Honeycrisp Fruit Maturity - Brief Report - Sept 27

Tuesday, September 27, 2022

This update includes a brief update on Honeycrisp maturity at the two sites being monitored in North Medford.

Important Note - The following information is for general industry purposes only. Growers are encouraged to use their own discretion to harvest trees that are exhibiting delayed colour development or exhibiting maturity indices that disagree with what is being reported here. Values were measured on an average of fruit that were representative of the block's crop load and tree vigour. Fruit representative of size and colour were taken from all sides but not from the interior where maturity is expected to be delayed.

Table 1: Maturity indices for Honeycrisp fruit sampled in North Medford on Sept 27.

The average DA value for measured fruit in the regions is within the target of 0.60 to 0.35. DA values will be noticeably different between the most mature and least mature fruit on a tree and these ratings represent the overall average. ReTain-treated fruit may not provide results with the DA meter that match other maturity indices like starch. 

Over the last week, starch conversion to sugars has progressed by about 1 index point (Figure 2). Soluble solids increased by 0.5%. Firmness has decreased by about 1 lb of pressure in non-ReTain treated fruit and was unchanged in ReTain treated fruit being measured. Colour has increased by about 5-15%.

Figure 2: The visual results of starch-iodine tests on a ten-fruit sample. Average ratings are reported in Table 1. Sampled in North Medford on Sept 27.

About each measurement:

Starch Index - Starch is converted to sugars as ripening progresses. The starch-iodine test is used because iodine binds to starch molecules turning them blue/black, whereas sugars are not stained and remain clear. The Cornell chart on a scale of 1 to 8 was used above and values are an average of ten representative samples from each block.

Soluble Solids - Approximates the percentage of sugar content of the fruit. Measured using a digital refractometer. Values are an average of ten representative samples from each block.

DA Meter - The delta absorbance (DA) value is related to the chlorophyll content of the peel. AAFC researchers in Kentville developed a protocol for Honeycrisp. Values above 0.60 are immature, values 0.6 to 0.36 are ideal for long term storage, and values below 0.35 are best for short term storage because they are more prone to storage disorders. Values shown above are the average of twenty fruit taken throughout a block, with readings taken on both the red and green sides.

Firmness - Measured using a handheld penetrometer with a 7/16 inch diameter plunger on ten representative fruit.

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