basil downy mildew (Peronospora sp.) (Garibaldi et al, 2004) and basil black spot (Colletotrichum sp.) (Gullino et al, 1995).…”

“…infections are carefully evaluated, not only on symptomatology, but also on the basis of microscopic observations. Both of the fungal diseases can usually be recognised on the basis of the morphological characteristics of the asexual fruiting bodies (Gullino et al, 1995;Garibaldi et al, 2004), while nematode infection must be determined by dissecting symptomatic material and identifying the emerging nematodes to species level.…”

Seed dressing to control downy mildew of basil

“…Italiano classico (Furia Sementi) of basil, highly susceptible to downy mildew, belonging to the same lot which showed to be naturally contaminated by P. belbahrii in previous trials, were used. The seed lot used in the trials was selected because showed 7-15% of infected basil plants under completely controlled environment conditions in growth chamber at 22°C (12 h day fluorescent light regime), 15-21 days after sowing (Garibaldi et al 2004a). The seed sample was stored at 8°C to maintain seed a stable infection level before starting each trial.…”

“…(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.…”

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).…”