First report of Peronospora lamii, downy mildew on basil ( Ocimum basilicum) in Belgium. First report of the occurrence and resistance to Mefenoxam of Peronospora belbahrii, causal agent of downy mildew of basil ( Ocimum basilicum) in Israel. Evidence for resistance to metalaxyl in isolates of Peronospora hyoscyami. Resistance against basil downy mildew in Ocimum species. Phylogenetic analysis and real time PCR detection of a presumably undescribed Peronospora species on sweet basil and sage. belbahrii inoculum in the field through seeds infected by resistant strains.īelbahri, I., Calmin, G., Pawlowski, J., & Lefort, F. This study provides new information on the potential risk of introducing mefenoxam-resistant P. belbahrii were completely controlled by the field dosage of both chemicals also 14 days after the last treatment. Three out of four DM populations from seeds and two out of three from basil plants were found to be able to infect basil plants in the presence of 100 μg/ml and 200 μg/ml of mefenoxam, while the field dosage of azoxystrobin (186 μg/ml) was found to be completely effective. Azoxystrobin was used at the field dosage as the chemical control. Basil plants were inoculated with a sporangial suspension of seven DM populations and treated, before and after inoculation with the pathogen, with different dosages of mefenoxam: 100 μg/ml, which corresponds to the currently applied field dosage, 200 μg/ml and 1000 μg/ml. DM populations from basil plants and seeds, which are associated with failure in downy mildew control under field and greenhouse conditions, have been tested for their sensitivity to mefenoxam. The use of light breaks during the darkness period could be one piece of a strategy against downy mildew epidemics on basil in greenhouses.Epidemics of basil downy mildew (DM) incited by Peronospora belbahrii have been very severe in Italy since 2013, in part due to the very favorable weather conditions, and losses have occurred in many commercial farms, even after repeated mefenoxam treatments. We therefore conclude that it is possible to influence the epidemiology of basil downy mildew with light. It seems that downy mildew of basil needs a period of darkness for the induction of sporulation. Treatments in which the 10 h darkness period was interrupted with light (either 3 h darkness (D), 4 h light (L), 3 h darkness or 2 h D/2 h L/2 h D/2 h L/2 h D) showed either reduced or no sporulation. While the negative control with 24 h of light showed no sporulation at all, there was full sporulation in the positive control (14 h light, 10 h darkness). There was a clear influence of light intervals on incidence and severity of sporulation of basil downy mildew. Disease assessment was 10 to 16 days after inoculation. Subsequently, plants were moved to the growth chamber with different light regimes (same temperature and humidity but different intervals of artificial light and darkness). Plants were spray inoculated with sporangia and incubated in a humidity chamber. To assess the influence of different light intervals on the sporulation of downy mildew on basil, a series of experiments were conducted under controlled conditions. Under optimal conditions, dense mats of black sporangia are produced on the abaxial side of the leaves, creating a high epidemic potential.įor some oomycetes, it is known that they show a direct reaction to light.įor Plasmopara viticola, it was shown that under continuous light there was no formation of sporangia a dark period is needed to induce sporulation. Generally, infection of new plant tissue occurs by zoospores released from sporangia. Downy mildew of basil ( Ocimum basilicum), caused by the pathogen Peronospora belbahrii, seriously affects greenhouse production of basil in Europe.
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