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The flowering of carambola (averrhoa carambola l) is more strongly influenced by water stress than by photoperiod and diurnal temperature variation

S. Salakpetch, D.W. Turner and B. Dell

Chantaburi Horticultural Research Centre, Department of Agriculture, Chantaburi, 22190, Thailand;
School of Agriculture, University of Western Australia, Nedlands, W.A. 6009;
School of Biological and Environmental Sciences, Murdoch University, Murdoch, W.A. 6150

Carambola is probably of Indo-Malayan origin and is cultivated pantropically(1). Its fresh fruit has potential in Australian and overseas markets. Although there are no reports of flowering problems with carambola it is useful to explore factors which contribute to flowering, so that we may be able to manage it.

Temperature, photoperiod and water stress are significant factors in the flowering of many fruit plants such as lychee, grapevines, citrus, pineapple and custard apple(2). This study describes the effects of temperature, photoperiod and water stress on flowering in carambola under controlled conditions.

Methods

Containerised carambola trees two years old were exposed to day/night temperature regimes of 30/25C, 25/20C, 20/15C, 30/15C and 34/20C for 15 days and flowering assessed two months later. The cultivars Thai Knight and Fwang Tung were studied. In a subsequent experiment plants were exposed to 8,12, 14 (standard) and 16 hour photoperiods for 15 days and flowering assessed. Thai Knight plants were exposed to cyclical or continuous water stress for 3 to 4 weeks. Midday leaf water potentials dropped to -2.0 MPa in these treatments.

Results and discussion

Neither fluctuating day/night temperatures or photoperiods (over the range tested) influenced inflorescence production in carambola, except for the 16 hour photoperiod which reduced flowering in cv Thai Knight. Photoperiods of 8 and 12 hours increased the number of flowers per inflorescence by 8-20% compared with the standard (14 Hour) photoperiod. Under long (16 h) photoperiods the trees produced seven times more vegetative shoots per branch.

Fwang Tung consistently had a greater proportion of floral buds per branch, number of inflorescences per branch and number of flowers per inflorescence than Thai Knight under all experimental conditions.

Both cyclical and continuous water stress inhibited flowering in Thai Knight carambola by 75%. Flowering in carambola appears to be only weakly influenced by external environmental conditions but strongly by water stress.

1. Veldkamp, J.F.(1986). In Flora Malesiana. Series 1, 7: 151-178.

2. Haleng, A.H. (1987). In Manipulation of Flowering. Butterworths. pp. 363-378.

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