Foliar sprays of 25–100 mg L−1 dinitrophenol, sodium azide (NaN3) and thiourea solution applied to Azolla microphylla (strains 202 and 203) at seven days after inoculation significantly increased the sporulation frequency and number of micro- and mega-sporocarps per plant. Azolla biomass production was decreased by the application of NaN3 at 50–100 mg L−1 and dinitrophenol or thiourea at 75 and 100 mg L−1. Both the sporulation frequency and sporocarp number were maximal with dinitrophenol and NaN3 at 100 mg L−1 and thiourea at 75 mg L−1. At this concentration, NaN3 was more effective than dinitrophenol and thiourea in enhancing sporulation in A. microphylla (strain 203). The sporulation frequency and micro-sporocarp number were significantly higher with gibberellic acid (2.5 mg L−1) than with indole acetic acid (6 mg L−1) application, while the effects of NaN3 were comparable with those of gibberellic acid. The mega-sporocarp numbers in these treatments were comparable. The combined application of any two of the metabolic inhibitors had antagonistic effects and decreased the sporulation frequency and sporocarp number over their individual applications. Combined applications also substantially reduced the biomass production. The application of gibberellic acid or indole acetic acid along with one of the metabolic inhibitors had synergistic effects on the formation of sporocarps and significantly increased the biomass production, irrespective of the metabolic inhibitor treatment. The number of both micro- and mega-sporocarps in the gibberellic acid + NaN3 and indole acetic acid + NaN3 treatments, and micro-sporocarps in the gibberellic acid + dinitrophenol, indole acetic acid + dinitrophenol and indole acetic acid + thiourea treatments was significantly higher than when each of these chemicals was applied alone. Of the different combinations of gibberellic acid, indole acetic acid and NaN3, gibberellic acid + NaN3 recorded the highest sporulation frequency and micro-sporocarp number, and indole acetic acid + NaN3 the highest mega-sporocarp number. Application of all three chemicals together had no extra advantage.
