The co-cultivation of Azolla filiculoides and Oryza sativa shape the phenotype of rice plants

Climate change and rising world population are challenging us to pursue alternative routes to increase food availability in a sustainable way. A huge step forward in this sense would be the increment of the production, while decreasing the ecological impact, of cereals, as they are the major staple food worldwide. An example of sustainable production of cereals comes from the Far East where rice has been co-cultivated with ferns belonging to the genus Azolla for many centuries to increase its productivity. Ferns belonging to this genus in fact by establishing a symbiosis with the nitrogen fixing Trichormus azollae (Komarek and Anagnostidis 1989), a cyanobacteria release nitrogen to the rice paddies to that rice productivity can increase by more than 50%. Moving from these considerations, here we co-cultivated rice (Oriza sativa ssp. japonica cv. Kitaake) with Azolla filiculoides to assess both qualitatively and quantitatively the effects of this interaction on rice phenotypic traits. The experiments were carried out in a growth chamber, in hydroponic condition using as control rice cultivated alone. During 60 days we measured morphological features such as leaf number and height, tillers number, ligule height in both co-cultivated rice and in control plants. The amount of aerenchyma spaces in sheaths was also measured. Regarding roots, we measured fresh and dry weight, number and length of adventitious roots at 15, 30 and 60 days of co-cultivation. Data suggest that A. filiculoides promotes the growth of both the submerged and emerged rice organs and structures investigated. However, the increase is different in aerial organs compared to roots, as the decrease of the root/shoot ratio suggests that the carbon partitioning is higher in the aerial organs. Moreover, since through the interaction with hormones, reactive oxygen species and calcium nitric oxide (NO) plays a fundamental role in plant stress adaptation, senescence and growth, experiments are in progress to assess whether NO exerts a pivotal role in root development in both rice co- cultivated and control plants. Likewise, studies are ongoing to shed light into the interplay between NO and auxine, the hormone underlying rooting differentiation.