Effects of fruit position within a tree and orchard location on fruit quality & storage disorders

Does growing region, fruit position and sun exposure influence the susceptibility of nectarines to storage disorders during sea freight export?

Objective:

Determine whether climatic and tree factors due to growing region, fruit position within trees, and fruit exposure to solar radiation, as indicated by fruit skin colour, effect the susceptibility of nectarines to storage disorders during simulated sea freight export.

On this page:

Commercial implications of findings

Key research findings

Summary of experimental findings

Experimental methods

Key results

Commercial implications of findings:

Fruit growing conditions such as shading and position within trees are potential pre-harvest factors that can influence fruit quality and storage potential (Crisosto et al., 1997; Lopresti et al., 2014) but little information is available on the impacts of orchard and tree factors on stone fruit quality, and particularly fruit susceptibility to storage disorders after cool storage. Utilising ‘Majestic Pearl’ and ‘September Bright’ nectarines grown in Swan Hill and Tatura, Victoria, the effects of growing region, tree position (i.e., top versus bottom) and fruit colour (i.e., low versus high blush) on incidence of severe flesh browning (FB) were determined during sea freight simulations. Among both cultivars fruit grown in Swan Hill had higher susceptibility to storage disorders than those grown in Tatura, with the effect of growing region greatest among ‘Majestic Pearl’ nectarine. Highly blushed fruit were generally more susceptible to storage disorders but more so among fruit grown in Swan Hill whereas fruit position in trees was of less importance in influencing fruit susceptibility to severe flesh browning. Based on these preliminary findings, growers need to consider and understand the influence of growing region, and fruit exposure (and canopy/training systems) on storage potential during sea freight export, and the potential increase in fruit susceptibility to storage disorders due to warmer growing conditions and greater exposure to solar radiation during fruit growth.

Key research findings:

• ‘Majestic Pearl’ and ‘September Bright’ nectarines grown in Swan Hill were highly susceptible to storage disorders as measured by incidence of severe FB compared to fruit grown in Tatura, among fruit of similar harvest maturity and skin colour.
• Highly blushed ‘Majestic Pearl’ from both the top and bottom of trees were more susceptible to severe FB than low blush fruit, as were ‘September Bright’ nectarine harvested from Swan Hill, but little effect of fruit blush was observed among fruit of either cultivar grown in Tatura.
• Among ‘Majestic Pearl’ nectarine grown in Swan Hill, fruit from the top of trees were marginally more susceptible to severe FB than fruit from the bottom half of trees but among both cultivars grown in Tatura the impact of fruit position within trees on susceptibility to storage disorders was minimal.

Summary of experimental findings:

The effect of growing region, fruit position within trees and fruit skin colour (i.e., skin blush), as an indirect indicator of fruit exposure to solar radiation, on fruit storage potential and quality was explored utilising ‘Majestic Pearl and ‘September Bright’ nectarines grown commercially in Swan Hill, and within the AVR stone fruit research orchards in Tatura, Victoria.

For each cultivar and growing region, fruit were picked during commercial harvest from the top and bottom of five adjacent trees, and within each tree position, classified as high or low blush based on visual skin colour assessment (Fig.1). A weighted fruit colour score between 1 and 10 was calculated for each fruit based on skin area that was fully blushed (i.e., score of 10), and the blush intensity of the background colour, with a higher colour score indicating fruit with both greater full blush and higher background colour intensity moving away from green to yellow/red.

‘September Bright’ nectarine from Swan Hill were purchased from a grower after grading and so no classification by tree position was possible in this case. After colour classification, all fruit were cool-stored in perforated high humidity liners for either 35 or 42 days at 2 °C to simulate sea freight export durations  and held at 18 °C for 4 days to simulate a short marketing period. FB severity score was determined as a measure of the degree of chilling injury among fruit that has been associated with incomplete fruit ripening and poor eating quality due to flesh mealiness and negative changes in texture. FB severity after the marketing period was scored by assigning a severity rating to each fruit where 0 = none, 1 or 2 = moderate, and 3 or 4 = severe, with the incidence of any, moderate and severe FB calculated for each storage replicate of 20 fruits. Fruit with severe FB symptoms would be commercially unmarketable and not suitable for eating by consumers. Prior to cool storage mean fruit maturity as measured via Index of Absorbance Difference (I_AD) and skin colour (i.e., blush area and intensity) within a cultivar were comparable between growing regions although fruit harvested from Tatura were significantly smaller than fruit grown commercially from Swan Hill (Table 1).

Among ‘Majestic Pearl’ nectarines stored for 35 or 42 days at 2 °C to simulate sea freight export and ripened at 18 °C for 4 days, growing region had the greatest effect on susceptibility to chilling injury as measured via FB, with relatively high incidence of severe FB in fruit grown in Swan Hill when averaged across two storage durations, compared to fruit of similar harvest maturity and skin colour grown in Tatura (Fig. 2). Fruit grown in Tatura were consistently less susceptible to severe FB when compared to Swan Hill fruit with similar weighted colour score, and from the same position within trees, suggesting that growing region was the main factor impacting on fruit susceptibility to storage disorders.

Among Majestic Pearl grown in Swan Hill highly blushed fruit from both the top and bottom of trees had significantly higher incidence of severe FB, whilst both highly blushed and low blush fruit from the bottom of trees were less susceptible to severe FB during storage compared to fruit from the tops of trees. Among less susceptible fruit grown in Tatura, and unlike fruit grown in Swan Hill, little difference in severe FB incidence was observed between highly blushed and low blush fruit within each tree position.

Among graded ‘September Bright’ nectarine grown in Swan Hill highly blushed fruit were more susceptible to severe FB than low blush fruit with high incidence of severe FB observed in highly coloured fruit after cool storage for 35 or 42 days, and a marketing period (Fig. 3). After both cool storage durations severe FB incidence was over 50 % higher in relative terms compared to low blush fruit, with only slight increases in severe FB with increasing storage duration, and little difference in fruit maturity between high and low blush fruit after ripening. ‘September Bright’ nectarines grown in Tatura were less susceptible to severe FB compared to those grown in Swan Hill with incidence of severe FB increasing with storage duration in both high and low blush fruit, and in fruit from both the top and bottom of trees (Fig. 4).  After cool storage for 35 days fruit from the top of trees appeared to be more susceptible to severe FB compared to fruit from the bottom of trees regardless of skin colour, but this difference was not observed after 42 days of cool storage in highly susceptible fruit, whilst little difference in flesh browning incidence was observed between high and low blush fruit within each tree position.

Interestingly both high and low blush ‘September Bright’ nectarines harvested from Tatura had higher weighted colour scores than equivalent fruit in Swan Hill but less overall severe FB suggesting that in these trials growing region was the main factor influencing fruit susceptibility to storage disorders.

References

Crisosto C., R. Johnson, T. DeJong and K. Day (1997). Orchard factors affecting postharvest stone fruit quality. HortScience, 32(5):820-823.

Lopresti J., I. Goodwin, B. McGlasson, P. Holford and J. Golding (2014). Variability in size and soluble solids concentration in peaches and nectarines. Horticultural reviews, 42:253-312.

Experimental methods:

Key results:

Figure 1. ‘September Bright’ nectarines  at harvest that were classified into high and low blush groups (top and bottom, and middle two rows, respectively) prior to cool storage.

Table 1. Mean harvest quality parameters among high and low blush fruit calculated from measurements on 80 fruit per cultivar and growing region.

*September Bright fruit from Swan Hill were purchased from the grower after grading

Figure 2. Effect of growing region, tree position and fruit colour category on incidence of severe flesh browning among ‘Majestic Pearl’ nectarines with mean colour scores provided for comparison among treatments; error bars show ± 95% confidence interval of each mean.

Figure 3. Effect of storage duration and fruit colour category on incidence of severe flesh browning, and mean colour scores for each blush category and storage duration, among commercially harvested and graded ‘September Bright’ nectarines grown in Swan Hill; error bars show ± 95% confidence interval of each mean.

Figure 4. Effect of storage duration, tree position and fruit colour category on incidence of severe flesh browning among ‘September Bright’ nectarines harvested from Tatura with mean colour scores provided for comparison among treatments; error bars show ± 95% confidence interval of each mean.

Acknowledgement

The Serviced Supply Chains II project (AM21000) is funded by the Hort Frontiers International Markets Fund, Avocado and Strawberry research and development levy, and contributions from the Australian Government, with co-investment from the Department of Agriculture and Fisheries, Queensland (DAF), the Department of Energy, Environment and Climate Action, Victoria (DEECA), the Department of Industry, Tourism and Trade, Northern Territory (DITT), the Department of Primary Industries and Regional Development, Western Australia (DPIRD), Pinata Farms Pty Ltd and Summerfruit Australia Ltd. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.

For more information, contact John Lopresti on john.lopresti@agriculture.vic.gov.au

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