Arthrobacter sp. Inoculation Improves Cactus Pear Growth, Quality of Fruits, and Nutraceutical Properties of Cladodes.

A study was undertaken to determine the effects of a strain of Arthrobacter sp., a Plant Growth-Promoting Bacteria (PGPB), on plant phenology and qualitative composition of Opuntia ficus-indica (L.) Mill. fruits and cladodes. The strain was inoculated in soil, and its effects on cactus pear plants were detected and compared to nontreated plants. Compared to the latter, the treatment with bacteria promoted an earlier plant sprouting (2 months before the control) and fruitification, ameliorating fruit quality (i.e., improved fresh and dry weight: + 24% and + 26%, respectively, increased total solid content by 30% and polyphenols concentrations by 22%). The quality and quantity of monosaccharides of cladodes were also increased by Arthrobacter sp. with a positive effect on their nutraceutical value. In summer, the mean values of xylose, arabinose, and mannose were significantly higher in treated compared to not treated plants (+ 3.54; + 7.04; + 4.76 mg/kg d.w. respectively). A similar trend was observed in autumn, when the cladodes of inoculated plants had higher contents, i.e., 33% xylose, 65% arabinose, and 40% mannose, respect to the controls. In conclusion, Arthrobacter sp. plays a role in the improvement of nutritional and nutraceutical properties of cactus pear plants due to its capabilities to promote plant growth. Therefore, these results open new perspectives in PGPB application in the agro-farming system as alternative strategy to improve cactus pear growth, yield, and cladodes quality, being the latter the main by-product to be utilized for additional industrial uses.

Evaluation of the fern Azolla for growth, nitrogen and phosphorus removal from wastewater.

Water fern (Azolla filiculoides Lam.) has been assessed for nitrogen and phosphorus removal in outdoor experiments comparing sewage water (S) from an experimental aquaculture plant, well water (W) and mineral growth medium Hoagland (H). The experiments were undertaken during the spring and the summer. The yield of fern biomass and nitrogenase activity was higher in H than in W and S waters. The enzyme activity had a decreasing trend with significant differences (p < 0.05) in the three waters. Peroxidase (POD) activity in April decreased with significative differences in W and S waters (p < 0.05). The electrical conductivity and the concentrations of NO3- in the three waters decreased significantly (p < 0.05). The highest removal of nitrate from the media was obtained in July. In S water, NO2- concentration decreased, while it increased in W water. PO(4)3- concentration was very low in W and S waters and decreased in H medium. The results obtained confirm the ability of the fern to grow in sewage water.