Analysis of exogenous auxin and cytokinin action in overcoming root restriction in green and variegated Benjamin fig

Abstract

Green and variegated Benjamin fig (Ficus benjamina) often suffer from root restriction when grown in pots. While exogenous cytokinin applications have proven effective in reversing this stress, the possibility that exogenous auxins, either alone or in combination with cytokinin, may also be helpful has received little attention. In this work, we analyse the response of green and variegated Ficus benjamina rooted cuttings growing in small pots to exogenous supply of auxin and cytokinin at different concentrations, either in single or combined applications. Our results show that both benzyl aminopurine (BAP) and indole acetic acid (IAA), at the highest concentration tested (100 mg L-1) increased leaf development and plant biomass accumulation in green and variegated Ficus genotypes. However, exogenous IAA and BAP appeared to elicit differential plant morpho-physiological responses. While BAP tended to enhance leaf appearance more than IAA did, the latter promoted leaf expansion in a steadier manner than BAP, thus resulting in plants with less, but larger, leaves than those treated with cytokinin. Despite these differences in plant architecture, regression analysis suggests that hormonal-induced growth promotion was solely attributable to enhanced carbon assimilation. Rather unexpectedly, IAA promoted net assimilation and photosynthesis rates at least as effectively as cytokinin. Possible mechanisms involved in growth and development promotion by exogenous application of both hormones are discussed. Auxin treatment may help overcome root restriction in Ficus as effectively as cytokinin in terms of growth promotion, although differences in plant architecture may arise as compared with plants sprayed with the latter hormone.