Uncovering morphological and physiological markers to distinguish Azolla strains

Abstract

Taxonomy of Azolla was extensively studied, but still its identification based on morphological, physiological, and reproductive structure remains unclear. Hence, an attempt was made to differentiate Azolla strains based on morphological and physiological traits, keeping six known Azolla (Azolla microphylla, Azolla caroliniana, Azolla mexicana, Azolla rubra, Azolla filiculoides, and Azolla pinnata) as reference for this study. The results showed that out of 96, 21 strains were sporulated during December, 2017 to February 2018 along with two known species, i.e., A. microphylla and A. pinnata. All sporulating strains (except GSMI 1) showed morphological-resemblance with A. pinnata, whereas GSMI 1 was resembled with A. microphylla. Biplot principal coordinate analysis (PCoA) based on physiological data revealed that GSMI 1 was significantly resembled with A. microphylla. Moreover, the presence of rounded dorsal leaf lobe in A. caroliniana has made it unique in Euzolla sub-section and hence, differentiated from other four species (A. microphylla, A. mexicana, A. rubra, and A. filiculoides). WinRHIZO-based root-imaging technique showed the presence of thick root hairs in A. pinnata as compared to other Azolla strains, whereas efficiency of photosystem II (Fv /Fm, a chlorophyll fluorescence-imaging derived value) and relative growth rate were found higher in CRRI 4. In conclusion, the present study generated a presumptive classification key of 102 strains of Azolla for the first time, which indicates clearly that taxonomy in Azolla should be reviewed. Validation of these characters through molecular markers will give further insight about their classification.