of heat damage can develop in <2 h when berry surface temperature exceeds 42 to 48 °C. Necrosis occurs in both immature and ripe berries and usually starts with distinct browning or reddish spots that eventually collapse within a few days. When
In an effort to develop an inexpensive alternative to vapor-heat insect disinfestation of `Kensington' mango (Mangifera indica Linn.), the effect of postharvest hot water treatments (HWT) on fruit quality was determined. Fruit were given 46C HWT for 30 minutes at a fruit core temperature of 45C either 24 hours after harvest or after various conditioning treatments of 4 to 24 hours at 39 ± 1C in air. Fruit were compared to nontreated fruit after a subsequent 7 days at 22C. The HWT increased fruit softening and reduced chlorophyll fluorescence and disease incidence. The longer conditioning times produced softer fruit. Conditioning reduced damage to the fruit caused by HWT. Preconditioning for ≥8 hours resulted in <1% of fruit being damaged as shown by cavities, skin scald, and starch layer formation. The quantitatively measured higher mesocarp starch content paralleled the visible starch layer injury. Skin yellowing increased in response to HWTs that were not damaging to the fruit. Fruit ripening changes were unequally affected by HWT and by conditioning before HWT; thus, the sequence and extent of these changes must be determined to establish a reliable and useful hot water disinfestation treatment.
Blossom thinning can confer significant benefits to apple growers, including increased fruit size and annual bearing. However, current blossom thinning practices can damage spur leaves and/or fruit. We evaluated the use of short duration forced heated air treatments [thermal shock (TS)] as a blossom thinning strategy for ‘York Imperial’. Using a variable-temperature heat gun, TS treatments were applied to solitary blossoms 24 hours after pollination. Effects of output temperature (five levels) and treatment duration (four levels) were evaluated using a completely randomized design with a factorial treatment structure. Short duration treatments (0.5 and 1.0 seconds) were ineffective for arresting pollen tube growth in vivo. TS temperature required to inhibit stylar pollen tube growth was inconsistent across years. In 2014, TS temperatures ≥56 °C inhibited pollen tubes from reaching the style base at 2.0 and 4.0 second durations. However, in 2015, TS temperatures ≥81 °C at 4.0 seconds prevented pollen tubes from reaching the style base. Inconsistent effects of TS across years were attributed to treatments being applied too late due to optimal conditions for pollen tube growth during the intervening 24-hour period after pollination. Excessive injury to spur leaf tissue was observed at temperatures higher than 84 °C and 70 °C (2.0 and 4.0 seconds, respectively). Pollen tube growth was reduced or arrested at temperature and duration combinations that caused minimal visible injury to spur leaves. Identifying and exploiting structural differences between apple blossoms and vegetative spur leaves may provide insight for the future development of TS or other attempts at developing selective thinning technologies.
The use of short-duration applications of thermal energy (thermal shock; TS) as an apple blossom thinning strategy was investigated. Effects of TS temperature and timing on stigmatic receptivity, pollen tube growth in vivo, and visible leaf injury were evaluated in multiple experiments on ‘Crimson Gala’. TS treatments were applied to blossoms and spur leaves using a variable temperature heat gun. TS temperatures ≥86 °C had a strong inhibitory effect on pollen tube growth on the stigmatic surface and in the style. TS temperatures >79 °C reduced average pollen tube length to less than the average style length. Timing of TS treatment (0 or 24 hours after pollination) was not an influential factor, indicating that effective TS temperatures reduced pollen tube growth up to 24 hours after the pollination event. The onset of thermal injury to vegetative tissues occurred at similar TS temperatures that inhibited pollen tube growth in vivo. Excessive leaf injury (>33%) was observed at 95 °C, suggesting relatively narrow differences in thermal sensitivity between reproductive and vegetative tissues. Inconsistent TS temperatures and/or responses were observed in some experiments. Ambient air temperature may have influenced heat gun output temperatures and/or plant susceptibility. While results suggest some promise, additional work is required to validate and further develop this concept.
Crop loss from heat damage is becoming a prevalent problem for many blueberry growers in the northwestern United States. The region, which includes Oregon and Washington, is the leading producer of blueberries in the country [ U.S. Department of
is the risk of heat damage critical economically in blueberries, and how can cooling practices be optimized to prevent the damage efficiently? Previously, Yang et al. (2019) found that visual signs of heat damage occur in northern highbush blueberry
Three successive experiments were included in this trial. The first experiment was a derailed screening program to test the effects of various temperatures and durations on the fruit quality of strawberry fruit. Fruit were exposed to temperatures of 37, 40, 43, and 46°C for durations of 20, 40, 60, 80, end 100 minutes at each temperature level. The temperatures and durations which were detrimental to fruit quality were eliminated; then experiments 2 & 3 were conducted using the remaining temperature and duration levels to study their effects on fruit quality, respiration, and ethylene production.
Strawberries heated to 46° C were too severely damaged for other test comparisons. Those exposed to temperature treatments of 43 °C for 30 or 60 mins were consistently less firm, had more heat damage, developed less decay, and had lower CO2 and ethylene production than fruit from lower temperature treatments or control fruit. Differences were sometimes significant.
While the heat damage scores from fruit exposed to the 43°C treatments indicated some serious injury, the fruit were stiff judged to be marketable. There were no significant differences in soluble solids content (SSC), titratable acidity, SSC/acid ratio, or juice pH among any of the treatments.
Three successive experiments were included in this trial. The first experiment was a derailed screening program to test the effects of various temperatures and durations on the fruit quality of strawberry fruit. Fruit were exposed to temperatures of 37, 40, 43, and 46°C for durations of 20, 40, 60, 80, end 100 minutes at each temperature level. The temperatures and durations which were detrimental to fruit quality were eliminated; then experiments 2 & 3 were conducted using the remaining temperature and duration levels to study their effects on fruit quality, respiration, and ethylene production.
Strawberries heated to 46° C were too severely damaged for other test comparisons. Those exposed to temperature treatments of 43 °C for 30 or 60 mins were consistently less firm, had more heat damage, developed less decay, and had lower CO2 and ethylene production than fruit from lower temperature treatments or control fruit. Differences were sometimes significant.
While the heat damage scores from fruit exposed to the 43°C treatments indicated some serious injury, the fruit were stiff judged to be marketable. There were no significant differences in soluble solids content (SSC), titratable acidity, SSC/acid ratio, or juice pH among any of the treatments.
Longitudinal halves of freshly harvested avocado fruit (Persea americana Mill. `Hass') were pretreated at 38C for 1 hour in a water bath, while the other half remained at 20C in air. Then the entire fruit was either treated from 1 to 10 minute at 50C, or held at 20C (controls). Fruit quality (daily evaluation of browning and internal quality when ripe), and pulse amplitude modulated (PAM) fluorescence measurements, were made on the skin of each fruit half 1 hour after hot water treatment (HWT), 3 hours later, and each subsequent day until ripening. The pretreated half of the fruit showed almost no development of external browning during the ripening period, while the nonpretreated halves were severely damaged by HWTs. External browning increased with longer HWT duration. Heat damage was also evident as hardening of the skin when fruit ripened, and such damage was reduced by pretreatment and increased with longer HWT duration. HWT had a rapid and marked effect on chlorophyll fluorescence (Fv/FM ratio) of avocado skin. Whereas fluorescence of control fruit remained constant over the first 5 days, in both pretreated and nonpretreated fruit, within 1 hour of HWT, the Fv/FM ratio had dropped to near minimal levels, with little further change. The value of Fv/FM 3 to 6 hours after the HWT was directly related to the duration of the HWT (P <0.0001). Although pretreatment almost eliminated browning, little effect of pretreatment could be detected in the Fv/FM ratio. There was a strong negative correlation (r = 0.93, P < 0.0001) between external browning and Fv/FM for nonpretreated fruit, but this correlation was not significant for pretreated fruit. We conclude that chlorophyll fluorescence clearly reflects effects of heat on the photosynthetic systems in avocado fruit, but does not detect the alleviation of heat damage by pretreatments.