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Predicting storage potential of apples using fruit mineral analysis

Make an assessment of the storage potential of Cox and Bramley apples from all orchards intended for storage by the use of mineral analysis.

 Sampling

Samples should be taken at random in the orchard from at least 20 trees usually by following a zig-zag path and taking one apple at random from alternate sides of successive trees.

  • Place the 20 apples in a clean polythene bag and label clearly to indicate cultivar, orchard, farm and sampling date.
  • If areas of the orchard have been managed differently, for example as regards soil or tree management or there are areas differing in terms of growth and cropping, then these should be sampled separately.
  • It may be necessary to segregate sections of the orchard at picking time and to allocate the fruit to different stores based on the indicated storage potential.

Early season analysis  

  • It is possible to make a preliminary prediction of storage disorders based on fruitlet analysis and on the fruit size that is predicted at harvest.
  • Advice is normally available from those providing the analytical service for fruitlets. It is not possible to draw up definitive analysis standards for fruitlets similar to those provided for fruit sampled at or just prior to harvest.
  • Samples of developing fruit should be taken early in the season e.g. early-mid July to predict the likely achievement of the desired mineral composition at harvest and the need for the application of nutrient sprays to increase the concentration of important elements such as phosphorus and calcium.
  • Data bases exist for Bramley and Cox which could be used to generate mineral standards for fruitlets in mid-July that relate to recommended standards for harvest fruit. These data relate to the same orchards sampled over a 7-year (Cox) or 9-year (Bramley) period that may provide more precise prediction than commercial data currently being used for this purpose.
  • Further statistical analysis of the survey data for Bramley and Cox is warranted in order to evaluate the predictive ability of models based on fruitlet (mid-July) or fruit (harvest) analysis.

 

Pre-harvest analysis

  • Further sampling for analysis is required at or just prior to harvest to check fruit size (mean fruit weight) and any categorisation of storage potential made earlier in the season. 
  • Sample fruit from Cox and Bramley orchards at harvest or up to 2 weeks prior to harvest.
  • Compare the analysis results with the recommended standards (see Tables 1 and 2).

 

Table 1.   Harvest mineral composition standards for Cox’s Orange Pippin apples grown in the UK

N

P

K

Ca

Mg

K/Ca

mg per 100 g fresh weight

 

50-70

 

11 min

 

130-160a

 

5c, 4.5b

 

5

 

30d, 35e max

 

 

a– maximum of 150 mg per 100 g for storage in 1.2% O2 (<1% CO2) later than    January

b – minimum for storage in 2% O2 (<1% CO2)

c – minimum for storage in air until the middle of October and 1.2% O2 (<1% CO2) later than January

d, e – maximum for storage in air and CA respectively. Commercially significant losses from bitter pit and late storage corking are likely at larger K/Ca ratios

 

Table 2. Harvest mineral composition standards for Bramley’s Seedling apples

grown in the UK

 

N

P

K

Ca

Mg

mg per 100 g fresh weight

 

60 max

 

9 min

 

105-115

 

5b, 4.5a

 

5

 

 

a –    minimum for storage in ventilated CA conditions of 8-10% CO2. Calcium requirement is likely to be lower for fruit stored in scrubbed low oxygen conditions of 6% CO2 + 2% O2, and particularly in 5% CO2 + 1% O2, although no definitive level has been set. In the interim a minimum level of 4 mg of calcium per 100 g is suggested.

b –    minimum for storage in air until November.

 

At harvest

  • Samples (20 fruit per orchard) at harvest can be taken directly from the bins prior to loading into store.
  • The sampling method should be similar to that described for taking samples for monitoring quality during the storage period.

 

Standards for Cox’s Orange Pippin and Bramley’s Seedling apples

Comprehensive survey experiments carried out over many years at East Malling resulted in the development of robust standards for Cox and Bramley (Tables 1 and 2).

  • Compliance with these standards is likely to minimise the occurrence of physiological disorders during storage. It is prudent to assign greater storage potential to consignments that exceed the minimum requirements for phosphorus and calcium.

Standards for cultivars other than Cox and Bramley

  • It may not be appropriate to apply the mineral composition standards for Cox and Bramley to other apple cultivars although the calcium threshold for bitter pit of 5 mg per 100 g fresh weight appears to be generally applicable. 
  • Concentrations of N, P, K and Mg are lower in Crispin, Golden Delicious, Spartan and Kent than in Cox and concentrations of P and K in Red Pippin, Gala and Jonagold are low compared with Cox.
  • Although lower concentrations of P and K can lead to breakdown in Cox and Bramley apples, they appear to have no adverse effects on the development of disorders in other cultivars.
  • The use of Cox standards for P and K for other dessert cultivars could exclude a large proportion of the crop from long-term storage and attempts to raise nutrient concentrations may result in no improvement in storage potential and in some cases storage quality may be compromised. For example, in Gala apples recent evidence suggests that any increase in K concentration may lower firmness and increase flesh breakdown.

 

Table 3. Average nutrient concentrations in Gala apples (sampled at harvest)

 

 

N

P

K

Mg

Ca

 

mg per 100g fresh weight

Gala

42

9.3

122

5

7.4

 

Notes:

·Gala is naturally low in P compared to Cox but this does not affect storage potential

·Gala is high in Ca and does not suffer from Ca-dependent storage disorders

·High K fruit may have an increased risk of breakdown

·Fruits higher in Ca and lower in K may be firmer ex-store

 

Table 4. Average nutrient concentrations in Gala and Braeburn apples (sampled two weeks prior to harvest)

 

 

N

P

K

Mg

Ca

 

mg per 100g fresh weight

Gala

45

10.2

106

5.3

9.6

Braeburn

52

11.9

102

5.1

6.3

 

Notes:

·Braeburn similar composition to Cox except that K concentrations appear lower

Suggest using Cox Ca threshold concentrations to judge storage potential of Braeburn apples