New chemical thinning strategies for stone fruit

Steenkamp, Human (2015-12)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Thinning of stone fruit, just as in any other deciduous fruit crop, plays an important role in producing fruit of the right size and quality. Hand thinning is highly labor intensive and time consuming, thus an alternative method of thinning is important to the industry. Chemical and mechanical thinning either alone or in combination could be the alternative. Two chemicals, 1-aminocyclopropane-1-carboxylic acid (ACC) and 6-benzyladenine (6-BA) were evaluated on Japanese plums, cling peaches and nectarines. In addition, the Darwin 300™, a mechanical string thinner, was also included in trials on early maturing ‘Alpine’ nectarine and ‘African Rose™’ plum. In all trials the objective was to reduce the required hand thinning during commercial hand thinning without compromising on yield and fruit quality. In Japanese plums we were able to reduce the hand thinning requirement significantly with both the ACC thinning and mechanical thinning strategies. Regarding ACC, cultivars differed in their sensitivity to the chemical and the recommended rate will differ for cultivars. ACC consistently reduced the required hand thinning linearly with increasing rate. The recommended rate of ACC for ‘African Rose™’ is 600 μl.L-1 and for ‘Laetitia’ 400 μl.L-1. For ‘Fortune’ a recommended rate could not be determined at this stage, thus further trials should be conducted. The Darwin 300™ reduced hand thinning significantly without reducing the yield significantly. Combining the Darwin 300™ with ACC 600 μl.L-1 in ‘African Rose™’ gave promising results with regard to hand thinning requirement and fruit size, without reducing yield efficiency significantly. No leaf drop was observed on Japanese plums, except in the pilot trial when applications were made at high temperatures, which should therefore be avoided. ACC was effective as thinning agent in cling peaches. In ‘Keisie’, the results were positive during both seasons, and ACC reduced the hand thinning requirement without reducing yield efficiency. The recommended rate of ACC for ‘Keisie’ is 600 μl.L-1. Slight leaf drop was observed. In ‘Sandvliet’, there was a significant reduction in fruit set, without reducing the required hand thinning. The reduction in fruit set led to a significant reduction in yield. Severe leaf drop was observed, indicating that cultivars differ in sensitivity to ACC. ACC would not currently be recommended for ‘Sandvliet’. In nectarines, ACC only thinned ‘Turquoise’ but not ‘Alpine’ or ‘August Red’ at the rates and phenological stage used, again indicating cultivar differences in sensitivity. In ‘Turquoise’, the highest ACC rate (500 μl.L-1) reduced fruit set per tagged shoot, as well as the hand thinning requirement, but this rate also reduced the total yield. The Darwin 300™ evaluated on ‘Alpine’ reduced fruit set significantly and the hand thinning requirement without reducing yield efficiency, indicating that mechanical thinning is a viable option in nectarines. Slight leaf drop was observed in all nectarine trials and ACC would not currently be recommended for nectarines. 6-BA was included to combat ACC-induced leaf drop and was partially successful. The reason for the differences observed in response to ACC between cling peaches and plums on the one hand, and nectarines on the other, cannot currently be explained.

AFRIKAANSE OPSOMMING: Uitdun van steenvrugte, net soos vir enige ander sagtevrugte soort, speel 'n belangrike rol in die produksie van vrugte met die regte grootte en gehalte. Uitdun van steenvrugte is hoogs arbeidsintensief en tydrowend, dus is dit belangrik om ʼn alternatief te vind vir die bedryf. Chemiese of meganiese uitdunning alleen of in kombinasie kan die alternatiewe wees. Twee middels, 1-aminosiklopropaan-1-karboksielsuur (ACC) en 6-bensieladenien (6-BA) is geëvalueer op Japanese pruime, taaipitperskes en nektariens. Daarby is die Darwin 300™, ʼn meganiese uitdunmasjien, ingesluit vir twee vroeë kultivars, nl. Alpine nektarien en African Rose™ pruim. Die doel van die proewe was om handuitdunning tydens kommersiële handuitdun te verminder, sonder om die opbrengs en vrugkwaliteit negatief te beïnvloed. Vir Japanese pruime kon ons die nodige handuitdunning beduidend verminder met beide die ACC en meganiese uitdun strategieë. Daar was wel ʼn verskil tussen die kultivars se sensitiwiteit teenoor ACC en die aanbevole konsentrasie sal verskil tussen kultivars. ACC het die benodigde handuitdunning vir al drie kultivars lineêr verminder met ʼn toename in konsentrasie. Die aanbevole konsentrasie van ACC vir ‘African Rose ™’ is 600 μl.L-1 en vir ‘Laetitia’ 400 μl.L-1. Vir ‘Fortune’ kan daar nog nie op hierdie stadium 'n konsentrasie aanbeveling gemaak word nie. Die Darwin 300™ behandeling het die benodigde handuitdunning beduidend verminder sonder om die opbrengs te beïnvloed. Die kombinasie van die Darwin 300 ™ met ACC 600 μl.L-1 het ook goeie resultate opgelewer wat handuitdunning en vruggrootte aanbetref sonder om die opbrengsdoeltreffendheid te verlaag. Geen blaarval was opgemerk by die pruime nie, behalwe in ʼn voorlopige proef toe die ACC toegedien is by hoë temperature, wat dus vermy moet word. Die effektiwiteit van ACC as uitdunmiddel van taaipitperskes was belowend. Vir ‘Keisie’ was die resultate positief vir beide seisoene, en ACC het handuitdunning verminder sonder om die opbrengs te beïnvloed. Die aanbevole ACC konsentrasie vir ‘Keisie’ is 600 μl.L-1. Effense blaarval is wel waargeneem. Vir ‘Sandvliet’ was daar 'n beduidende vermindering in vrugset, sonder dat handuitdunning verminder is. Daar was ook 'n beduidende afname in opbrengs en erge blaarval in die proef waargeneem. ACC sal tans nie aanbeveel word vir 'Sandvliet’ nie. Met nektariens het ACC net ‘n uitduneffek op ‘Turquoise’ getoon, maar nie teen die aangewende dosisse en ontwikkelingstadium op ‘Alpine’ of ‘Augustus Red’ nie. Dit dui daarop dat ACC kultivarspesifiek mag wees. In ‘Turquoise’ het die hoogste konsentrasie (500 μl.L-1) vrugset van gemerkte lote en die handuitdunning verminder, maar ook die totale opbrengs. Die Darwin 300 ™ het die vrugset van ‘Alpine’ asook die benodigde handuitdunning aansienlik verminder sonder om die opbrengs te verlaag. Effense blaarval was opgemerk in alle nektarien proewe. ACC sal nie aanbeveel word as uitdunmiddel vir nektariens nie. 6-BA was in die studie ingesluit om ACC-geïnduseerde blaarval teen te werk en was slegs gedeeltelik suksesvol. Die rede vir die verskille in respons tot ACC tussen pruime, perskes en nektariens kan nie tans verklaar word nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98026
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