Azolla sporulation in response to application of some selected auxins and their combination with gibberellic acid

Abstract

Application of indoleacetic acid (IAA) at a concentration of 2–10 µg ml–1 significantly enhanced the sporulation frequency and number of microsporocarps per plant in Azolla microphylla (two strains), Azolla caroliniana and Azolla pinnata. An increase in the number of megasporocarps was observed in A. microphylla at 4 µg ml–1 and 6 µg ml–1 and in A. caroliniana and A. pinnata at all the concentrations. The optimal IAA concentration for the sporulation of the three Azolla species was 6 µg ml–1. Application of IAA at this level increased the sporulation frequency and number of total sporocarps per plant by 39.3–99.5% and 56.9–91.1% over the control, respectively. The increase in the number of megasporocarps was more than that of the microsporocarps. In view of an almost similar response of different Azolla species to IAA, only the two A. microphylla strains with year-round sporulation were used in the subsequent investigations. In these strains, application of napthaleneacetic acid (NAA) and indolebutyric acid (IBA) at a concentration of 2–10 µg ml–1 also increased the sporulation frequency and sporocarp number significantly and the optimal concentration was 6 µg ml–1. Gibberellic acid (GA3; 2.5 µg ml–1) was more effective than IAA, NAA and IBA (6 µg ml–1) for enhancing the sporulation frequency and microsporocarp number but not the megasporocarp number. Application of one of the auxins plus GA3 had some synergistic effects and led to the formation of more megasporocarps, while maintaining the sporulation frequency and microsporocarp number to the level of the treatment with GA3 alone. This practice could be advantageous for the production of Azolla sporocarps because it is the megasporocarps that generate new plants after fertilization and germination.