Apple Maturity Assessments 2021: Premiere Honeycrisp and Honeycrisp Week 3

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We continued assessing Premiere Honeycrisp on G11 and Firestorm Honeycrisp grafted on B9 (without any plant regulator application) located in the same farm in Smithsburg, MD. This week, Premiere Honeycrisp fruits are ready for harvesting for long-term storage, and is starting to display flesh firmness values targeted for harvesting fruit for short-term storage, while Firestorm Honeycrisp is still behind. As compared to last week, Premiere Honeycrisp significantly advanced its maturity with flesh starch disappearance values of 5.5, firmness values ~13.5lbs, DA index values of 0.6, skin red coloration ~50-60%, and soluble solids contents ~13%. The information is summarized in Table 1. It is important to note that we have been observing development of bitter pit in ~10% of the Premiere Honeycrisp fruits in our sample location already manifesting in the field.

Color

Surface color (eye-balling)

Premiere Honeycrisp fruits are showing an overall average 50 to 60% of red skin coloration, indicative of highly marketable fruit, while Honeycrisp fruits displayed values around 10%.

Background color (DA index)

Values are around 0.6 for Premiere Honeycrisp, while Firestorm Honeycrisp is >1 still. Readings of 0.6-0.7 are recommended for harvesting fruits for long-term storage, and we observed Premiere Honeycrisp fruit that already was in this range, thus ready for harvest for this purpose. An index of about 0.35 is targeted for harvesting fruit for short-term storage (which we have not observed yet). Fruits were measured with a DA meter, a device that measures the absorbance difference between 670 nm and 720 nm light. A higher DA index indicates a larger content of chlorophyll-a in the fruit skin.

Firmness

Fruit firmness

Premiere Honeycrisp fruit decreased their firmness values to around 13.5lbs, while Honeycrisp fruit are showing an average of 20lbs. In general, apples that are destined for long-term storage (>3 months) should be harvested with a firmness of at least 15lbs; while for fruit for shorter-term storage (1-2 months), a firmness of 13-15 lbs is appropriate. Premiere Honeycrisp fruit is already displaying harvest firmness for long-and short-term storage. Firmness was measured with a penetrometer with a 7/16-inch diameter plunger.

Starch

Starch content

Firestorm Honeycrisp fruit is at the lower end of the scale (1.5), while Premiere Honeycrisp fruits are showing a flesh starch disappearance value of 5.5. Premiere Honeycrisp fruit displayed an important increase in starch disappearance as compared with last week and is ready for harvesting for long-term storage. The common starch index rating system (Cornell chart) on a scale from 1 to 8, where 1 is full starch (all blue-black) and 8 is starch-free (no stain), was used. In general, on a 1 to 8 scale, values ranging from 4-6 are recommended for harvesting apples for long-term storage, while 6-7 for fresh market.

Sugars and Acids

Soluble solids contents (SSC)

SSC values, measured with a portable refractometer, are showing that Premiere Honeycrisp fruit are averaging 13%, while Honeycrisp is around 11.5%. In general, it is recommended to harvest fruits with readings around 12% to 14% SSC, a range already reached by Premiere Honeycrisp fruits.

Acidity

Our results show that Premiere Honeycrisp decreased its acidity values since last week to ~0.7%, while Firestorm Honeycrisp fruit was still constant at ~1%. A decrease in acidity content is an indicator of advancing maturity, the reason why this indicator is included in this report. Acidity was measured with an automatic titrator, quantifying malic acid (the major acid present in the juice of apples).

Table 1. Summary table of maturity assessments for Premiere Honeycrisp and Honeycrisp harvested from Smithsburg, Maryland. Values in parentheses indicate the results from last week's monitoring.