Aspects of fruit size and quality in citrus

Mzini, Loyiso L. (2002-12)

Thesis (MScAgric)--Stellenbosch University, 2002.

Thesis

ENGLISH ABSTRACT: Fruit size can be a problem in 'Clementine' mandarin and 'Valencia' orange in the Western Cape region of South Africa. Small fruit is not only unacceptable to the consumer but is also more difficult and expensive to harvest. Means of alleviating this problem is to manage the crop load. Hand thinning trials were conducted to evaluate the effect of timing and severity thereof in enhancing fruit size. The benefits of enhancing large fruit size was obtained by a heavy-thinning (60% fruitlet removed) treatment, but the actual benefits were offset by a reduction of total yield. Yield was reduced up to 30% when heavy thinning treatments were applied. No effect on early or late treatments were obtained since the trial was conducted rather late (4 to 6 weeks after the physiological fruit drop period) to obtain the desirable results. However, better packouts are expected with thinning treatments since blemished fruit are also removed. The effect of multiple 2,4-dichlorophenoxy propionic acid (dichlorprop) sprays were also evaluated on 'Nules Clemetine' mandarin. Comparing multiple sprays with a single spray, it was observed that more than one spray was no better in improving fruit size. The use of multiple dichlorprop sprays resulted in no additional yield reduction, while internal fruit quality 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 large fruit (>55 mm) was not significantly affected. In the 'Valencia' orange trials, during the first year, dichlorprop was sprayed relatively late (fruit diameter: 19 mm). No fruit size, yield and internal 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 observed that late sprays had no effect on fruit size, whereas fruit size (48 fruit per carton) was significantly increased by early sprays. This implies that the dichlorprop effect on fruit size is during the early stages of fruit development, just after or during the late stage of the physiological fruit drop period. Yield was drastically reduced by up to 35%, which affected the actual kilograms of large fruit adversely in some treatments. Juice percentage was inconsistent and tended to be reduced by dichlorprop application. Dichlorprop tended to increase TSS slightly in year one and significantly so in year two, but did not affect the TSS:TA ratio. The use of Orchex mineral oils as surfactant at 150 mL. 100 L-1 was effective and seemingly allowed lower rates of dichlorprop to be used. Therefore, surfactants seemed to 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 the later stage of fruit development. Observations indicate that dichlorprop-sprayed fruit at 50 mg. 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 shaded with brown paper bags. However, dichlorprop-sprayed fruit at 100 mg. L-1 , even though exposed to light did not show significant differences with unsprayed in both shaded and exposed conditions. Therefore, no consistent effect of dichlorprop was established on total carotenoid content of the rind.

AFRIKAANSE OPSOMMING: Vruggrootte van 'Clementine' mandaryn en 'Valencia' lemoene kan 'n probleem wees in die Wes Kaap area van Suid Afrika. Klein vrugte is nie net onaanvaarbaar vir die verbruiker nie, maar is ook moeilik om te oes. Vrugdrag manipulasie is een manier om hierdie probleem te beheer. Hand uitdunningsproewe is uitgevoer om die effek van tyd en graad van uitdunning op vruggrootte te bepaal. Strawwe vruguitdunning (60% van vruggies verwyder) het groter vrugte tot gevolg gehad maar het gelei tot 'n verlaagde opbrengs. Opbrengs is tot soveel as 30% verlaag met die strawwe vruguitdunning. Vroeë en laat behandelings het egter geen effek gehad nie, aangesien die proewe te laat uitgevoer is (4 tot 6 weke na die fisiologiese vrugvalperiode) om die gewenste effek te verkry. Beter uitpak word verwag na uitdunning, aangesien vrugte met letsels ook verwyder word. Die effek van veelvuldige 2,4-dichlorofenoksie-propioonsuur (dichlorprop) spuite IS ook geëvalueer op 'Nules Clementine' mandaryn. Daar is geen verskil gevind tussen enkel en veelvuldige spuite in terme van vruggrootteverbetering nie. Die gebruik van veelvuldige dichlorprop spuite het nie tot 'n verlaging in opbrengs gelei nie, en interne vrugkwaliteit is ook nie beïnvloed me. Die beste resultate is verkry met die 50 mg. L-1 dichlorprop behandeling. Die gebruik van dichlorprop saam met verskillende benatters is op beide 'Clementine' mandaryn en 'Valencia' lemoene geëvalueer. Vruggrootte het toegeneem vanaf 50 mg. L-1 tot 100 mg. L-1 • Opbrengs was net in sekere gevalle verlaag en dan sonder 'n betekenisvolle verskil in groot-vrug produksie (>55 mm: Clementines). Tydens die eerste jaar van die 'Valencia' lemoen proef is die dichlorprop relatief laat gespuit (vrug deursneë: 19 mm). Daar was geen effek op vruggrootte, opbrengs en interne vrugkwaliteit nie. Tydens evaluasie van vroeë en laat bespuitings die volgende jaar is waargeneem dat laat bespuitings geen effek op vruggrootte gehad het nie, terwyl vruggrootte (48 vrugte per karton) betekenisvol verhoog is deur die vroeë bespuitings (Vruggrootte voor bespuiting = 8 en 12 mm, onderskeidelik). Dit impliseer dat dichlorprop se effek op vruggrootte gedurende die vroeë stadiums van vrugontwikkeling is, net na of gedurende die laat stadiums van die fisiologiese vrugvalperiode. Opbrengs is drasties verlaag deur dichlorprop, tot soveel as 35% wat die kilogram groot vrugte negatief beïnvloed het in sommige behandelings. Sappersentasie was nie konsekwent affekteer nie, maar is verlaag deur die dichlorprop bespuitings. Dichlorprop het die TSS effens verhoog in beide jare, maar het geen effek gehad op die TSS:TA verhouding nie. Die gebruik van Orchex minerale olie as benatter was effektief by 150 mL. 100 L-1 , en laat klaarblyklik die gebruik van dichlorprop by laer konsentrasies toe. Dus, kom dit voor dat benatters die potensiaal het om die effektiwiteit van dichlorprop te verbeter wat lei tot 'n verlaging in toedieningskoste. Die dichlorprop gespuite vrugte is gebruik om karotenoïed-inhoud van die skil te meet tydens die laat stadiums van vrugontwikkeling. Vrugte gespuit met dichlorprop teen 'n konsentrasie van 50 mg. L-1 het 'n beter karotenoïed-inhoud in beide 'Clementine' mandaryn en 'Valencia' lemoene tot gevolg gehad. Vrugte blootgestel aan lig het ook 'n hoër karatenoïedkonsentrasie gehad as vrugte wat met bruin papiersakke bedek was. Dichlorprop bespuite vrugte teen 100 mg. L-I, alhoewel blootgestel aan lig, het geen betekenisvolle verskil gehad in vergelyking met onbespuite vrugte nie. Dus is daar geen konsekwente effek van dichlorprop op karotenoïde inhoud van die skiI waargeneem nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/52699
This item appears in the following collections: