Apple Maturity Assessments 2020: Week 4 Honeycrisp and Crimson Gala

Honeycrisp fruits are ready to start being harvested for long-term storage, showing increases in red skin color and starch index, and decreases in DA index values, firmness, and acidity, with respect to last week. On the other hand, Crimson Galas were already harvested at our sampling location, and displayed significant changes in most of the assayed maturity indices, as compared to last week, indicating that fruits at this stage should be harvested for shorter-term storage. All the information is summarized in Table 1.

Honeycrisp Results

This week we can observe differences in fruits grafted on M26 rootstock which received a ReTain application, as compared to last week, indicative of fruits that are ready to start being harvested for long-term storage. For more detailed results on specific quality parameters please read below:

Color

Surface color: Honeycrisp fruits presented an increase from 45% to 55% of red skin coloration, as compared to last week. These values are approaching what we observed last week on Honeycrisp fruits grafted on M9, without ReTain application.

Background color (DA index): DA index values decreased ~10% as compared to last week's assessments. Lower values are indicative of more advanced maturity.

Fruit firmness

As observed in the past weeks we have observed a decrease in ~1 lb/ week on the assayed Honeycrisp fruits; this week fruits are displaying average values around 14.5 lbs, indicative of fruits that are ready to be harvested for long-term storage.

Starch content

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 to evaluate the fruits. Fruits assayed this week presented an increase in their starch index values, with respect to last week's evaluation. Fruits with values ranging from 4-6 are recommended for harvesting for long-term storage.

Soluble solids contents (SSC)

SSC values are above 13% and have been maintained stable since last week's evaluation. In general, it is recommended to harvest fruits with readings around 12% to 14% SSC.

Acidity

Malic acid displayed a decrease from 0.5% to 0.4% when comparing last to this week's assessments, respectively.

Crimson Gala Results

In comparison to values obtained from last week's evaluation, Galas presented a significantly increased maturity, thus suggesting that this week fruit is ready to be harvested for shorter-term storage. We observed an increase in red skin coloration (87% vs 65%), significantly lower DA index values (readings of 0.2 vs 0.6), significantly higher starch index values (scale rating of 5.7 vs 3.3), almost ~2 lb decrease in terms of flesh firmness, and significantly increased soluble solids contents (13.7% vs. 12.2%), with no changes in acidity (0.4% malic acid).

Harvest in our sample location for Gala was completed last week for storage, and Honeycrisp fruit is starting to be harvested. We expect to continue evaluating both cultivars for one more week, as we are interested in studying changes occurring during fruit ripening on-the-tree as well as in evaluating the effects of different maturity stages at harvest on postharvest storage capacity. It is important to continue monitoring fruits by using different maturity indices and taking into consideration variations among locations, orchard blocks, plant growth regulator applications, and rootstock.

Table 1. Summary table of maturity assessments for Honeycrisp and Crimson Gala. Values in parentheses indicate the results from last week's monitoring. For fruit labeled with *, a ReTain application at ½ rate (½ pk/ac) was done on 8/27.

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