Dynamic controlled atmosphere (DCA) is a prominent technology used worldwide for long-term apple storage. In Washington, the adoption of DCA technologies to manage low oxygen levels is limited, partly because the benefits are not clearly demonstrated for some major cultivars, such as ‘Honeycrisp’ and new varieties like ‘WA 38’. The response of ‘Honeycrisp’, ‘Gala’, and ‘WA 38’ apples to lower oxygen levels was monitored monthly until 8 months of storage (1oC or 3oC) through chlorophyll fluorescence (CF) and respiratory quotient (RQ) by a stepwise decrease in O2 levels at each time point during 2023/2024 season. Ethanol and acetaldehyde concentrations were obtained from fruit juice before and after the lower oxygen limit (LOL) determinations. ‘Honeycrisp’ and ‘Gala’ apple cultivars showed differences in LOLs determined through CF or RQ. CF LOL for ‘Honeycrisp’ was approximately 0.3-0.2 kPa O2 compared to 0.1 kPa O2 for ‘Gala’ while RQ response occurred at 0.1 kPa O2 level in both cultivars. ‘WA 38’ apples displayed inconsistent CF responses at 0.3 and 0.4 kPa oxygen levels. Ethanol concentration increased after low oxygen stress irrespective of the cultivar. During the first month of storage and after the low oxygen stress, ‘Honeycrisp’ apples accumulated (in average) 120 ppm of ethanol, ‘Gala’ 2.92 ppm, and ‘WA 38’ 4.24 ppm. Towards the end of storage, the ethanol concentration showed an increase for ‘Gala’ (25 ppm), which was not observed for the other two cultivars. Small amounts of acetaldehyde were accumulated only in ‘Honeycrisp’ apples. This study highlights the different responses of apple cultivars to low oxygen stress during the lower oxygen limit (LOL) determination, with ‘Honeycrisp’ being the most sensitive one among the cultivars tested. Further seasons are needed to confirm these results and include the seasonal-dependent responses in each cultivar.
‘WA 38’ (Cosmic Crisp®) is the newest cultivar released by the Washington State University apple breeding program, and today in its sixth year of commercial production in WA. This cultivar has a high pack-out, i.e. highly colored fruit and few external and internal defects. Nevertheless, skin greasiness has been one of the main defects at harvest and postharvest, making waxing during packaging challenging, and affecting the cosmetic appearance. Since the starch degradation index is the only maturity index used to commercially harvest WA 38, the correlation between maturation and the onset of greasiness was studied during two seasons. Different maturity indices pre-and postharvest (firmness, soluble solid content, internal ethylene concentration (IEC), starch index (1-6), IAD values) along with skin greasiness were evaluated from 3-4 weeks before harvest (WBH) until 6 months in air (1oC) or controlled atmosphere (2.5 kPa O2, 1.5 kPa CO2) storage in fruit from four commercial orchards (#1 to #4; 2nd-4th-leaf). In 2022 and 2023 the rate of change of all maturity indices were block-dependent. In both years, IEC was detected in up to 80% of the fruit sampled four WBH in orchard #1 (average 0.3 ppm). At this same time point, only 16% of the fruit had started the starch degradation process (SI=1.5/6.0). The climacteric peak occurred 3-5 months into cold storage, and it was block-dependent. Greasiness on fruit skin was detected 2 WBH in two of the four orchards in 2022; in 2023 this occurred at commercial harvest. Overall, there was a higher incidence (and severity) of greasiness in fruit from air storage compared to CA, and in both cases, it increased during the shelf-life period (7 d at 20oC). The results indicate that fruit greasiness appears to be more related to fruit maturity and perhaps seasonal weather than tree age, nevertheless, additional seasons are needed to confirm these results.
‘Granny Smith’ is an important apple variety for Washington State, where it has consistently been ranked as the third most-produced conventional cultivar since 2017. This apple variety is highly susceptible to sunscald, a sun-stress-related postharvest disorder that typically appears after three months of cold storage and makes apples unmarketable. Previous research has shown that a decrease in chlorophyll (chl) and an increase in carotenoids (car) in fruit peel have been associated with increased sunlight exposure and the development of sunscald. In order to assess the use of the chl/car ratio measured non-destructively with a Vis/NIR hyperspectral imager as a predictive index for sun exposure and sunscald development postharvest, ‘Granny Smith’ apples were picked from the periphery and inner canopy sections of the tree in 2021 and 2023 seasons. Fruit position in the canopy was documented during sampling and later correlated with hyperspectral images, chlorophyll, and carotenoid content in the peel. Subsequently, the collected peel sample was immediately frozen with liquid nitrogen and stored at -80°C. The chl/car ratio obtained from the reflectance values from the hyperspectral images was well correlated (r2 = 0.82) with the destructive determination of the ratio. Based on k-means clustering analysis, samples were grouped in accordance with the chl/car ratio and associated with fruit position on the tree. Apples with the highest chl/car ratios (1.4 to 1.7) were those located on the shaded portion of the trees. Apples with sunburn had the lowest chl/car ratios (0.1 to 1.2) and were located on the periphery of the tree. The results indicate that the chlorophyll to carotenoid ratio measured non-destructively at harvest can potentially be used for pre-storage sorting of ‘Granny Smith’ apples based on relative sun exposure and sunscald susceptibility, reducing postharvest losses. However, the establishment of the index reliability can benefit from additional years of data collection.
‘Granny Smith’ apples are highly susceptible to skin browning (=scald). These disorders can significantly reduce fruit’s marketability due to their unattractive appearance. Superficial scald and sunscald have different etiologies but their symptoms are similar and easily mistaken. The oxidation of α-farnesene causes superficial scald (SS); on the other hand, sunscald (SC) is a non-oxidative process that affects only the sunlit sides of the fruit. To correlate the spectral fingerprint with fruit susceptibility to these disorders, hyperspectral images (400-1000 nm, 640x865 px; Headwall Photonics, Bolton, MA) were taken at harvest from sun-exposed and unexposed sides of the fruit (n=216; ~26,000 px) and later, after six months in air storage (33 oF), correlated with scald incidence. The dataset grouped 145 asymptomatic, 117 with SS and 170 with SC fruit. After pre-processing spectral information (Savitzky-Golay dev, standard normal variate), iPLS wavelength selection showed that bands from 400 to 650 and 900 to 950 nm were the most accurate for at-harvest spectral differentiation between superficial and sunscald symptoms. A neural network classification model was trained (18,226 px) and validated on an independent dataset (7,808 px), achieving overall accuracies of 78 % and 73 %, respectively. After prediction, SC px obtained the highest classification metrics (accuracy 87 %, precision 86 %); meanwhile, the asymptomatic class showed the lowest metrics (accuracy 74 %, precision 60 %). These preliminary results showed that in the same way, sunscald could be identified close to harvest using hyperspectral fingerprints, superficial scald could also be predicted at harvest on susceptible fruit and differentiated from sunscald susceptible fruit.
Dynamic controlled atmosphere (DCA) storage suppresses the ripening of apple fruit during storage to a greater extent than standard CA storage. DCA is a relatively new technology, and it has the potential to markedly alter the volatile profile of apple fruit. It has been found that DCA storage can suppress the most important aroma volatiles of stored apple fruit. What we don't know is the length of time and the conditions needed to recover that loss in aroma, especially when DCA is applied in combination with the ethylene action inhibitor 1-methylcyclopropene (1-MCP). A critical concern about 1-MCP is that apple flavor is compromised in treated fruit because aroma volatiles are so closely linked with ethylene response. Apple fruit from high-value cultivars were stored under a DCA regimen (approximately 0.4% O2), with and without 1-MCP treatment, for 3, 6, and 9 months. Following removal of fruit from DCA, the volatile profile and fruit quality traits were measured for up to 5 weeks while being held at room temperature. The recovery of aroma formation following storage for 6 months was essentially immediate for ‘Red Delicious’ fruit if 1-MCP was not used. The recovery was a little slower for one of the replicate studies if DCA was used. If the fruit were treated with 1-MCP, there was a 2-week delay in the recovery of aroma formation. ‘Evercrisp’ aroma formation was much lower than ‘Red Delicious’ and the responses to DCA and 1-MCP differed from that of Red Delicious. Aroma formation remained very low for 3 to 4 weeks at room temperature following CA and DCA storage and never recovered following 1-MCP treatment for the 5-week duration of the study. The data for aroma formation after 9 months was similar to that at the 6-month time point for ‘Red Delicious’ in terms of 1-MCP responses. However, the effect of DCA seemed to be more pronounced, suppressing aroma recovery for an additional week at room temperature. For ‘Evercrisp’, the 9-month data were quite similar to those from 6 months storage.
Dr. Randolph Beaudry, Professor, MSU Department of Horticulture (MSc, PhD, University of Georgia). His appointment is 50% MSU Extension and 50% AgBioResearch. His research program includes both regional and international projects and focuses on the physiology of plant responses to... Read More →
There has been a surge in demand for organic apples in the U.S. in the last decade. Washington State supplies more than 90% of them because of the ideal climate and soil conditions that favor production. Thermotherapy methods are widely used in Europe to reduce postharvest rots, but they have not been adopted in the U.S. because of their potential detrimental effects on fruit quality. The objective of this research was to evaluate the impact of hot water treatments at harvest on fruit quality during long-term storage. ‘Royal Gala’ and ‘Honeycrisp’ apples were immersed at 49 °C or 52 °C for 2 minutes in a controlled hot water bath immediately after harvest. After fruits were dried at 20 °C, they were placed in controlled atmosphere (CA; 2 kPa O2, 0.5 kPa CO2, 1°C-‘Royal Gala’, 3oC-‘Honeycrisp’) and air (RA; 1°C-‘Royal Gala’, 3oC-‘Honeycrisp’) storage for up to 9 months. Fruit quality (firmness and titratable acidity), defects, and physiological disorders were evaluated 1 and 7 days at 20 °C. In general, ‘Royal Gala’ apples immersed at 49 °C and stored in CA had no decay after 3 and 6 months of storage, but it was the highest (around 9%) in ‘Honeycrisp’ in both CA and RA. Peel damage was less at 49 °C for both ‘Royal Gala’ (RA-1.3%; CA-5%) and ‘Honeycrisp’ (RA-7.4%; CA-2.8%) compared to 52 °C after 3 months. Fruit firmness and titratable acidity were statistically different (p≤0.05) at 49 °C compared to 52 °C after 3 months. Although the hot water treatment in ‘Royal Gala’ apples was effective in reducing decay incidence without compromising fruit quality, the opposite was found in ‘Honeycrisp’; therefore, further research is needed to confirm these results and understand the variety-dependent effect.
I am a second-year Ph.D student at Washington State University (Tree Fruit Research & Extension Center). My research is about using non-chemical solutions for long-term storage of organic apples.
Recent studies have shown that the native microbiome plays an important role in biocontrol efficacy, but in comparison less is known about how the microbiome responds to conventional and natural product fungicides. This study investigated the effects of conventional fungicide fludioxonil, natural product fungicide natamycin, and scald inhibitor diphenylamine (DPA) on the microbiomes of ‘Fuji’ apples (Malus x domestica) from 1-28 days of cold storage and 7 days of room temperature after the cold storage. We hypothesized that fludioxonil would have a smaller effect on the microbiome than natamycin due to being more limited in targeting specific pathogens, and that antioxidant activity from DPA would shift the microbiome. DPA showed a strong effect on the fungal microbiome that increased with storage time, while natamycin resulted in modest fungal shifts and fludioxonil resulted in no observed shifts. While chemical treatment was not a predictor of bacterial microbiome variation, bacterial communities shifted throughout storage with many of the trends reversing when samples were removed and left at room temperature. Time in cold storage decreased the relative abundance of Pseudomonas and DPA application reduced the relative abundance of Aureobasidium, both notable biocontrol genera. These results highlight how chemical applications like DPA may have unintended effects on beneficial microbes that protect crops from pathogen infection.
Fruits constitute a critical part of a healthy diet. However, they often perish prior to consumption due to unpredictable ripening. Especially in climacteric fruit, blockage in the perception or synthesis of ethylene has been used to prolong shelf life. European pear (Pyrus communis) are classified as climacteric fruit. However, System 2 ethylene production requires a genetically pre-determined period of cold conditioning, which triggers ripening—in addition, applying 1-MCP, an ethylene perception inhibitor, indefinitely blocks ripening. Using a physiological and developmental transcriptomics approach, we have shown that in 1-MCP fruit stored in a controlled atmosphere, activating alternative respiration via glyoxylic acid stimulation of AOX expression can reverse the effect of 1-MCP. Interestingly, 1-MCP fruit without CA storage responds differently to glyoxylic acid. It shows classic signs of senescence. The underlying processes of ripening and senescence can be discerned by utilizing the fruit that has been treated differently post-1-MCP application. This knowledge is expected to aid in identifying strategies to prolong fruit shelf life.
Head of the Department of Horticultural Sciences, Texas A&M University
Dr. Amit Dhingra is the Head of the Department of Horticultural Sciences, Professor of Genomics and Biotechnology, and Senior Scientist at the Norman Borlaug Institute for International Agriculture at Texas A&M University. After his post-doctoral training at Rutgers University, the... Read More →
Phytopathogenic fungi can cause rots during cold storage leading to the loss of pear fruit and significant economic costs. Currently, all commercially available pear varieties are susceptible to postharvest rots. Genetic resistance to fruit rot pathogens including Penicillium expansum and Colletotrichum spp. has been identified in wild apple germplasm. The objective of this study was to evaluate diverse genotypes of European pears (Pyrus communis L.) for disease incidence during cold storage and evaluate susceptibility to prevalent phytopathogenic fungi by directly challenging fruit using a wound inoculation method. Fruit from 38 pear genotypes were harvested at maturity, then evaluated weekly for the presence of postharvest rots during cold storage. If rot was observed, the diseased fruits were removed from cold storage and fungal isolates were collected from fruit with disease symptoms. The identity of fungal isolates was determined based on morphology and genetic sequencing of marker genes including ITS and TEF1. After 12 weeks in cold storage, the incidence of rot ranged from 8.3% to 100%. Colletotrichum was the most prevalent genus isolated from the rotting pears. Twenty pear genotypes were directly challenged with P. expansum or C. fioriniae using a wound inoculation method on fruit that was harvested at commercial maturity. Five genotypes had significantly reduced disease development when challenged with P. expansum compared to susceptible varieties Gem and Bartlett. Four of these five genotypes also had significantly reduced disease development when challenged with C. fioriniae. One additional genotype was found to have significantly reduced disease development when challenged with C. fioriniae but was highly susceptible to P. expansum. These results will be a valuable resource for pear breeders and aid efforts to develop European pear varieties that have genetic resistance to fruit rot pathogens.
During his Ph.D. studies, Dr. Gottschalk studied the molecular mechanisms that control flowering in apple as they relate to seasonal bloom times and biennial/alternate bearing in diverse apple germplasm, from wild species to cultivated varieties. Moreover, he investigated plant growth... Read More →
