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Managing olive yield and fruit quality under South African conditions

Crous, Jacobus Johannes (2012-12)

Thesis (MScAgric)--Stellenbosch University, 2012.


ENGLISH ABSTRACT: Olives have been produced commercially in the Mediterranean-type climate of the Western Cape region of South Africa since the early 1900’s. As in the rest of the world, South African table olive producers struggle with alternate bearing. Naphthalene acetic acid (NAA) has been used since the 1950’s to thin table olives in California. To date, South African producers opted to tolerate rather than try to reduce the negative effects of alternate bearing. However, due to increased olive production, profit margins are decreasing and producers can no longer ignore the negative effects of alternate bearing. Since the efficacy of NAA as a thinning agent is modulated by environmental conditions and genotype, trials were conducted to evaluate the use of NAA on locally important cultivars under South African conditions. The main aim was to establish optimum application rates for ‘Barouni’, ‘Mission’ and ‘Manzanillo’. NAA decreased the fruit number per tree, thereby improving fruit quality (increased fruit size and a higher proportion black fruit in the case of ‘Mission’) in all three cultivars. Thinning did not affect the return bloom in any of the cultivars. In the case of ‘Barouni’, the lack of a return bloom response could be due to the low level of thinning achieved, while climatic conditions during flower development may be to blame for the lack of response in ‘Mission’ and ‘Manzanillo’. Although NAA application did not affect the income per hectare, profitability may increase as harvesting costs account for roughly 50% of the input costs. Based on our results, NAA at 200 mg L-1, applied 10 to 15 days after full bloom, is recommended for local conditions. This concentration is slightly higher than the application rates used in California. An even higher NAA concentration might be used when premium prices are paid for large fruit, as in the case of ‘Mission’ and ‘Manzanillo’. However, NAA at 400 mg L-1 seemed to decrease vegetative growth in ‘Mission’, which may decrease bearing positions for the next season. Earlier application should be considered for a heavy “on” crop while the concentration can be decreased or the spray time delayed to decrease thinning when an average crop is anticipated. Gibberellic acid (GA3) was applied during an “off” season to ‘Mission’ and ‘Manzanillo’ to determine when during the season floral induction is inhibited by the simulated seed produced hormone. GA3 had its greatest effect on the extent of flowering in ‘Manzanillo’ when applied at the time of endocarp sclerification in early December. It follows from this result that to prevent the negative effects of a crop load on flowering in the subsequent season, thinning has to occur before endocarp sclerification. Later application of GA3 in January and February also decreased flowering, but to a lesser extent than application in December. These later applications possibly decreased flower initiation in buds on shoots that continued growing for longer or they may also have interfered with flower differentiation. The effect of the reduced “on” crop in the 2010/2011 season in GA3-treated trees on yield in the 2011/2012 season still needs to be determined.

AFRIKAANSE OPSOMMING: Olywe word sedert die vroeë 1900’s kommersieel geproduseer in die Mediterreense tipe klimaat Wes-Kaap streek van Suid Afrika. Soos in die res van die wêreld, is alternerende drag ‘n reuse struikelblok vir Suid-Afrikaanse olyfprodusente. Anders as in California waar naftaleenasynsuur (NAA) reeds vanaf die 1950’s gebruik word om tafel olywe uit te dun, het Suid-Afrikaanse produsente tot op hede die gevolge van alternerende drag verduur eerder as om die negatiewe effekte daarvan te probeer verminder. Weens ‘n afname in winsgewendheid vanweë ‘n toename in olyfproduksie kan Suid-Afrikaanse olyfprodusente egter nie meer langer die negatiewe effekte van alternerende drag ignoreer nie. Die effektiwiteit van NAA as uitdunmiddel word beïnvloed deur omgewingstoestande asook deur die plant se genetika. Gevolglik is proewe onderneem om die gebruik van NAA te evalueer op plaaslik belangrike kultivars en onder Suid-Afrikaanse kondisies. Die hoofdoel van die proewe was om optimale toediening konsentrasies van NAA vir ‘Barouni’, ‘Mission’ en ‘Manzanillo’ te bepaal. NAA het die vruglading per boom verminder en daardeur vrugkwaliteit (vruggrootte asook ‘n groter proporsie swart vrugte in die geval van ‘Mission’) in al drie kultivars verbeter. In al drie kultivars het uitdunning egter geen effek op die volgende seisoen se blom gehad nie. In die geval van ‘Barouni’ kan die swak opvolgblom moontlik toegeskryf word aan die lae vlak van uitdun terwyl klimaatstoestande tydens blomontwikkeling moontlik die oorsaak was vir die swak reaksie van ‘Mission’ en ‘Manzanillo’. Alhoewel toediening van NAA nie die bruto inkomste per hektaar verhoog het nie, kan winsgewendheid moontlik toeneem aangesien oeskoste ongeveer 50% van insetkostes uitmaak. Gebaseer op die resultate van die studie, word NAA toediening teen 200 mg L-1, 10 tot 15 dae na volblom, aanbeveel vir plaaslike toestande. Hierdie konsentrasie is effens hoër as konsentrasies wat in Kalifornië gebruik word. Selfs hoër NAA konsentrasies kan toegedien word wanneer ’n premium betaal word vir groter vrugte, soos in die geval van ‘Manzanillo’ en ‘Mission’. NAA teen 400 mg L-1 het egter vegetatiewe groei in ‘Mission’ verlaag en dit kan moontlik lei tot ‘n vermindering in draposisies in die volgende seisoen. Vroeër toediening moet oorweeg word wanneer ‘n groot “aan” oes verwag word, terwyl die NAA konsentrasie verminder of toediening uitgestel kan word ten einde uitdunning te verminder indien ‘n gemiddeld oes verwag word . Gibberelliensuur (GA3) is in die “af” seisoen toegedien op ‘Mission’ en ‘Manzanillo’ om vas te stel wanneer gedurende die seisoen saad-geproduseerde hormone blominduksie inhibeer. Die grootste effek op blominduksie van ‘Manzanillo’ is verkry met toediening tydens pitverharding gedurende vroeë Desember. Om die negatiewe effek van ‘n hoë vruglading op die volgende seisoen se blom te voorkom, moet vruguitdunning dus voor pitverharding geskied. Later toediening van GA3 in Januarie en Februarie het ook blom verminder, maar tot ‘n mindere mate as toediening in Desember. Hierdie later toedienings het moontlik blominisiasie van knoppe wat later gevorm het geïnhibeer of kon moontlik blomdifferensiasie negatief beïnvloed het. Die effek van die verlaagde “aan” jaar in die 2010/2011 seisoen in reaksie op GA3 toediening op opbrengs in die 2011/2012 seisoen moet nog bepaal word.

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