First Report of Alternaria dauci Causing Leaf Blight of Coriander (Coriandrum sativum) in Algeria

International audienceCoriander (Coriandrum sativum, family Apiaceae) is an important condiment plant in Algeria

Morphological, physiological and pathogenic variability of small-spore Alternaria sp. causing leaf blight of Solanaceous plants in Algeria

Due to premature defoliation, early blight epidemics can cause major yield losses. Large-spore Alternaria species such as A. solani and A. tomatophila have long been recognized as important pathogens responsible for such blight disease in the family Solanaceae and thus represent a serious risk for crop production. Small-spore Alternaria species have also been frequently isolated from plant samples with typical blight symptoms but their incidence as primary pathogens is often controversial. In order to study the diversity of small-spore Alternaria species, 32 isolates were selected from a larger collection of 130 isolates from infected leaves, fruits and stems of tomato from various growing regions of North-West Algeria. Morphological characterization under standard conditions and polymerase chain reaction (PCR) analyses using specific primers to amplify a part of the ITS regions and the 5.8S gene were conducted to confirm their identification as members of the alternata section. They were then examined according to morphological characteristics of conidia and sporulation patterns on potato carrot agar (PCA) and were segregated into three morphological species: A. alternata, A. tenuissima and A. arborescens. Colony type, substrate colour, margin, zonation, pigmentation, colony diameter and conidia production were studied on potato sucrose agar (PSA). Physiological parameters and nutritional requirements of the isolates were also assessed and a data matrix based on cluster analysis and Euclidean distance was constructed. Results of pathogenicity test on tomato showed obvious diversity among the isolates and they could be separated into two groups based on their virulence. The dendrogram based on the influence of cultural, nutritional and physiological characters suggests moderate heterogeneity within the populations of A. alternata and A. tenuissima. The small-spore species formed five clusters that fundamentally paralleled the morphological groupings. However, the results provided no evidence for geographical and pathogenicity clustering of isolates

First report of tomato early blight caused by Alternaria grandis in Algeria

Tomatoes (Solanum lycopersicum) are widely cultivated in Algeria throughout the year. In northwestern growing areas, characterized by temperate humid climates, severe early blight symptoms (i.e., black lesions surrounded by a yellow halo) on tomato leaves are regularly observed. In 2013, diseased samples were collected from various cultivars in five farms of the Mostaganem region where average disease incidence reached 50%. Plant material was cut into ∼2-mm pieces, surface sterilized in 0.1% (v/v) Na hypochlorite for 2 min, transferred into potato agar medium, and incubated for 48 h at 25°C. Fungal mycelium developing from the lesion margins was transferred to potato carrot agar medium and further incubated for 7 days alternating darkness and cool-white fluorescent light to induce sporulation. Both small- and large-spored Alternaria isolates were obtained. While most of the large-spored isolates had morphological characteristics of A. linariae (syn. A. tomatophila) (Woudenberg et al. 2014), large-spored isolates from one location (Mamache) produced ovoid conidia whose length and width were 149.8 ± 8.9 µm and 16.4 ± 1.3 µm, respectively, ended by a single beak measuring up to 120 µm. Based on these morphological characteristics and host origin, these isolates were initially described as A. solani (Simmons 2000). To confirm the identification at the species level, DNA was extracted from mycelium of four representative isolates. As polymorphism in the ITS regions of rDNA is too low to delineate species within the Alternaria section Porri (Woudenberg et al. 2014), partial regions of the glyceraldehyde-3-phosphate dehydrogenase (gpd) and of the calmodulin (cal) genes were amplified using published primer sets (Gannibal et al. 2014; Woudenberg et al. 2014). For two isolates (NB250 and NB252), the sequences of the amplified products (GenBank Accession Nos. KR911747, KR911752 KR911765, and KR911767) were 100% identical to corresponding sequences of A. solani isolate CBS 109157 (GQ180080 and KJ397981). The gpd and cal sequences of the remaining isolates (NB248 and NB249, GenBank Accession Nos. KR911748, KR911754, KR911763, and KR911764) shared 100% sequence homology to A. grandis isolate CBS109158 (JQ646341 and JQ646249) and they were therefore assigned to this species. To confirm pathogenicity on tomato, the four isolates were spray inoculated (104 conidia/ml) on leaves of 3-week-old tomato plants (cv. Saint Pierre) in the greenhouse. Three replicates were performed for each test. Plants were rated for disease symptoms up to 21 days post inoculation (dpi). No symptom was observed on control plants treated with distilled water. All plants inoculated with A. solani and A. grandis isolates produced extending lesions on leaves albeit with variable virulence (affected leaf area from 50 to 80% at 21 dpi for NB249 and NB250, respectively). To our knowledge, this is the first report of A. grandis infecting tomato in Algeria and in Africa. Moreover, A. grandis has been reported on potato crops in North and South America (Simmons 2000; Rodrigues et al. 2010), but never on tomato. The fact that potato and tomato fields often coexist in close proximity in northwestern Algeria even with farmers using potato in rotation with tomato may favor the development of A. grandis on the latter plant species

Alternaria species associated with early blight epidemics on tomato and other Solanaceae crops in northwestern Algeria

Early blight is a common disease of Solanaceae crops worldwide. The occurrence of Alternaria spp. was studied during three epidemics on tomato in northwestern Algeria. Alternaria was detected in more than 80 % of the diseased plant samples and accounted for more than 50 % of the total fungal isolates recovered from these samples. Morphological and molecular investigations revealed that small-spored isolates producing beaked conidia, i.e. belonging to the section alternaria, were prominent in most of the surveyed locations representing more than 80 % of the total Alternaria isolates in three locations (Mascara, Ain Témouchent and Sidi Belabbèsse). Based on their sporulation patterns they were recognized as A. alternata and A. tenuissima. Small-spored isolates producing conidia without beak and assigned to A. consortialis were also found at a low frequency (< 1 %). Large-spored isolates producing conidia ended by typical long beaks and identified as A. linariae (syn. A. tomatophila), A. solani and A. grandis were also recovered from all the sampled areas and represented 33.8 %, 6.3 % and 1.3 % of the total Alternaria isolates, respectively. Pathogenicity tests on tomato with a selection of 85 strains representative of the isolates collection revealed that all the tested isolates were able to produce extending lesions on inoculated leaves albeit with variable intensity. Large-spored species included the most aggressive isolates. Small-spored Alternaria, although less aggressive than large-spored Alternaria, had the ability to provoke brown necrotic spots and circumstantially developed synergistic interactions in mixed infections with moderately aggressive isolates of A. linariae

NMR evidence of silicate and carbonate competition for cations in solution at low temperature: Case of Ca2+, Zn2+, Pb2+, and Al3+

The characterization of solids obtained by mixing soluble silicates and carbonates with metal salts containing cations such as Zn2+, Pb2+, Ca2+, or Al3+ has been performed. X-ray diffraction, scanning electron microscopy, and high-resolution Si-29 and Al-27 NMR of these solids have been carried out. Pb and Ca form crystallized carbonate precipitates and amorphous silicates. Al and Zn form only amorphous silicates. The speciation of the different complexes formed is achieved by decomposition of the Si-29 NMR spectra. It is then possible to explain the reaction mechanisms occurring between the soluble silicates and the cations. In no case is there any silica formed in the precipitate (no Q(4) entity). The most reactive silicate species present in the samples are formed by Q(3) units