Aspects of fruit size and quality in citrus

[摘要] ENGLISH ABSTRACT: Fruit size can be a problem in 'Clementine' mandarin and 'Valencia' orange in the WesternCape region of South Africa. Small fruit is not only unacceptable to the consumer but is alsomore difficult and expensive to harvest. Means of alleviating this problem is to manage thecrop load. Hand thinning trials were conducted to evaluate the effect of timing and severitythereof in enhancing fruit size. The benefits of enhancing large fruit size was obtained by aheavy-thinning (60% fruitlet removed) treatment, but the actual benefits were offset by areduction of total yield. Yield was reduced up to 30% when heavy thinning treatments wereapplied. No effect on early or late treatments were obtained since the trial was conductedrather late (4 to 6 weeks after the physiological fruit drop period) to obtain the desirableresults. However, better packouts are expected with thinning treatments since blemished fruitare also removed.The effect of multiple 2,4-dichlorophenoxy propionic acid (dichlorprop) sprays were alsoevaluated on 'Nules Clemetine' mandarin. Comparing multiple sprays with a single spray, itwas observed that more than one spray was no better in improving fruit size. The use ofmultiple dichlorprop sprays resulted in no additional yield reduction, while internal fruitquality was also not affected. The best results were obtained with dichlorprop at 50 mg. L-1•The use of dichlorprop with different surfactants was evaluated in both 'Clementine'mandarin and 'Valencia' orange. The fruit size was increased from 50 mg. L-1 up to 100 mg.L-1• Yield was usually not affected but, where reductions were experienced, yield of largefruit (>55 mm) was not significantly affected. In the 'Valencia' orange trials, during the firstyear, dichlorprop was sprayed relatively late (fruit diameter: 19 mm). No fruit size, yield andinternal fruit quality effects were observed. The following year, when early and late sprays (fruit diameter at spray time = 8 and 12 mm, respectively) were evaluated, it was observedthat late sprays had no effect on fruit size, whereas fruit size (48 fruit per carton) wassignificantly increased by early sprays. This implies that the dichlorprop effect on fruit sizeis during the early stages of fruit development, just after or during the late stage of thephysiological fruit drop period. Yield was drastically reduced by up to 35%, which affectedthe actual kilograms of large fruit adversely in some treatments. Juice percentage wasinconsistent and tended to be reduced by dichlorprop application. Dichlorprop tended toincrease TSS slightly in year one and significantly so in year two, but did not affect theTSS:TA ratio. The use of Orchex mineral oils as surfactant at 150 mL. 100 L-1 was effectiveand seemingly allowed lower rates of dichlorprop to be used. Therefore, surfactants seemedto show potential in enhancing dichlorprop efficiency to reduce the application cost.The dichlorprop-sprayed fruit was used to measure carotenoid content of the rind during thelater stage of fruit development. Observations indicate that dichlorprop-sprayed fruit at 50mg. L-1 obtained better carotenoid content in both 'Clementines' mandarin and 'Valencia'orange. Also, fruit exposed to light had higher carotenoid levels as compared to fruit shadedwith brown paper bags. However, dichlorprop-sprayed fruit at 100 mg. L-1, even thoughexposed to light did not show significant differences with unsprayed in both shaded andexposed conditions. Therefore, no consistent effect of dichlorprop was established on totalcarotenoid content of the rind.

[发布机构] Stellenbosch University