© 2007 Heron Publishing—Victoria, Canada
Girdling effects on fruit set and quantum yield efficiency of PSII in two Citrus cultivars
F. Rivas (1), A. Gravina (2) and M. Agustí (1, 3)
1. Instituto Agroforestal Mediterráneo, Universidad Politécnica de Valencia. Camino de Vera s/n. E-46022. Valencia, Spain / 2. Departamento de Producción Vegetal, Ecofisiología de Citrus, Universidad de la República, Facultad de Agronomía. Garzón 780.
C.P: 12900. Montevideo, Uruguay / 3. Corresponding author (magusti@prv.upv.es) / Received March 14, 2006; accepted May 19, 2006; published online January 2, 2007
Summary
Girdling effects on fruitlet abscission, leaf chlorophyll, chlorophyll a fluorescence and carbohydrate concentration in various
flowering and vegetative shoots were studied during natural fruit drop in two Citrus cultivars. Irrespective of shoot type, girdling delayed fruitlet abscission, but only fruitlets borne on leafy shoots had
increased final fruit set. Chlorophyll a fluorescence analysis revealed differences in quantum yield efficiency of photosystem
II of light adapted leaves (ΦPSII) among shoot types and in response to girdling. In young leaves of vegetative shoots, girdling decreased ΦPSII, whereas ΦPSII increased from Day 30 after girdling in young leaves of leafy flowering shoots; however, ΦPSII did not change in mature leaves during fruit set in either control or girdled trees. Girdling altered leaf carbohydrate concentrations
and the photosynthetic performance of the various shoot types. Our results indicate that, in Citrus, several carbohydrate-based regulatory mechanisms of photosynthesis coexist during carbohydrate accumulation brought about
by girdling. It is concluded that the delay in fruitlet abscission and the increase in ΦPSII observed in girdled leafy flowering shoots are the mechanisms underlying the enhancement of fruit set after girdling.
Keywords:
abscission, carbohydrates, chlorophyll a fluorescence, sink activity, SPAD.
