Peronospora arborescens Causes Downy Mildew Disease in Commercial Opium Poppy Crops in France

Abstract

Opium poppy is a strategic crop for the pharmaceutical industry because it is the only source of morphine, codeine, and thebaine alkaloid drugs. Approximately 7,360 ha (average from 2001 through 2007) of opium poppy (Papaver somniferum) are grown annually in France, mainly in the Northern-East (Champagne-Ardenne) and Centre-West (Centre and Poitou-Charentes) regions of the country. This acreage accounts for nearly 5.6% of the legally cultivated opium poppies worldwide. Disease symptoms resembling those of downy mildew (2) have been observed frequently in those opium-poppy-growing areas, especially in the Charente-Maritime, Cher, Loiret, and Loir et Cher departments. Disease symptoms included chlorotic to light yellow lesions on the leaf blade, curling and thickening of affected tissues, and expanding necrotic lesions that coalesced, eventually giving rise to large necrotic areas or death of the entire leaf tissues and the plant. With wet weather or high relative humidity, sporangiophores with sporangia were produced frequently on the abaxial leaf surface and occasionally on the adaxial side. Peronospora arborescens and P. cristata have been demonstrated as causal agents of opium poppy downy mildew disease and both have been reported in Europe (1–3); however, the specific identity causal agent in commercial opium poppy crops in France has not yet been determined. Microscopic observations of affected leaves in symptomatic opium poppy leaves sampled from three commercial fields in Loiret Department revealed dichotomously branching sporangiophores bearing single sporangia and oospores of shape and measurements similar to those reported for P. arborescens and P. cristata (1,3). Sporangia dimensions of P. arborescens and P. cristata overlapped, making it difficult to differentiate between the two species based solely on morphological characters (3). A species-specific PCR assay protocol (2) that differentiated P. arborescens from P. cristata was used to diagnose the pathogen. Also, the sequence of the complete 5.8S ribosomal DNA gene and internal transcribed spacers (ITS) 1 and 2 were determined and maximum parsimony analysis was performed with the Peronospora spp. data set described by Landa et al. (2). Both species-specific PCR and phylogenetic analyses of ITS sequences showed that P. arborescens was the only Peronospora species associated with the three samples of downy-mildew-affected leaves analyzed. Thus, DNA fragments of 545, 594, and 456 bp were amplified using total DNA extracted from the sampled leaves and P2, P3, and P6 primer pairs (2), respectively. ITS sequences of all three samples showed 100% homology (GenBank Accession No. EU295529). Phylogenetic analyses using Neighbor Joining of those sequences placed the infecting Peronospora sp. in a clade (100% support) that included all P. arborescens sequences from the GenBank database with 99.2 to 99.9% homology among sequences (2,3). To our knowledge, this is the first report and molecular evidence that P. arborescens causes downy mildew disease in commercial opium poppy crops in France. References: (1) S. M. Francis. No. 686 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1981. (2) B. B. Landa et al. Phytopathology 97:1380, 2007. (3) J. B. Scott et al. Phytopathology 93:752, 2003.

Short communication: Local infection of opium poppy leaves by Peronospora somniferi sporangia can give rise to systemic infections and seed infection in resistant cultivars

“…Attacks by the disease are also of social significance because opium poppy is the only source of codeine, morphine and thebaine drugs for the pharmaceutical industry, which are key components for alleviation of chronic pain associated with cancer diseases. Until very recently, P. somniferi and P. meconopsidis have been referred in the phytopathological literature as P. arborescens (Kapoor, 1995;Bajpai et al, 1999;Landa et al, 2005;Montes-Borrego et al, 2008;Dubey et al, 2009) and P. cristata (Scott et al, 2004), respectively. However, the taxonomic status of the latter two species was recently clarified by means of molecular analyses in conjunction with morphological characteristics (Voglmayr et al, 2014).…”

Molecular insights into enhanced resistance of Papaver somniferum against downy mildew by application of endophyte bacteria Microbacterium sp. SMR1

“…Downy mildew adversely affects the formation of capsules, hence reducing the yield of opium. The adverse effect of downy mildew on P. somniferum cultivation has also been reported in other parts of the world, including Spain, France, and Australia (Cotterill & Pascoe, 1998;Landa et al, 2005;Montes-Borrego et al, 2008). Downy mildew is a severe threat to the sustainable cultivation of P. somniferum, and opium production.…”