Late-summer topping increases fruit size in Indian River 'murcott' with little reduction in yield

Ed Stover, Scott Ciliento, Travis Murphy


Fruit size is a significant factor in the value of most citrus varieties grown for sale as fresh fruit. Production of fruit too small to market is most common in heavily over-cropped trees, a condition often observed in 'Murcott' (Citrus reticulata × C. sinensis) and other tangerine-types. Greatest improvements in fruit size result from cropload reduction relatively early in fruit development, but usually result in decreased yield, with increased fruit size not fully compensating for decreased numbers of fruit. In 2001, we conducted a trial on increasing fruit size of 'Murcott' with excessive fruit set. A randomized complete block factorial trial was established in which topping 0.5 m from a 4.6 m tall tree and application of 28 kg·ha[sup-] of KNO[sub3] were compared to non-treated controls. All fruit were harvested and sized from each of the treatment trees. KNO[sub3] treatments did not significantly affect any parameter measured. Topping decreased fruit per tree by 15% but increased mean fruit weight by 13%, resulting in no significant reduction in total yield. Cartons of fruit in the 80-120 count sizes were increased from 0.83 to 1.56 carton/tree but cartons 80-176 count sizes were not significantly increased. Peak production was at the 176 size class for all treatments. Since topping was conducted four months after bloom and yet virtually no yield reduction was apparent, reduced competition between fruit for photosynthates does not appear to fully explain the fruit size increase. It is proposed that reduced water stress, from reducing leaf area and associated transpiration, may be the principal mechanism for increasing fruit size in this experiment.


citrus reticulata; tangor; thinning; water relations

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283