Apple Sunburn Research Articles

Efficacy evaluation of apple sunburn mitigation techniques in WA 38 cultivar using crop physiology sensing system

This study evaluated the efficacy of two heat stress mitigation techniques, i.e., modified evaporative cooling (EC), and drape/shade net (SN) against untreated control (UC) in terms of fruit surface temperature (FST) suppression and internal fruit quality for cv. WA 38. The EC treatment used foggers (flow rate: 4.1 L s−1 ha−1) spaced at 3.3 m along the row to create mist within the canopy. The experiment was conducted in a 0.2 acre block planted on two randomly distributed rootstocks [Geneva 41 (G41) and Malling 9-Nic 29 (M9)], trained in a bi-axis vertical wall architecture. Treatments were divided into three sub-blocks. Alternate wet and dry zones were observed in the sub-block treated with fogger-based EC and was therefore subdivided into EC-Wet and EC-Dry treatments. The proximal thermal-RGB imaging and in-field weather sensing integrated crop physiology sensing system (CPS2.0) was upgraded with edge computing capability to monitor real-time apple FST, an indicator of heat stress. Deployed nodes monitored imagery and weather data based FST in each treatment at an interval of 5-min throughout the growing season (i.e., during fruit maturation). Aerial imagery-based canopy temperature mapping with ground sampling distance of 4 cm/pixel was also utilized to monitor the canopy heat stress at key growth stages. CPS2.0 imagery derived apple FST was effectively reduced by EC-Wet (G41: 27.1 ± 0.4 and M9: 28.8 ± 0.4 °C) (mean ± std. error) and SN (G41: 29.8 ± 0.2 and M9: 30.5 ± 0.1 °C) treatments compared to the UC (G41: 33.1 ± 0.2 and M9: 31.4 ± 0.4 °C) throughout the production season. However, convective cooling from EC-Dry (G41: 33.1 ± 0.2 and M9: 32.5 ± 0.2 °C) treatment failed to mitigate heat stress. Results suggest that fogger spacing, and orientation need adjustments along tree-rows for effective sunburn management. Overall, canopy temperature quantified by aerial imagery was significantly lower under modified EC (30.3 ± 1.3 °C) than UC (34.2 ± 1.3 °C) treatment. Compared to UC, EC-Wet and SN protection enhanced fruit quality with higher or similar crop load, fruit firmness, and quality.

Mask R-CNN aided fruit surface temperature monitoring algorithm with edge compute enabled internet of things system for automated apple heat stress management

Our prior study focused on development of internet of things (IoT) and edge-compute enabled crop physiology sensing system (CPSS) for apple sunburn monitoring. Edge compute algorithm on CPSS estimated sunburn susceptibility as fruit surface temperature (FST) through pixel-by-pixel multiplication of captured thermal infrared images with segmented fruits binary mask. The segmentation was performed using color-based K means clustering approach. This limited CPSS applicability to monitor sunburn of red colored cultivars only and when fruits develop color, typically late growing season. This is a key research gap as recent weather patterns have shown that sunburn can occur during early growing season when fruits are green to yellow. Therefore, aim of this study was to develop and field evaluate cultivar and color independent mask region-convolution neural network (R-CNN) aided fruit segmentation model and edge compute compatible FST estimation algorithm. Season long field data were collected in 2021 using eight CPSS nodes (three in cv. WA38 [Cosmic crisp] and five in cv. Honeycrisp). Collected data were used to develop and validate mask R-CNN based fruit segmentation model. Developed mask R-CNN based model was able to segment fruits of two apple cultivars and of varying colors with 91.4 % average precision. In orchard evaluations (2022 season), the resulting algorithm ported on CPSS was able to accurately segment (dice similarity coefficient = 0.89) and estimate apple FST with < 0.5 °C error compared to ground truth data. With compute time of about 37 s, data processing time was reduced by 22 % over previous algorithm. High ambient temperature (>35 °C) on a warmer day resulted in multiple throttling errors caused by excessive CPU temperature; however, the CPSS performance was uncompromised in FST estimation. Ambient air temperature did not affect RAM utilization and CPU clock frequency. Overall, developed FST algorithm can potentially be used as input to actuate water-based cooling system.

Retractable Netting and Evaporative Cooling for Sunburn Control and Increasing Red Color for ‘Honeycrisp’ Apple

Protective netting and evaporative cooling are commonly used for sunburn protection in apple (Malus domestica Borkh.) orchards in semiarid environments such as central Washington state. Sunburn is caused by a combination of solar radiation and heat, which can cause significant economic losses. Although protective netting and evaporative cooling can be effective for preventing apple sunburn, netting can also introduce new risks, including red color development on the fruit surface. This study evaluated whether retracting netting before harvest improves red color development and/or changes sunburn risk compared with leaving netting in place until after harvest. An experiment was conducted that compared three netting treatments: 1) netting from June until harvest, 2) netting retracted 10 d before harvest, and 3) no netting all season combined with the presence or absence of evaporative cooling. Fruit was harvested and assessed for sunburn incidence and external quality characteristics immediately after harvest. In retracted netting treatments, red color was higher when netting was retracted compared with the nonretracted controls, and sunburn risk did not increase with netting retraction. Evaporative cooling reduced sunburn incidence. Retractable netting can be used to minimize the loss of fruit to sunburn while allowing a full light environment that promotes red color near harvest. There is no inherent increase in sunburn risk from netting retraction, and the proportion of fruit with red color improved.

Climatic and physiological parameters related to the progress and prediction of apple sunburn damage in a neotropical climate

Climatic and physiological parameters related to the progress and prediction of apple sunburn damage in a neotropical climate

In-field crop physiology sensing aided real-time apple fruit surface temperature monitoring for sunburn prediction

Heat and light-instigated abiotic stresses during summer can cause several physiological disorders in perennial specialty crops. Such stressors increase the fruit surface temperature (FST) and prolonged exposure above a critical FST can result in sunburn. Sunburn in apple may cause considerable crop loss and reduce fresh produce marketability. Existing approaches for sunburn prediction and management, based on atmospheric temperature data, are often unreliable and inefficient for timely actuation of remedial measures. Therefore, this study focuses on the development of a non-invasive and real-time sunburn monitoring tool. We developed a crop physiology sensing (CPS) unit that uses visible-infrared imagery and in-field weather data for FST monitoring, the prime indicator of sunburn susceptibility. The CPS unit consists of a thermal-red-green-blue and all-in-one weather sensor integrated with a single-board computer. Acquired imagery data was analyzed in real-time using a custom-developed algorithm in python ‘OpenCV’ library to estimate imager-based FST. The algorithm was optimized for processing the data on a single-board computer with limited computational resources. Moreover, the processing unit was configured to acquire in-field weather data and to utilize a temperature dynamics weather model for weather-based FST estimation. Two automated CPS units were deployed in the commercial orchards of cv ‘Honeycrisp’ and ‘Cosmic Crisp™’ during the 2019 production season. For each cultivar, field data was collected for three days between 12 and 5 pm at 5-minute intervals. A contact type thermal probe of accuracy ±0.4 °C was also utilized for ground truth apple FST (FSTa) measurements. Furthermore, imagery data was analyzed to derive mean FST (FSTi), maximum FST (FSTi-max), and mean FST of the 10%, 15% and 20% hottest part of the fruit surface (i.e. FST10, FST15, and FST20, respectively). The results showed significant differences between FSTi, FSTi-max, FST10, FST15, and FST20 for Honeycrisp (F4,162 = 73.4, p < 0.0001) as well as Cosmic Crisp (F4,46 = 19.4, p < 0.0001) cultivars. Moreover, no significant difference was recorded between FSTi and FSTa. The weather model-predicted FST (FSTw) was found to be highly sensitive to fruit shading and a significant difference was recorded between FSTw and FSTi. Overall, the developed CPS unit demonstrates a promising potential for reliable FST monitoring that could aid growers in real-time apple sunburn susceptibility prediction and actuation of sunburn preventive strategies.

Robust image processing algorithm for computational resource limited smart apple sunburn sensing system

Heat and light stress causes sunburn to the maturing apple fruits and results in crop production and quality losses. Typically, when the fruit surface temperature (FST) rises above critical limits for a prolonged duration, the fruit may suffer several physiological disorders including sunburn. To manage apple sunburn, monitoring FST is critical and our group at Washington State University is developing a noncontact smart sensing system that integrates thermal infrared and visible imaging sensors for real time FST monitoring. Pertinent system needs to perform in-field imagery data analysis onboard a single board computer with processing unit that has limited computational resources. Therefore, key objective of this study was to develop a novel image processing algorithm optimized to use available resources of a single board computer. Algorithm logic flow includes color space transformation, k-means++ classification and morphological operators prior to fruit segmentation and FST estimation. The developed algorithm demonstrated the segmentation accuracy of 57.78% (missing error = 12.09% and segmentation error = 0.13%). This aided successful apple FST estimation that was 10–18 °C warmer than ambient air temperature. Moreover, algorithm reduced the imagery data processing time cost of the smart sensing system from 87 s to 44 s using image compression approach.

Thermal-RGB imager derived in-field apple surface temperature estimates for sunburn management

Apple sunburn is a major challenge for the apple growers and so is its prediction for taking timely remedial measures. In this study, a thermal-RGB imager was developed and evaluated to estimate the real-time fruit surface temperature (FST) of an apple. The thermal-RGB images were captured for two apple varieties namely Golden Delicious and Red Delicious. Custom image processing algorithms were developed to estimate the FST from captured data. Two sets of experiments (1 and 2) were conducted on day-1 and -2, respectively. In experiment-1, the thermal-RGB imager estimated a maximum FST of 42.24 °C for Golden Delicious and 43.85 °C for the Red Delicious cultivar. Similarly, in experiment-2, the thermal-RGB imager estimated a maximum FST of 40.51 °C for Golden Delicious and 43.81 °C for the Red Delicious cultivar. The overall standard error for FST estimation from thermal-RGB imager ranged within 0.12–0.23 °C. The FST estimates from thermal-RGB imager were compared with the FST estimates from high resolution (pixel size = 0.17 μm) thermal imager (coefficient of determination, R2 = 0.80–0.90, root mean square error, RMSE = 0.50–1.08 °C and Pearson correlation coefficient, r = 0.90–0.95) and micro-climate sensor data (R2 = 0.87–0.90, RMSE = 0.98–1.97 °C and r = 0.92–0.99). Overall, the thermal-RGB imager was found to be an accurate estimator of apple FST (standard error = 0.12–0.23 °C). The thermal-RGB imager was advantageous in apple segmentation based on RGB imaging integrated with thermal imaging. The thermal imaging principle of capturing infrared radiations, irrespective of the unsteady weather parameters accounted for all types of heat flows occurring on the apple surface. Imager estimated the critical conditions for apple sunburn with numerous advantages over other techniques and can further ease out the formation of decision support system for apple sunburn management.

Ineffectiveness of foliar S-ABA application as an apple sunburn suppressant explained through effects on peel biochemistry and leaf ecophysiology

Abstract Sunburn is a physiological disorder that affects the visual quality of apple (Malus Domestica) fruit. In South Africa, producers estimate yield losses of up to 50% in green cultivars due to sunburn damage. Recent research in Japan has found that foliar application of abscisic acid (S-ABA) reduced sunburn in apples by up to 30%. The aim of this study was to examine the effect of S-ABA application on the occurrence of sunburn and on other fruit quality parameters in ‘Granny Smith’, the apple cultivar that suffers most sunburn under South African conditions. Trials were conducted over three growing seasons from 2010–2011 to 2012–2013 in a ‘Granny Smith’ orchard in Grabouw, South Africa. S-ABA was applied at concentrations between 250 and 1000 ppm and various timings during summer (from November until harvest in March/April). A representative scaffold branch on both sides of the tree was strip picked at commercial harvest resulting in samples of at least 100 fruit per tree for sunburn, fruit color, and red blush assessment. A sub-sample of 20 fruit was randomly selected and used to determine average fruit size, fruit firmness, and internal quality. The application of S-ABA did not decrease sunburn incidence and severity under South African growing conditions. S-ABA application decreased the peel concentration of total antioxidants, total phenolics and reduced ascorbic acid whilst increasing oxidized ascorbic acid. These changes suggest that S-ABA either downregulated synthesis of antioxidants or caused increased oxidative stress. Consistent with S-ABA application possibly causing stress, leaf necrosis was observed when S-ABA was applied just prior to periods of high temperature. Consistent with its physiological role in plants, S-ABA application decreased stomatal conductance and thereby also decreased the net carbon assimilation and transpiration rates, while the stem water potential was increased due to reduced water loss. Concomitant with the decrease in carbon assimilation, there was a significant reduction in total soluble solids, and titratable acidity with repeated S-ABA applications. S-ABA did not affect fruit maturity. Our results suggest that application of S-ABA to reduce sunburn is ineffective under South African conditions and therefore not recommended.

Above and below-ground environmental changes associated with the use of photoselective protective netting to reduce sunburn in apple

Anti-hail (protective) netting was originally developed to protect horticultural crops from hail damage. Netting reduces the amount and modifies the light reaching the orchard canopy. It also has the potential to optimize conditions for canopy and fruit growth and mitigate abiotic stress as climate change leads to increased temperatures. This study measured the effect of different colors of netting on the above and below-ground environment and apple sunburn incidence in a 3-year-old ‘Honeycrisp’ apple orchard growing in an irrigated desert climate in comparison to a traditional uncovered control. Netting did not affect air temperature or relative humidity within the orchard canopy, but reduced wind speed by 40% compared to the uncovered control. Netting reduced soil temperature and improved soil moisture at 20 and 40cm depths throughout the study period compared to the uncovered control. Amongst different colors of netting tested in this study, pearl and blue netting significantly reduced soil temperature compared to red netting. Netting also reduced photosynthetically active radiation (PAR) by approximately 20% and strongly reduced fruit surface temperature during hot periods. During full sunlight, differences in maximum fruit surface temperature between the uncovered control and the protective netting were 2.6–4.3°C under full sun conditions and reduced the incidence and severity of sunburn measured at harvest. As temperatures warm in the future, netting provides a viable option to mitigate some of the negative effects of excessive temperature and light on apple production in hot, dry growing regions.

Identifying fruit characteristics for non-invasive detection of sunburn in apple

Sunburn of apple fruit is one of the major problems in fruit production areas with high light and temperature environment. Fruit with sunburn are predisposed to develop postharvest disorders and need to be separated from the fruit considered for mid to long-term storage. In order to identify specific characteristics for non-invasive, automatic selection of fruit with sunburn, the effect of sunburn on external and internal features on sunlit and shaded fruit sides was assessed in ‘Granny Smith’, ‘Fuji’ and ‘Braeburn’ cultivars. It has been shown that shaded sides of apple with and without sunburn generally do not differ in their internal fruit quality characteristics, L ab colour readings and chlorophyll fluorescence intensities. With sunlit fruit sides, sunburn induced changes in L ab values are cultivar specific. The common feature of fruit with sunburn in all tested cultivars is a greater difference between fruit firmness and soluble solids content on shaded and sunlit sides as compared to unaffected fruit. Due to the chlorophyll breakdown in the affected areas, laser-induced chlorophyll fluorescence (LIF) is proposed as an appropriate sensitive technique for the reliable sunburn detection in green and red apple cultivars.

Photooxidative Sunburn of Apples: Characterization of a Third Type of Apple Sunburn

ABSTRACT Photooxidative sunburn, a third type that is distinctly different from sunburn necrosis and sunburn browning, is described for apple (Malus domestica Borkh.). Shaded (nonacclimated) apples suddenly exposed to sunlight became photobleached and eventually necrotic. Electron micrographs and electrolyte leakage studies indicated that cell death occurred with photobleaching. Photobleaching occurred at fruit surface temperatures (FST) below 31°C. Sunburn browning and sunburn necrosis require FST above 45°C. Ultraviolet-B radiation is involved in induction of sunburn browning, but blocking UV-A and UV-B radiation did not protect nonacclimated apples from photobleaching and necrosis. Infrared radiation (>700 nm) was ruled out as an induction factor. We suggest that visible radiation and the production of reactive oxygen species are the induction factors for photooxidative sunburn.

Application of Reflectance Spectroscopy in `Fuji' Apple Sunburn Early Detection

Sunburn can be caused either by heat stress or by UV-B radiation. Under natural conditions fruit sunburn is usually caused by the combination of both heat stress and UV-B radiation. To evaluate the use of reflectance spectroscopy in early detection of fruit sunburn, 5-year-old `Fuji' apple bearing trees growing in pot-in-pot system at the Lewis-Brown Horticulture Farm of Oregon State Univ. were used in the experiment. Fruit sunburn was monitored either under natural conditions or treated with UV-B, heat or both under controlled conditions after detached from the tree. Under natural conditions, the sun-exposed side of Fuji fruit has much higher anthocyanins than the shaded side. The increase in anthocyanins at the sun-exposed side is to protect the fruit from sunburn. When the temperature higher than 40 °C the sunburn symptom initiated first by change the color of the sun-exposed side from red to tan, then to yellow patches, and finally turn to brown and dark brown patches. The peel pigments analysis results indicated that anthocyanins decreased earlier than chlorophyll in the symptom development. The results of detached fruit exposure to 30,000μW/cm2 UV-B lights or to 40 °C at control conditions for 2, 4, 6, 8, 10, and 12 hours indicated that high intensity UV-B lights or high temperature alone can cause sunburn respectively. The UV-B and temperature combination treatment enhanced the sunburn processes. The apples with sunburn caused under natural conditions or under UV-B and temperature controlled conditions were scanned by using reflectance spectroscopy of FOSS NIR system at different stage of the sunburn. The results indicted that Fuji apple sunburn can be efficiently detected at the early stage of sunburn in both natural and controlled conditions.

ENVIRONMENTAL STRESSES THAT CAUSE SUNBURN OF APPLE

ENVIRONMENTAL STRESSES THAT CAUSE SUNBURN OF APPLE

Two Types of Sunburn in Apple Caused by High Fruit Surface (Peel) Temperature

Sunburn of apple costs growers millions of dollars in economic losses annually. We have identified two types of sunburn in apple and their causes. The first (sunburn necrosis) is caused by thermal death of epidermal and subepidermal cells (peel), and causes a necrotic spot on the sun-exposed side of the fruit. Thermal death occurs at 126 ± 2°F (52 ± 1°C). Electrolyte leakage increases significantly with necrosis, indicating that membrane integrity is lost during thermal death. The second type (sunburn browning) is sublethal and results in a yellow, bronze, or brown spot on the sun-exposed side of the fruit. Sunburn browning occurs at a fruit surface temperature of 115 to 120°F (46 to 49°C) and has little effect on membrane integrity, but sunlight is required for sunburn browning.Accepted for publication 24 September 2001. Published 4 October 2001.

Weather conditions associated with apple production in the Okanagan Valley of British Columbia

An analytical method that generates χ2 indices of association was used to determine the "critical" levels of daily weather occurrences associated with annual variations in apple production (Malus domestica Borkh.) in the Okanagan Valley of British Columbia over a 72-yr period, 1920–1991. The weather was recorded in the centre of the region (the Pacific Agri-Food Research Centre, Summerland). High temperatures during flower bud initiation in June (≥30 °C) and during flower bud development in August (≥26 °C) were associated with poor production the following year. Low temperature during November, December and February (critical value range, ≤ −7 °C to ≤ −29 °C) was the main climatic factor limiting apple production. These time periods correspond to the occurence of historical winter injury events. Daytime temperatures ≥5 °C at times during January also affects apple production adversely, probably because warm weather leads to tree deacclimation. Daily precipitation in March (≥1.0 mm) was associated with good production years which may indicate a requirement for early irrigation. Production was favoured by mild temperatures during bloom (≥21 °C daytime, ≥11 °C nighttime) and adversely affected by both very low temperatures (≤10 °C nighttime) and unseasonably high temperatures (≥28 °C daytime) coinciding with the temperature requirements of pollination and pollen tube growth. Good production years were also associated with a lack of low nighttime temperature (≤5 °C) in spring, probably associated with frost in low lying areas. Hot, dry weather during August of the harvest year (≥33 °C daytime, ≤2 mm) had a negative impact on apple production possibly because of loss in net photosynthesis, lower fruit size or apple sunburn. Warm weather during harvest (≥17 °C daytime) favoured production, probably because of improved conditions for harvest operations and low fruit losses from autumn frosts. Key words: Malus domestica Borkh., tree fruit, climate, heat stress, spring frost, winter injury

REDUCTION OF APPLE SUNBURN WITH CELLULOSE FIBERS

Reduction of heat stress disorders of `Golden Delicious' apples, such as sunburn, has been accomplished with cellulose fibers that modify reflective fruit surface properties. Incidence of sunburn on apples, directly exposed to sunlight, was decreased from 38% for untreated fruit to 12.5% for apples treated with cellulose fibers and binding agent and to 25.1% for apples treated with the binding agent only. Field stability of the binding agent (1% colloidal suspension of corn starch) was improved over the formulation used during the previous growing season. It was found that heating the starch suspension to 121C for 15 minutes increased its stability as a binding agent. A cumulative total of 3 cm (over three events) removed enough fibers to necessitate reapplication of the reflectant. The cellulose fiber/binder residue remaining at harvest was readily removed from fruit surface with water and a brush. Specialized sprayer was developed to deliver long fiber cellulose formulations that conventional sprayers are not capable of dispensing.