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Effect of pre harvest Foliar sprays of Boron and Retain® for improvement of quality parameters of apricots (Prunus armeniaca L.) in Tasmania

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Mehta, B (2013) Effect of pre harvest Foliar sprays of Boron and Retain® for improvement of quality parameters of apricots (Prunus armeniaca L.) in Tasmania. PhD thesis, University of Tasmania.

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Abstract

Techniques to improve fruit firmness and quality in apricot would enhance marketability. Apricot is considered as one of the most delicious temperate fruits, and good balance of sugars and acids and a strong apricot aroma are the major determinants of exceptional fruit quality. Studies were conducted in three different varieties of apricot (Prunus armeniaca L.) namely ‘Rival’, ‘Goldrich’ and ‘Orangered® Bhart’ to determine if pre-harvest foliar applications of different concentrations of boron and ReTain® influences fruit quality and fruit yield. Firmness and sugars were of specific concern as fresh apricot has a very short shelf life of five to six days and transfer of fruit from farm to market within limited time span is a major concern. Firm fruit with adequate sweetness will allow Tasmanian orchardist to export more fruit.
The selection of the varieties for the main study was done by screening nine different varieties based on their maturity periods and availability of maximum samples. ‘Orangered® Bhart’ is an early harvested variety and ‘Rival’ and ‘Goldrich’ are middle harvested varieties. For this experiment, treatments consisted of four sprays of different concentration of boron in the form of Solubor (20% boron) followed by two sprays of Retain®. The pre-harvest foliar sprays were applied to trees exhibiting B deficiency as follows: (i) applied before full bloom (at green and white bud stage, and when 1-5% of flowers was at full bloom), (ii) at petal fall stage after flowering (iii) 7 days after petal fall and (iv) 14 days after petal fall. Trees sprayed with water served as controls. Boron was applied at 1.2 Kg ha-1, 1.8 kg ha-1, 2.4 kg ha-1 and 3.0 kg ha-1 for all varieties of apricots. ReTain® application rates were 0.40 kg ha-1, 0.65 kg ha-1 and 1.0 kg ha-1 and was sprayed twice (v) 7 days before harvest (BCCH scale 87) and (vi) 14 days before harvest (BCCH scale 88).
Foliar boron application improved the number of flower clusters by 12-15% in Rival, 2-12% in Goldrich and 4-12% in Orangered® Bhart varieties and the fruit set from 2 - 5% in Rival, 2- 8% in Goldrich and 2-8% in Orangered® Bhart variety. Thus, the sprayed trees had a greater potential to be healthy and productive with decrease in fruit drop.
All three varieties are significantly different from each other in terms of quality parameters. ReTain® eliminated the effects of Boron. ReTain® improved the firmness of ‘Rival’ and ‘Goldrich’ varieties from 10-20% and 6 – 29% respectively with decreases in sugars from 7 - 20% and 4-12%. The titrable acidity increased with the combined effect of boron and ReTain ® treatments. Boron levels at four different stages of spraying were measured with Induced Couple Plasma-Optical Emission Spectroscopy (ICP-OES). This was done in order to examine the absorption of boron in response to the foliar application. The results show increase in boron absorption of 13-48% in fruits of Goldrich followed by 13-23% in fruits of Orangered® Bhart. Boron sprays did not affect the Nitrogen (N) and magnesium (Mg) in plant tissues.
Aroma compounds are present in raw foods either as free compounds or glycosidically bound (aroma precursors).To investigate the difference in volatile constituents due to the treatment effects, the volatile compounds were investigated by means of SPME (Solid Phase Micro Extraction) using Carboxen-Polydimethylsiloxane fibers. The free aroma compounds were identified by Gas Chromatography and Mass Spectroscopy (GC-MS), finding common compounds such linalool, α-terpineol, β-ionine, γ-decalactone and 26 other compounds. Fenchone was used as internal standard. The Multivariate analysis showed a significant effect on the volatiles released from different cultivars. The amount of esters, lactones and terpenic acids released were more than carbonyl compounds. Though more than 60 compounds were eluted with SPME, 30 identified volatiles were measured in the process.
Successful development of new rural industries depends on understanding and meeting consumer needs. A study was carried out to probe consumer understanding of apricot fruit quality and their perceptions to sensory attributes. The results were correlated to instrumental measurements. Three different varieties of apricot with two different treatments of Boron and Boron + ReTain® making a total set of nine samples were used as tastings for the consumers. Apricots were harvested at a similar maturity stage according to commercial practices. Analysis and sensory assessments were carried out on equivalent fruits from uniform samples.
Despite the variability of response of assessors, significant differences were found between attributes of different treatments. Consumer preferences for some quality attributes of flavor, firmness and sugar correlated with instrumental analysis. Even though Rival is the firmest variety according to instrumental analysis, Orange red sprayed with ReTain® scored highest for overall satisfaction according to consumer preferences. These findings indicate that preharvest boron and ReTain® sprays can successfully increase apricot fruit numbers, flower clusters and fruit quality respectively.

Item Type: Thesis (PhD)
Keywords: Prunus armeniaca, Boron, ReTain, volatiles, SPME, consumer perceptions, fruit quality measurements
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Date Deposited: 02 Oct 2013 02:03
Last Modified: 15 Sep 2017 01:06
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