Gibberellic acid sprays, girdling, flower thinning and potassium applications affect fruit splitting and yield in the ‘Ellendale’ tangor

The anatomy of the fruit in relation to the propensity of citrus species to split

“…Contrary to what could be expected from its effect on fruit shape, GA3 failed to decrease splitting, which was increased to the same extent as fruit set (Table 5). This effect of GA3 con®rms previous reports showing an increase in splitting, both in absolute and relative terms, by GA3 applications at ¯owering in Nova (Goren et al, 1992;Almela et al, 1994;García-Luis et al, 1994) and Ellendale (Rabe and Van Rensburg, 1996). In addition to the effect on fruit shape, 2,4-D markedly increased the growth of the navel, a factor which increases splitting (Table 3; Lima and Davies, 1984;García-Luis et al, 1994).…”

“…In some cases, however, the number of fruits affected is exceedingly high, a situation reported for several cultivars of navel oranges such as Washington (Erickson, 1968;Lima and Davies, 1984), Navelina (De Cicco et al, 1988;Ruiz and Primo-Millo, 1989), and Skaggs Bonanza (Monselise et al, 1986) in Valencia orange (Bar-Akiva, 1975), and particularly in several mandarin hybrids such as Murcott, Ellendale, Nova and Niva (Monselise et al, 1986;Ruiz and Primo-Millo, 1989;Goldschmidt et al, 1992;Goren et al, 1992;Almela et al, 1994;García-Luis et al, 1994;Rabe and Van Rensburg, 1996;Barry and Bower, 1997). In these hybrids, the losses caused by this alteration may represent up to 50% of the potential yield, making it uneconomical to grow these cultivars in some climatic areas.…”

“…Con¯icting reports are found in the literature on the effectiveness of several cultural practices. The application of potassium and calcium has been reported to reduce splitting (Monselise et al, 1986;De Cicco et al, 1988;Ruiz and Primo-Millo, 1989;Almela et al, 1994), to have no consistent effect (García-Luis et al, 1994;Barry and Bower, 1997), or to increase it (Rabe and Van Rensburg, 1996). The same variability is found in the response to 2,4-D sprays, which have been reported to reduce (Monselise et al, 1986;Almela et al, 1994) or to have no consistent effect on splitting (Goren et al, 1992;Barry and Bower, 1997).…”

“…A climate effect seems likely, as splitting is most prevalent in humid and warm climates (Alexander, 1983;Saunt, 1990), but the reason of this effect has not been ascertained. Splitting has been shown to decrease under reduced water supply (Goldschmidt et al, 1992;Goren et al, 1992), to be inversely related to water availability (De Cicco et al, 1988) or as being unrelated to rainfall (Rabe and Van Rensburg, 1996). On the other hand, treatments aiming to increase fruit set, either girdling or GA3 sprays at full bloom, have been reported invariably to increase splitting both in absolute and in relative terms (Goren et al, 1992;García-Luis et al, 1994;Rabe and Van Rensburg, 1996;Barry and Bower, 1997).…”

“…García-Luis et al (1994) reported that splitting in Nova is related to the presence of an open stylar end in the fruit and a navel. Rabe and Van Rensburg (1996) stated that the potential for fruit splitting in Ellendale tangor is determined during the early stages of fruit development, but the cause of it was not ascertained. In the present report, the anatomical characteristics of the ovaries and fruitlets of cultivars prone to splitting, and those of cultivars which usually do not split, have been compared.…”