Molecular identification, in vitro copper resistance and antibiotics susceptibility of the causal agent of the olive knot disease in Morocco

Aims@#This study aimed to i) identify Pseudomonas savastanoi pv. savastanoi (Pss) as a causal agent of the olive knot on the basis of biochemical, pathogenicity and PCR technique ii) investigate in vitro bacterial resistance toward copper-based compounds and efficiency of some antibiotics on pathogen suppression. @*Methodology and results@#Biochemical, pathogenicity and molecular identification based on alkaline method for the DNA extraction were performed to identify possible causal agent of the olive knot. Copper resistance for Pss strains was evaluated by inoculation of bacterial suspensions into YPG medium, containing the cupric sulfate at 0, 100, 250 and 500 ppm. The efficiency of eight antibiotics on Pss strain was evaluated at different concentrations. Fifty-nine isolates caused typical knots at the site of inoculation with bacterial suspensions. All isolates have been identified as Pss using specific primers. No resistance to copper was detected with concentration of 500 ppm. In contrast, copper resistance was found during 48 h with lower concentration (100 or 250 ppm). The maximal inhibition of Pss 2102-4M was observed with the highest concentration (20 μg/mL) of the Aureomycin, Streptomycin and Novobiocin with inhibition diameters of 30, 24 and 10 mm, respectively. Whereas, Colchicine, Bacitracin, Cephalex, Ampicillin and Cycloserine have no inhibitory effect on the Pss 2102-4M strain. @*Conclusion, significance and impact of study@#The alkaline method for the DNA extraction from pure culture was reliable and rapid and can be recommended for molecular detection the causal agent of the olive knot. This is the first report determined copper resistance levels of Moroccan strains of Pss and in vitro evaluated for the susceptibility towards the antibiotics.

Study of Arbuscular Mycorrhizal Fungi Diversity and Its Effect on Growth and Development of Leek Plants (Allium porrum L.)

The effect of a composite endomycorrhizal inoculum, native to the rhizosphere of the olive tree, was studied on the growth of leek plants (Allium porrum L.). Inoculation of leek plants was carried out by contacting the root system of leeks with the inoculum endomycorrhizal derived from the olive tree rhizosphere. After five months of inoculation, a significant effect is observed on the growth of the inoculated plants according to witnesses. Indeed, the average values of the aerial weight (11.62 g) and root weight (18.52 g), the diameter (0.5 cm) and the number of leaves (7) of the inoculated plants are higher than those noted in the control plants, respectively 4.42 g, 7.95 g, 0.3 cm, 5.57. Moreover, the frequency and intensity of mycorrhization, respectively 96.66% and 50.33%, the arbuscules contents (44.33%) and vesicles (32.44%) are very important. The roots of control plants are not mycorrhizal. The average number of spores formed in the rhizosphere of the inoculated plants is 160 spores per 100 g of soil. These spores are those of 85 endomycorrhizal species belonging to 16 different genera: Glomus (34 species), Acaulospora (18 species), Gigaspora (5 species), Entrophospora (3 species), Scutellospora (5 species), Pacispora (2 species), Claroideoglomus (2 species), Dentiscutata (1 species), Septoglomus (1 species), Paraglomus (2 species), Rhizoglomus (2 species), Ambispora (3 species), Cetraspora (1 species), Funneliformis (1 species), Diversispora (4 species) and Viscospora (1 species). Statistical analyzes were performed by analysis of variance by the ANOVA test at the 5% level using the STATISTICA software. Leek, is a mycotrophic plant that can be used to multiply an endomycorrhizal inoculum suitable for use in nurseries, and to produce seedlings of different plant species that are vigorous and resistant to pathogens and water stress after transplantation.

Neofusiccocum parvum as Uncommon Fungal Species (or Emerging Pathogen) on Strawberry Plants in Morocco

During a survey on fungi associated with decline symptoms on strawberry plant of Venicia variety, one species belonging to the Botryosphaeriaceae family was isolated. Based on morphological and cultural characteristics, this species identified as Neofusicoccum parvum was reported for the first time in Morocco. To verify the pathogenicity of the fungus, detached leaves of three strawberry varieties were inoculated artificially by depositing over their intact surface mycelia plug or conidial suspension from N. parvum. Severity index was greater on festival leaves reaching 88% compared to 77.73% on Sabrina. In the third treatment, Guariguette showed a low susceptibility with a severity index in order of 25.07%. Conidia concentration on the leaf surface of the Festival and Sabrina strawberry leaves was respectively 1.62 105and 1.2 105 conidia cm-2. Otherwise, in the second treatment, it has been reduced to less than 1.41105 1.16 and 105 conidia.cm-2 on leaves of Festival and Sabrina respectively. After inoculation, the fungus was re-isolated from the lesions to verify Koch’s postulates.

Influence of Variations in Climatic Factors and Some Cultural Practices on Knot Disease Development on Oleaster and Olive Tree (Olea europaea L,) Northwest of Morocco

The present study is conducted to know the effect of certain cultural practices and the variation of temperature and humidity (bioclimatic stage, slope exposure) on the distribution and importance of the development of tuberculosis disease of olive trees, caused by Pseudomonas savastanoi pv. savastanoi(PSS), in Northwest of Morocco. 1584 trees of oleaster and olive trees (cuttings and grafts) were observed during the period 2013-2014 in several groves in the northwest regions of Morocco. The percentage of infection was calculated by the number of olive trees showing the symptoms of tuberculosis caused by Pseudomonas savastanoi pv. savastanoi. The intensity of the disease in the oleaster and the olive tree was determined by counting the number of knots. The prospection was showed that olive plots are more or less attacked by tuberculosis in the northwest part region of Morocco and more apparent in olive trees in development station in Zoumi and in Boukkara (North and West oriented slopes of 68% and 28% respectively). The percentage of infection was very high in oleaster and graft plants (31% and 28% respectively) in two humid stations (Zoumi and Boukkara). The intensity of the tuberculosis disease showed that oleaster trees are most attacked. The development of olive trees is highly influenced by the symptoms in branches. The fruit size and weight were significantly higher in healthy olive trees than in those showing the symptoms of tuberculosis.

Follow-up of a Composite Endomycorrhizal Inoculum in the Rhizosphere of Olive Plants, Analysis after 42 Months of Culture

Endomycorrhizal inoculum, consisting of more than 26 mycorrhizal species, has been followed over time at the rhizosphere of olive trees. The evolution during time of this endomycorrhizal inoculum at the rhizosphere of plants has been discussed in this study. After 42 months, 45 species were isolated from the rhizosphere of inoculated olive plants. These species belong to 6 genera (Glomus, Acaulospora, Gigaspora; Scutellospora; Pacispora and Entrophospora), from these genera, Glomus was the most dominant (40%) followed by the Acaulospora (30%). Glomus constrictum and G. intraradices were the most abundant species, their frequency are respectively 17% and 15%. In comparison between detected species, those of primary inoculum and those recovered after 30 months, 36 endomycorrhizal species appeared and 14 species disappeared, but four species G. clarum, G. intraradices, G. mossea and G. versiforme have been able to maintain their status and stability of multiplication in the rhizosphere of olive plants.