Effects of heavy metals on seedlings germination and growth in different cardoon genotypes

Cardoon (Cynara cardunculus L.) is a perennial crop, particularly adapted to the Mediterranean environment with a very intensive growth in autumn and winter and seed ripening in summer. The crop is able to accumulate heavy metals from polluted soils and thus it seems to tolerate this stress. Up to now, there are no studies on seed germination and emergence of cardoon seedlings under heavy metal stresses. For this reason, the aim of this study was to evaluate the possibility to use cardoon for the phytoremediation of metal-contaminated soils. Thus three cardoon accessions, two wild populations and one domestic cardoon, were compared in order to evaluate the germination and seedling emergence under cadmium (Cd) and arsenic (As) stresses. The experiments were conducted using a completely randomized block design with five replications and four different concentrations of Cd and As (10, 50, 100 and 200 µM) and Cd+As (10+10, 50+50, 100+100 and 200+200 µM). The seeds were incubated in Agar medium supplemented with Cd and As standard solutions under controlled environmental conditions, in a growth chamber 12/12 h light/dark cycle at 25/15°C. The agar medium allowed to evaluate the heavy metal effects on seed germination and seedlings growth. The percentage of seeds germination, under Cd or Cd+As stresses was similar to the control under no heavy metals (80-90%). Instead, germination percentage decreased with the increasing of As concentration in the medium (80% at 10 and 50 µM; 60% at 100 µM; 30% at 200 µM). We also report that high concentrations of As, even in combination with Cd, stopped the radicle emergence from the germinated seed. At low concentration of As and for all concentrations of Cd we observed a reduction of the seedling growth from 20% in low concentration of Cd (10 and 50 µM) to 50% in high concentration of Cd (100-200 µM) and low concentration of As and Cd+As. These results showed that the three cardoon genotypes have a good tolerance to Cd; while the As tolerance is higher when combined with Cd.