ISHS Acta Horticulturae 747: VIII International Symposium on Protected Cultivation in Mild Winter Climates: Advances in Soil and Soilless Cultivation under Protected Environment
PHYLOGENETIC ANALYSIS AND REAL TIME PCR DETECTION OF A NEW PERONOSPORA SPECIES RESPONSIBLE FOR DOWNY MILDEW DISEASE OF SWEET BASIL AND SAGE |
| Authors: | L. Belbahri, G. Calmin, F. Lefort, J. Pawlowski |
| Keywords: | Ocimum sativum |
| Abstract:
Downy mildew of sweet basil (Ocimum basilicum) has become a serious disease issue for the producers of sweet basil in Switzerland since it was first recorded in 2001 and became prevalent, affecting most plants each season. The pathogen can spread rapidly throughout plants, under conditions of high humidity and cool temperatures, causing complete crop losses in some greenhouses. In the past years, based on epidemiological data and microscopic observations, the pathogen responsible for downy mildew disease on Lamiaceae was reported as Peronospora lamii or Peronospora sp. in Austria, Benin, France, Italy, Israel, New-Zealand, Switzerland and the US. Its preferential hosts belong to the Lamiaceae family including basils (Ocimum spp.), mints (Menta spp.), sages (Salvia spp.) and other aromatics. This study investigated the taxonomic status of this new downy mildew pathogen, using both morphological characters and molecular analysis of the internal transcribed spacer (ITS) region of the ribosomal DNA (rDNA). The inherent variability of conidial dimensions made species differentiation difficult, though conidia of the new Peronospora sp. were usually larger than those of P. lamii. Sequence homology and phylogenetic analysis of nine samples collected on sweet basil from different locations, showed unique ITS sequences sufficiently distinct from those of any described Peronospora species, especially P. lamii. Molecular phylogeny showed that the new downy mildew pathogene was a Peronospora species unrelated to P. lamii. In order to facilitate the detection of this new pathogen from infected tissues or seeds, PCR primers for real time PCR analysis were developed. These primers can also be used in classic PCR. Specific PCR primers for Peronospora lamii were also developed for comparison purposes. | |
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