Apple Maturity Assessments 2020: Week 5 Honeycrisp and Crimson Gala
Honeycrisp fruits are being spot picked in our sampling location during this week, displaying accelerated ripening rates with important increases in red skin color (influenced by the low night temperatures that we have been experiencing), starch index, and soluble solids contents, while showing decreased DA index values and flesh firmness, as compared to last week assessments.
In the case of Crimson Galas, these fruits are tree-ripe, with significant increases in starch index values and soluble solids contents, and decreased firmness and DA index, with respect to last week. The increased ripening rates we observed this week can be associated with a decreased effect of ReTain, as we detected increased ethylene production in fruits from both cultivars as compared to previous weeks. Furthermore, a significant presence of cracks in fruits from both cultivars was noted. The information is summarized in Table 1.
Honeycrisp Results
Color
Surface color: Honeycrisp fruits presented an increase from 55% to 65% of red skin coloration, as compared to last week. These increases can be influenced by the cooler nights we have been experiencing during the past week.
Background color (DA index): DA index values decreased to 0.6 as compared to 0.8 from last week, indicative of more advanced maturity, due to more chlorophyll degradation.
Fruit firmness
Fruits have continued decreasing firmness values and this week they reached 12.9 lbs, displaying a higher decreased than the ~1 lb/ week that we have been reporting for the last weeks, indicative of fruits that are ripening at a faster rate, resulting from higher ethylene production.
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. Honeycrisp fruits this week displayed a starch index value of 5.3, another indicator of an accelerated ripening process as compared to the trends that we had observed the previous weeks.
Soluble solids contents (SSC)
SC values are around 14% and also increased since last week's evaluation. In general, it is recommended to harvest fruits with readings around 12% to 14% SSC.
Acidity
Malic acid has maintained stable at 0.4% with respect to last week's assessments.
Crimson Gala Results
Galas are presenting an advanced maturity and are ready for the fresh market. Fruits displayed significant increases in starch index values (Cornell scale rating of 7.2) and in soluble solids contents (reaching almost 15%), while decreasing their DA index values (indicative of almost complete chlorophyll degradation), and presenting ~3 lb decrease in flesh firmness with respect to last week. This accelerated ripening can also be due to the loss of the effect of ReTain, supported by significant increases in ethylene production in the fruits.
This will be the last evaluation we conduct for these two cultivars in our sampling location for this season. We expect to resume with maturity assessments for Fuji in the coming weeks. 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 rootstocks.
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.
