Ethylene regulation under different watering conditions and its possible involvement in coffee (Coffea arabica L.) flowering

Abstract

Coffee is one of the world's favourite beverage and the second most traded commodity after oil However, coffee quality can be greatly affected by fruit ripening stage at harvest time, which is often asynchronous due to the sequential flowering in this species. Coffee sequential flowering is a result of asynchronies in bud development and also environmental factors, since anthesis is triggered by precipitation after a period of water deficit. This series of events is commonly associated with an increase in ethylene production levels, suggesting that ethylene may be involved in the control of coffee anthesis promotion and its regulation might help to reduce the number of flowering events and thus promoting blossoming concentration. Thus, it was hypothesised that a droughtrewatering-induced ethylene burst might be the basis of the drought-rewateringinduced flowering in coffee trees. In order to test this hypothesis, this study aimed to access the effects of exogenous 1-MCP application on flowering of coffee trees under field conditions and, under greenhouse conditions, we aimed to study the ethylene regulation, through quantification of ethylene levels and expression levels of genes of the ethylene biosynthesis and signaling pathways, in coffee plants under well-watered and water-deficit conditions, as well as, after plant rehydration and 1-MCP treatment.1 -MCP exogenous application, at the concentrations of 50 and 100 mg of a.i. per litre and with spray volume of one litre per plant, was able to promote coffee anthesis in trees of the cultivar ‘Acaiá Cerrado' under field conditions. Ethylene production rates in coffee seedlings from two cultivars, ‘Bourbon Amarelo' and ‘Obatã Vermelho’, growth under greenhouse conditions, were similar under well-watered and water-deficit conditions. Plant rehydration and 1-MCP treatment did not change ethylene release rates from both cultivars when compared to plants under well-watered and water-deficit conditions. However, the analysis of the ethylene regulation, through gene expression analysis, shortly after plant rehydration and 1-MCP treatment, suggest that increased levels may occur, helping to explain anthesis promotion upon 1-MCP application, and supporting the hypothesis that a drought-rewatering-induced ethylene burst might be the basis of the droughtrewatering-induced flowering in coffee trees.