Apple Maturity Assessments 2020: Week 3 Honeycrisp and Crimson Gala

All of the fruits were harvested from Aspers, PA. Honeycrisp fruits grafted on M9 and not treated with ReTain are ready to be harvested for storage, while fruits treated with the plant growth regulator and grafted on M26 are presenting a delayed maturity, with main differences on red coloration, DA, and starch index values. Most of the maturity indices assessed for Crimson Gala treated with ReTain are indicative of fruit ready for harvesting for storage. It is worth mentioning we did observe some fruit cracking in Galas as a result of fruit expansion due to excessive rainfall.

All the information is summarized in Table 1 below.

Honeycrisp Results

This week we can observe differences among fruits grafted on M9 and M26 rootstocks at Aspers, PA in combination with fruits that received and did not receive a ReTain application. Fruits grafted on M9 without the plant growth regulator application are ready to be harvested for storage, whereas fruits grafted on M26 and with ReTain application show a delayed maturity trend for harvest. For more detailed results on specific quality parameters please read below:

Color

Surface color: Honeycrisp fruits with and without ReTain application in both rootstocks presented a 45% and 55% of red skin coloration, respectively. Yet, in fruits with ReTain application, we observed an important increase since last week (30% to 45%).

Background color (DA index): There are significant differences between fruits without and with ReTain as values ranged between 0.6 and 0.9, respectively. Lower values are indicative of more advanced maturity, as was the case for fruits grafted on M9 without ReTain application, which are ready to be harvested for storage. Nevertheless, we see an important decrease in values in fruit treated with ReTain since our last evaluation (from 1.2 to 0.9). DA index readings of 0.60-0.70 are recommended for long-term storage apples.

Fruit firmness

All evaluated fruits, irrespective of ReTain application, and rootstocks are displaying firmness values around 15-15.5lbs, indicative of fruits that are ready to be harvested for long-term storage. A significant decrease in firmness was observed for fruit that received the ReTain application (16.4 to 15.5lbs) since last week's evaluation.

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. Important differences were observed between Honeycrisp fruit with (index=6.6) and without (index=2.9) ReTain application. Fruits with values ranging from 4-6 are recommended for harvesting for long-term storage.

Soluble solids contents (SSC)

SSC values are above 13% in all cases. In general, it is recommended to harvest fruits with readings around 12% to 14% SSC.

Acidity

Malic acid presented were the same irrespective of rootstock and ReTain application. Although we can see a decrease in acidity in fruit treated with ReTain from our values from last week, as expected.

Crimson Gala Results

In general, in comparison to values obtained from last week's evaluation, Galas presented increased red skin coloration (65% vs 60%), lower DA index values (readings of 0.6 vs 0.9), higher starch index (scale rating of 3.3 vs 2.7), increased soluble solids contents (12.2% vs. 11.9%), maintained their acidity (0.4% malic acid), and decreased their flesh firmness values (20lbs vs. 21lbs). Most of the maturity indicators for Gala are suggesting that the fruit is ready to harvest for long-term storage.

We will continue evaluating Honeycrisp and Crimson Gala from PA treated with ReTain, whose harvest at our sample location is anticipated to happen close to each other. It is important to continue monitoring fruits by using different maturity indices and taking into consideration variations among locations, orchard blocks, plant growth regulator application, 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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