**5. Conclusions**

The outcome of this experiment shows that As uptake and translocation into melon plants were both influenced by its concentration in the nutrient solution and by the genetic background of the rootstock. All tested plants, when grown in an As-enriched solution, showed a high As mobility in the substrate–plant continuum, resulting As accumulators most of all in root and shoot. Intraand interspecific rootstocks differently influenced the Asroot accumulation inside the plant, with the interspecific hybrids proving a superior ability to limit the metalloid entrance into the roots. When subjected to As stress, melon plants acted to limit the metalloid translocation from root to shoot and pulp, so indicating the triggering of physiological mechanisms aimed at limiting the As diffusion inside the plant. To this end, the intraspecific rootstocks displayed a better ability to retain the toxic metalloid into the root system, most of all in an organic form. This feature suggests a higher efficiency of the root chelation mechanisms of As, occurring, in turn, at the expenses of the photosynthetic balance. The interspecific *C. maxima* × *C. moschata* rootstocks gave the best results in terms of fruit biomass under conditions of As stress, so suggesting the possibility to exploit their superior bio-agronomical potential with the aim to improve melon performances in heavily As-polluted areas. "RS841" proved to be the best rootstock in the view of maximizing yield and minimizing, at the same time, the As concentration into the fruit. Thus, the significant differences we found suggest the possibility to deepen this area of research, with the aim of identifying rootstocks genotypes for their superior agronomic and toxicological response to high As contamination in the root zone.

**Author Contributions:** C.L. and S.R.S. conceived the experiments and proposed the experimental design. F.G. and R.P.M. carried out the experiments. R.M. and E.A. carried out chemical experiments. R.P.M., A.E., S.R.S., R.M. interpreted data and wrote the manuscript. F.G. and A.I. critically revised the manuscript.

**Funding:** The research activity was co-funded by the Italian Ministry of University and Research (PRIN project "Health of agroecosystems: chemical, biochemical and biological processes that regulate the mobility of As in the soil-water-plant compartments" code 2010JBNLJ7\_006).

**Conflicts of Interest:** The authors declare no conflict of interest. The funder had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
