**3. Results**

#### *3.1. Effect of PGR Application on Fruit Ripening*

In both cultivars, the proportion of green fruit decreased while that of ripe fruit increased over the duration of the experiment (Figure 1). In Premier, ethephon-treated fruit had a lower proportion of green fruit than that in the control from 4 days after treatment (Figure 1A). At this stage, the proportion of pink fruit was higher in ethephon-treated fruit (Figure 1B). The proportion of ripe fruit was significantly higher in the ethephon treatment from 7 days after treatment compared with the control (Figure 1C). At 7 days after treatment, 42% of the fruit were ripe in the control compared with 61% in the ethephon treatment. In contrast, treatment with ABA did not affect the proportion of green or ripe fruit but transiently increased the proportion of pink fruit at 7 days after treatment, compared with the control (Figure 1B). Similarly, treatment with MeJA did not alter the proportion of green and ripe fruit compared with the control, but increased the proportion of pink fruit at 2 days and 7 days after treatment (Figure 1B).

**Figure 1.** Effect of preharvest treatments with water (contol), ethephon, abscisic acid (ABA), and methyl jasmonate (MeJA) on ripening of rabbiteye blueberry, Premier (**A**–**C**) and Powderblue (**D**–**F**). Values are means and standard errors of four replicates. Within each assessment period, means with the same letter are not significantly different according to ANOVA and Tukey's HSD (α = 0.05).

In Powderblue, the doses of application of ABA and MeJA were higher (see Section 2) as these PGRs did not appear to affect ripening in Premier at lower doses of application. The PGR applications generally resulted in similar effects on Powderblue fruit ripening as in Premier, with a few exceptions (Figure 1D–F). The proportion of green fruit was lower (Figure 1D), and ripe fruit was higher (Figure 1F) than in the control in ethephon-treated fruit starting from 4 days after treatment until the end of evaluation; and, the proportion of pink fruit was higher at 4 days after treatment (Figure 1E). At 4 days after treatment, while only 33% of the fruit were ripe on the control plants, around 58% were ripe in response to the ethephon treatment (Figure 1F). Application of ABA did not affect the proportion of green or ripe fruit compared with the control but increased the proportion of pink fruit from 4

days after application (Figure 1E). At the rate of ABA used in this study (1000 mg <sup>L</sup>−1), phytotoxicity symptoms were observed in leaves (data not shown). Application of MeJA did not alter the proportion of green, pink, or ripe fruit at any stage after treatment in comparison with the control (Figure 1D–F).

#### *3.2. Effect of PGR Application on Fruit Color*

None of the fruit color-related parameters were significantly different among the PGR treatments in Premier at 1 day after harvest (Table 1). In Powderblue, treatment with ethephon and ABA also did not alter any of the fruit color-related parameters with respect to the control treatment at 1 day after harvest. In response to MeJA treatment, however, the parameters L\*, which measures the lightness, and b\*, which measures yellow/blue color, were higher and lower respectively, indicating lighter and greater blue fruit color than in the control (Table 1).

**Table 1.** Effect of preharvest treatment with water (control), ethephon, abscisic acid (ABA), and methyl jasmonate (MeJA) on fruit color after 1 day of cold storage at 4 ◦C in Premier and Powderblue blueberry.


z Means followed by the same letter within a column are not significantly different, according to Tukey's HSD (α = 0.05).

#### *3.3. Effect of PGR Application on Fruit Quality during Postharvest Storage*

Visual assessment of postharvest fruit quality using variables such as bruises, dents, and mold incidence during postharvest storage indicated a 20% increase in the percentage of defective fruit from 1 day until 29 days after storage in Premier (Table 2). There were no significant effects of the PGR treatments until 29 days after harvest in Premier (Table 2). At 29 days after harvest, ABA application resulted in a higher proportion whereas ethephon application resulted in a lower proportion of defective fruit compared with the control. In Powderblue the percentage of defective fruit increased by 15% from 1 day until 29 days after storage in control fruit; none of the PGR applications significantly affected the visually assessed variables for fruit quality (Table 2).

In Premier, fruit compression and puncture declined in the control by 18 and 20%, respectively, at 29 days after storage compared with 1 day after storage (Table 3). In Premier, ABA applications reduced the force required for fruit compression at 29 days of postharvest storage by ~17%, suggesting a decrease in fruit firmness relative to the control (Table 3). None of the other treatments affected fruit texture characteristics or the other fruit quality characteristics such as fruit weight, TSS, TA, and juice pH, evaluated during postharvest storage with respect to the control (Tables 3 and 4). In Powderblue, fruit compression and puncture declined in the control by 17% and 26%, respectively, at 29 days after storage compared with 1 day after storage (Table 3). In Powderblue, fruit firmness as measured by compression was higher by 16% in ethephon-treated fruit compared with the control at 15 days of postharvest storage (Table 3). Fruit weight did not differ among various treatments during postharvest storage with respect to the control (Table 3). Ethephon treatment resulted in higher TA values than that in the control at various times after storage, although this was significant only at 15 days of postharvest storage (by 21%) (Table 4). TSS was lower in the ABA treatment than in the control at 15 days after harvest by ~11%. Also, juice pH was lower in response to ethephon and MeJA treatments than in the control at 1 day after harvest (Table 4).

**Table 2.** Percent defective fruit determined at various times after harvest in Premier and Powderblue blueberry following preharvest treatment with water (control), ethephon, abscisic acid (ABA), and methyl jasmonate (MeJA).


z Means followed by the same letter within a column for a given time-point after storage are not significantly different, according to Tukey's HSD (α = 0.05).

**Table 3.** Effect of preharvest treatment with water (control), ethephon, abscisic acid (ABA), and methyl jasmonate (MeJA) on fruit texture and weight sampled at 1, 15, and 29 days of cold storage at 4 ◦C in Premier and Powderblue blueberry.


z Means followed by the same letter within a column for a given time-point after storage are not significantly different, according to Tukey's HSD (α = 0.05).


**Table 4.** Effect of preharvest treatment with water (control), ethephon, abscisic acid (ABA), and methyl jasmonate (MeJA) on fruit quality sampled after 1, 15, and 29 days of cold storage at 4 ◦C in Premier and Powderblue blueberry.

z Means followed by the same letter within a column for a given time-point after storage are not significantly different, according to Tukey's HSD (α = 0.05).

#### *3.4. Effect of PGR Application on Postharvest Disease Incidence During Storage*

The major postharvest pathogens indicated by disease symptoms and signs in this study were *Colletotrichum acutatum* (causal agen<sup>t</sup> of anthracnose fruit rot), *Phomopsis vaccinii*, *Botrytis cinerea* (gray mold), *Alternaria* spp., and *Pestalotia* spp. Postharvest disease incidence in both Premier (typically < 5%) and Powderblue (typically < 10%) was low, despite the 4-day incubation period at room temperature following various postharvest storage periods. Due to low pathogen counts, only overall postharvest disease incidence was analyzed; no significant differences among treatments at different time intervals of storage were observed (Figure 2).

**Figure 2.** Percent postharvest disease incidence determined at various times after harvest in Premier (**A**) and Powderblue (**B**) rabbiteye blueberry following applications of water (control), ethephon, abscisic acid (ABA), and methyl jasmonate (MeJA). Values are means and standard errors of four replicates and 40 to 60 fruit per replicate. No significant differences (α = 0.05) were detected among the treatments.
