Managing olive yield and fruit quality under South African conditions

[摘要] ENGLISH ABSTRACT: Olives have been produced commercially in the Mediterranean-type climate of theWestern 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, SouthAfrican producers opted to tolerate rather than try to reduce the negative effects of alternatebearing. However, due to increased olive production, profit margins are decreasing andproducers can no longer ignore the negative effects of alternate bearing.Since the efficacy of NAA as a thinning agent is modulated by environmental conditionsand genotype, trials were conducted to evaluate the use of NAA on locally importantcultivars under South African conditions. The main aim was to establish optimum applicationrates 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 thecase of 'Mission') in all three cultivars. Thinning did not affect the return bloom in any of thecultivars. In the case of 'Barouni', the lack of a return bloom response could be due to thelow level of thinning achieved, while climatic conditions during flower development may beto blame for the lack of response in 'Mission' and 'Manzanillo'. Although NAA applicationdid not affect the income per hectare, profitability may increase as harvesting costs accountfor 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 slightlyhigher than the application rates used in California. An even higher NAA concentrationmight 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 applicationshould be considered for a heavy 'on crop while the concentration can be decreased or thespray 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 seedproduced 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 thisresult that to prevent the negative effects of a crop load on flowering in the subsequentseason, thinning has to occur before endocarp sclerification. Later application of GA3 inJanuary and February also decreased flowering, but to a lesser extent than application inDecember. These later applications possibly decreased flower initiation in buds on shootsthat continued growing for longer or they may also have interfered with flowerdifferentiation. The effect of the reduced 'on crop in the 2010/2011 season in GA3-treatedtrees on yield in the 2011/2012 season still needs to be determined.

[发布机构] Stellenbosch University