Acaricidal effects of cardiac glycosides, azadirachtin and neem oil against the camel tick, Hyalomma dromedarii (Acari: Ixodidae)

The cardiac glycoside, digitoxin, from Digitalis purpurea L (Scrophulariaceae), a cardiac glycosidal (cardenolide) extract from Calotropis procera (Ait) R Br (Asclepiadaceae), azadirachtin and neem oil from Azadirachta indica A Juss (Meliaceae) were tested for their effects against larvae and adult stages of the camel tick, Hyalomma dromedarii Koch (Acari: Ixodidae). The contact LC50 values of the first three materials against adults were 4.08, 9.63 and >40.7 microg cm(-2), respectively, whereas the dipping LC50 values of the four materials were 409.9, 1096, >5000 and >5000 mg litre(-1), respectively. Contact and dipping LC50 values of the extract and azadirachtin against larvae were 6.16, >20.3 microg cm(-2) and 587.7 and >2500 mg litre(-1), respectively. Azadirachtin had no effects on egg production or feeding of adults up to 5000 mg litre(-1); however at 2500 mg litre(-1), it caused significant reduction in feeding activity of larve, prolonged the period for moulting to nymphal stage, and caused 60% reduction in moultability. Results of the two cardiac glycoside materials are comparable with those of several commercial acaricides. The risks and benefits associated with the use of cardiac glycosides are considered.     

Variants of Digitalis obscura from irradiated shoot tips

Shoot tips excised from genotype T4 of Digitalis obscura were exposed to gamma rays (20–100 Gy). Radiosensitivity was assessed and LD₅₀ determined was about 60 Gy. The effect of the herbicide amitrole on shoot-tip culture was investigated, efficient bleaching was obtained with 10 mg/l amitrole. Shoot tips mutagenized (20–40 Gy) were cultured on several selective amitrole-containing media, but none of them permitted prolonged survival of the green shoots formed. Ploidy level of the plantlets developed was analysed by flow cytometry 8 and 18 months after culture establishment. Variations detected corresponded to aneuploid changes and increased in parallel with the gamma radiation dose. Plantlets developed from irradiated shoot tips presented a high variability in their cardenolide production (878 to 3291 μg/g d.w.), including variants with similar or even higher productivities than the native T4 plant. This revised version was published online in August 2006 with corrections to the Cover Date.     

Relationships among soil characteristics,plant macronutrients,and cardenolide accumulation in natural populations of Digitalis obscura

In the present study, we have investigated relationships among several soil parameters (pH, organic matter, total carbonate, macronutrients, electrical conductivity, cation‐exchange capacity) and macronutrient and cardenolide contents in leaves of wild Digitalis obscura plants. Young and mature leaves and soil samples were collected in ten different areas, corresponding to three Mediterranean bioclimatic belts (thermo‐, meso‐, and supramediterranean belts). Soil and leaf macronutrient (N, P, K, Ca, and Mg) contents and leaf cardenolide contents were determined. Bioclimatic conditions influenced the development of D. obscura, biomass being lowest in plant populations of the supramediterranean belt, but they did not exert any relevant effect on the contents of macronutrients in soils and plants. Magnesium (total and EDTA‐extracted) was the only soil macronutrient significantly correlated with its content in the plant. Cardenolide contents were negatively correlated with the N, P, and K contents in young leaves, whereas such correlations were highly significant and positive for Mg.     

Soil‐plant relationships,micronutrient contents,and cardenolide production in natural populations of Digitalis obscura

The production of secondary metabolites by plants growing in natural populations is conditioned by environmental factors. In the present study, we have investigated the relationships among soil properties, micronutrients in soils and plants, and cardenolide production from wild Digitalis obscura (Scrophulariaceae) populations. Young and mature leaves and soil samples were collected in ten different populations, corresponding to three Mediterranean bioclimatic belts (Thermo‐, Meso‐, and Supramediterranean belts). Soil (total and EDTA‐extractable) and leaf micronutrients (Fe, Mn, Zn, and Cu), and leaf cardenolide accumulation have been determined. Significant negative correlations were observed between Fe, Mn or Zn concentration in leaves and soil pH, as well as between Fe or Mn in leaves and carbonate content of soils. Only EDTA‐extractable Mn was significantly correlated with Mn content in the plants. With regard to cardenolide content in leaves, this parameter was negatively correlated with Zn_leaf in young leaves and with Mn_leaf in old leaves. Positively correlated, however, were Fe and cardenolide content in young leaves. The influence of environmental conditions and leaf micronutrient contents on cardenolide accumulation is discussed.