Soft scald is a common physiological disorder in ‘Honeycrisp’ apples that develops during cold storage and reduces fruit quality and marketability. Delayed cooling prior to cold storage and dynamic management of fruit storage temperature have been used to mitigate the development of soft scald with variable success. To explore biochemical changes associated with the development of soft scald and to identify mechanisms by which delayed cooling reduces its development, we conducted an untargeted metabolomics with data independent acquisition (DIA) on a liquid chromatography-mass spectrometry. Changes in ‘Honeycrisp’ apple metabolites were investigated during storage and in response to delayed cooling for two seasons. In total, 1212 features were detected and quantified. An ANOVA revealed significant changes in 114 metabolites at the metabolomic level. An ANOVA and orthogonal PLS-DA combined approach further showed 8 and 20 features changed significantly in association with development of soft scald features and in relationship to the delayed cooling treatment, respectively. Fifteen of these features were putatively identified indicating their role in soft scald development and mitigation. A group of flavonol compounds including isoquercitrin and rutin that increased during delayed cooling treatment were identified providing evidence that they may contribute to alleviate the disorder development. This study provides new evidence that metabolites associated with phenolic metabolism are involved in relation to soft scald disorder development and respond to delayed cooling treatment.

Plant diseases and pests reduce crop yields, accounting for global crop losses of 30% to 50%. In conventional agricultural production systems, these losses are typically controlled by applying chemical pesticides. However, public pressure is mounting to curtail agrochemical use. In this context, employing beneficial endophytic microorganisms is an increasingly attractive alternative to the use of conventional chemical pesticides in agriculture. A multitude of fungal endophytes are naturally present in plants, producing enzymes, small peptides, and secondary metabolites due to their bioactivity, which can protect hosts from pathogens, pests, and abiotic stresses. The use of beneficial endophytic microorganisms in agriculture is an increasingly attractive alternative to conventional pesticides. The aim of this study was to characterize fungal endophytes isolated from apparently healthy, feral wine grapes in eastern Canada that have grown without agrochemical inputs for decades. Host plants ranged from unknown seedlings to long-lost cultivars not widely propagated since the 1800s. HPLC-MS was used to identify unique endophyte-derived chemical compounds in the host plants, while dual-culture competition assays showed a range in endophytes’ ability to suppress the mycelial growth of Botrytis, which is typically controlled in viticulture with pesticides. Twelve of the most promising fungal endophytes isolated were identified using multilocus sequencing and morphology, while DNA barcoding was employed to identify some of their host vines. These fungal endophyte isolates, which consisted of both known and putative novel strains, belonged to seven genera in six families and five orders of Ascomycota. Exploring the fungal endophytes in these specimens may yield clues to the vines’ survival and lead to the discovery of novel biocontrol agents.

Summary Accurate and real-time monitoring of grapevine freezing tolerance is crucial for the sustainability of the grape industry in cool climate viticultural regions. However, on-site data is limited. Current prediction models underperform under diverse climate conditions, which limits the large-scale deployment of these methods. We combined grapevine freezing tolerance data from multiple regions in North America and generated a predictive model based on hourly temperature-derived features and cultivar features using AutoGluon, an automatic machine learning engine. Feature importance was quantified by AutoGluon and SHAP value. The final model was evaluated and compared with previous models for its performance under different climate conditions. The final model achieved an overall 1.36 °C root-mean-square error during model testing and outperformed two previous models using three test cultivars at all testing regions. Two feature importance quantification methods identified five shared essential features. Detailed analysis of the features indicates that the model might have adequately extracted some biological mechanisms during training. The final model, named NYUS.2, was deployed along with two previous models as an R shiny-based application in the 2022-2023 dormancy season, enabling large-scale and real-time simulation of grapevine freezing tolerance in North America for the first time.

Valdensia leaf spot, caused by Valdensia heterodoxa, is a serious disease of lowbush blueberry. The disease may develop rapidly, resulting in extensive defoliation of fields. The purpose of this study was to examine the effects of temperature and wetness duration on various components of the infection cycle to gain a better understanding of epidemic development that might lead to improved management practices. Lesions on leaves appeared 6 h after inoculation at 20°C and were larger on young 3-week-old leaves compared with 8-week-old leaves. Incidence of infection on 3-week-old leaves was lowest at 5°C, highest at 15 and 20°C, and failed to occur at 30°C. Defoliation began 48 h after inoculation at 20 and 25°C but was slower at higher and lower temperatures. Conidia production and release from colonized leaves began 48 h after inoculation at 15 and 19°C. Total conidia production was lowest at 7°C, highest at 15°C, and progressively declined at 19 and 23°C. Production of conidia lasted 2 to 3 days. Sclerotia formed mainly along the midveins and were similar in size at 5 to 15°C, largest at 20°C, and smallest at 25°C. Conidia formed directly on sclerotia that were overwintered outdoors and then incubated on moist filter paper. Conidia production began after 48 h at 10, 15, and 20°C. Total production was lowest at 5°C, highest at 20°C, failed to occur at 25°C, and ceased after 10 days at all temperatures. These data show that at optimal temperatures, relatively short wet periods are required for conidia production on overwintered sclerotia, infection of leaves, and subsequent conidia production on diseased leaves that may account for the sudden and rapid spread of disease in fields. The data will be useful for helping growers identify weather conditions favorable for disease development.

An exploration of the range of expert opinions on the optimum storage temperature for apples and pears in RA (refrigerated air), CA (controlled atmosphere), and DCA (dynamic controlled atmosphere) is provided, based on the accumulated postharvest data from the last 20 years. Apple cultivars have been divided into two storage temperature groups (0 to 1 °C and >1 °C), based on chilling sensitivity. Increasingly, gradual cooling, rather than rapid cooling, is recommended for apple cultivars, especially for chilling-sensitive cultivars. European pear cultivars are held at storage temperatures close to or just below 0 °C since they are not chilling-sensitive, and most cultivars require a cold temperature to induce ethylene production and ripening, especially if picked early for long-term storage. Asian pears apparently have higher temperature requirements in CA, compared with European pears. The temperature recommendations for RA and CA storage differ in some apple and European pear cultivars. In such cases, the CA recommendation is, on average, approximately 0.9 °C higher for apple cultivars and approximately 0.5 °C higher for pear cultivars, compared with RA. Research evidence suggests that some apple and pear cultivars can be stored at higher temperatures in DCA than in CA, and if the ethylene inhibitor, 1-methylcyclopropene (1-MCP), is applied in CA and/or DCA, leading to possible energy savings and quality benefits. A cool growing season may increase postharvest disorders, depending on cultivar and region. The store or packinghouse manager may choose to mitigate potential postharvest problems by maintaining the storage temperature at or above the temperature listed here and/or using stepwise (gradual) cooling. The storage temperature can affect the humidity and vapour pressure deficit (driving force) in the storage room. Altering the vapour pressure deficit controls the water loss in stored fruit, which can affect various quality parameters and the occurrence of several storage disorders.

Storage trials of 4 and 8 months’ duration, using ‘Bartlett’ pear ( Pyrus communis ) fruit treated with and without aminoethoxyvinylglycine (AVG) and stored using ultra low oxygen (ULO) storage (1.5 kPa O 2 ) versus dynamic controlled atmosphere (DCA) (≈ 0.6–0.7 kPa O 2 ) based on chlorophyll fluorescence were conducted over 2 years. AVG applied preharvest and DCA storage produced pears with significantly lower respiration, ethylene, acetaldehyde, ethyl acetate and ethanol post-storage compared to the other treatment combinations. Lower volatiles reflected a higher level of fruit quality. AVG + DCA also exhibited greater green color and firmness retention than the other treatment combinations. There were few disorders in both years of study, with no correlation with field and storage treatments, with the exception of pear scuffing, which was only present in year 2. The incidence of scuffing was positively associated with both fruit softening and yellowing, with DCA + AVG showing the lowest incidence (10%) and ULO + control, the highest (65%). Softening occurred during the shelf life period, as required, and was not an issue for any treatment combination. However, uneven degreening was a concern for fruit treated with DCA + AVG (mainly when firmness at harvest was > 85 N). Future research on higher maturity levels at harvest or reduced AVG rates could address this concern.

Background and goals Winter temperature inversions in 2020 and 2022 saw much of Nova Scotia drop below-20 & DEG;C, with the coldest vineyards registering below-25 & DEG;C. With sizable plantings of both interspecific hybrids and Vitis vinifera L., we examined both in terms of bud hardiness, viability, and the regional historical frequency of like events. A pruning study using one hybrid and one V. vinifera site tested whether minimal pruning should remain the recommendation in a highly damaged cane-pruned system.Methods and key findings Bud hardiness measurements using differential thermal analysis across 44 sites, 16 cultivars, and two years showed regional hybrids to be 3 & DEG;C hardier, on average, than V. vinifera. Pre-and postfreeze bud viability data reflected this difference. Historical data indicates that the frequency of winter events equal in severity or worse than recent damaging winter events has decreased from occurring annually 100 years ago, to once every five years today. Pruning trials using a range of pruning severities showed that no treatment produced a marketable crop in the more damaged Chardonnay, while retaining extra canes was as effective as minimal pruning in Vidal blanc. Minimal pruning reduced vigor, limited pruning options, and greatly increased pruning time the following year. Carryover treatment effects in year two were nuanced and nominal in both cultivars.Conclusions and significance A reduction in winter damage risk resulting from warming is being offset by an increase in plantings of less-hardy V. vinifera cultivars in the region. Results from the pruning trials challenge the notion that minimal pruning after a damaging freeze event is universally the best practice in a cane-pruned system.

The microbiome, an influential factor affecting plant health and growth, is attracting increasing interest with respect to wine grape production. The purpose of this study was to characterize the microbiome (fungi and bacteria) of the soil, cover crop roots, and grape (Vitis spp.) roots across rootstock and depth in a cool-climate, organic vineyard. The cover crop consisted of a fescue (Festuca sp.) grass, while grape roots were sampled from New York Muscat, a cool-climate hybrid, across three root types (ungrafted, 3309C and Riparia Gloire) at three root depths (0 to 15, 15 to 30, and 30 to 50 cm). The grape root microbiome was more specialized, with fewer observed amplicon sequence variants for both bacteria (16S) and fungi (internal transcribe spacer) than found in the cover crop and the surrounding soil. Grape roots were dominated by bacterial genera Pseudomonas, Niastella, and Rhizobium; most prominent fungal genera were Plectosphaerella, Trichosporon, and Ilyonectria. Although no correlations were found between α-diversity metrics and soil parameters, Pseudaleuria relative abundance was correlated with Mn, Fe, and Na levels. Soil depth explained a small portion of bacterial but not fungal variance and taxonomic composition. Rootstock type explained a portion of both bacterial and fungal variance and taxonomic composition, substantiating the role of host plant genetics in the development of the grape root microbiome. This is the first characterization of the grape root microbiome in a cool-climate Canadian vineyard.

Plant-parasitic nematode populations were analyzed from composite soil samples collected from 62 vineyard blocks throughout Nova Scotia in 2018 and 2019. Nematode groups of potential concern that were found included ring nematodes (family Criconematidae), dagger nematodes (Xiphinema spp.), and root-knot nematodes (Meloidogyne spp.). Ring nematodes were overall the most widespread and abundant group of plant-parasitic nematodes, recovered from 79% of blocks with an overall average population density of 114 nematodes per 100 cm3 soil. Ring nematodes tended to be more abundant in older blocks. DNA sequence analyses of a subset of the ring nematode populations confirmed the presence of Mesocriconema xenoplax, which is the species known to be damaging to and most widely associated with grapevine globally. The analyses indicated that Criconema permistum was also present, notably in samples with the greatest ring nematode population densities. The results indicate that ring nematodes could be affecting the health of Nova Scotia vineyards, particularly in the future as populations continue to develop in relatively young vineyards and as older blocks are replanted. Additional research is needed to delineate the distribution of M. xenoplax vis-a-vis other species and to experimentally assess the host-parasite relationship between C. permistum and grapevine.

A physiological disorder known as 'stem-end flesh browning' has recently been found in 'Gala' apples in the USA, Canada, and Brazil. The browning originates at the stem end but can extend throughout the fruit with increasing severity. The effects of harvest date, plant growth regulators (PGRs) (aminoethoxyvinylglycine (AVG) (ReTain) and 1-methylcyclopropene (1-MCP) (Harvista)), postharvest 1-MCP (SmartFresh), storage temperature (0.5 and 3 degrees C), and storage method (standard controlled atmosphere (CA) and dynamic controlled atmosphere - chlorophyll fluorescence (DCA-CF)) have been investigated. A Harvista spray was more effective at reducing disorder incidence than a ReTain or SmartFresh treatment. DCA-CF also delayed disorder development, but did not prevent it. Disorder incidence was slightly lower at 3 degrees C than 0.5 degrees C, indicating an advantage to using a slightly warmer storage temperature. The occurrence of stem-end flesh browning can be reduced by pre- and postharvest management through the use of Harvista and DCA-CF, respectively, while also using a storage temperature of 3 degrees C.

Since the early 1960s, DPA has been the primary method to control superficial scald, a major disorder in stored apples and pears. In November 2009 the European Commission formally refused the inclusion of diphenylamine (DPA) and ethoxyquin into Annex I of Directive 91/414/EEC which lists its approved pesticides. This presentation will review the research and development of low O-2-based DCA technologies as a commercial replacement for DPA. Beginning with experiments that began over 110 years ago in 1903, research showed that superficial scald in apples and pears is entirely prevented by storage in very low O-2 concentrations, i.e., between 0 and 1% O-2. However, some of this work indicated that low O-2 fails to control or sometimes increases superficial scald. In addition, there was no reliable method to measure the lowest acceptable concentration and some research suggested that if the O-2 is too low for too long, fruit damage occurs. Lastly, controlled-atmosphere (CA) room construction and control was not always sufficient to maintain adequate low O-2 conditions (e.g., < 1%). Therefore, the use of CA to control superficial scald was not embraced by industry. However, in the 1980s as CA room construction and gas control became more advanced, industry began testing low O-2 methods to replace DPA, e.g., 0.7% O-2 on 'Delicious' apple in British Columbia, Canada, initial low O-2 stress (ILOS) (various countries) and RLOS (repeated low O-2 stress with ethanol monitoring). The advent of DCA-Chlorophyll Fluorescence (DCA-CF) technology in 2001, which determines the lowest acceptable level of O-2 in storage, removed the fear of fermentation and low O-2 damage and gave the fruit industry more confidence to use DCA-CF (rather than DPA), for controlling superficial scald. Data will be shown on the transition to CA-based technologies to control superficial scald in the apple industry of South Tyrol, Italy, where DPA has not been used for 3 years. A new method is being tested called DCA-CF 'Extra' which may add extra scald prevention during shelf-life for very superficial scald-prone apples.

DeLong, J., Prange, R., Harrison, P., Nichols, D. and Wright, H. 2014. Determination of optimal harvest boundaries for Honeycrisp™ fruit using a new chlorophyll meter. Can. J. Plant Sci. 94: 361–369. In this study, a new chlorophyll measurement tool [the delta absorbance (DA) meter] was used to develop an optimal harvest maturity model for Honeycrisp™ fruit. Apples from nine commercial orchards in the Annapolis Valley, Nova Scotia, Canada, were sampled over 11 consecutive weekly harvests during the 2010, 2011 and 2012 growing seasons. At each harvest, a sample of fruit was measured for its DA (IAD) values, firmness, titratable acidity (TA),% soluble solids content (SSC), red skin coloration and internal core ethylene. Following approximately 3 mo of storage at 3.5°C, samples were removed and assessed for disorder incidence. The optimal harvest period was identified by aligning all “at harvest” IAD values, fruit quality measurements and “post-storage” disorder data with the corresponding harvest week. Then, the IAD values associated with the harvests having high commercial fruit quality and the least collective expression of disorders, delineated the optimal harvest boundaries. As IAD units declined during fruit maturity, the upper boundary value of 0.59 was deemed “when to begin” harvest, while the lower boundary value of 0.36 was deemed “when to end” harvest for long-term storage. The use of the DA model approach for optimal harvest delineation is potentially applicable to all commercial apple cultivars, but should be developed for each within a distinct growing region.

The use of chlorophyll fluorescence in fruit and vegetable storage (HarvestWatch (TM)) was first introduced at the ISHS CA symposium in 2001 in Rotterdam, The Netherlands and was first commercially adopted in the 2003-2004 storage season in Washington State, USA and South Tyrol, Italy. Although there are many potential postharvest applications for chlorophyll fluorescence that will be reviewed, research and commercial adoption has focussed primarily on its use in optimising the O-2 concentration in dynamic controlled-atmosphere (DCA) storage of fruits and vegetables. This is achieved through a novel method of detection of a sudden change in fluorescence at the lower O-2 limit (LOL). The reasons for its adoption are: real-time monitoring and control of product, pesticide-free technique, accurate determination of LOL, control of storage disorders, especially superficial scald in susceptible apple and pear cultivars without use of pesticides such as diphenylamine (DPA), improved retention of quality, possible flavour enhancement and detection of senescence, decay or incorrect storage conditions, i.e., temperature. A summary of the current use of HarvestWatch (TM) will be presented. Preliminary results from applications in other high value fruits, e. g., extension of green-life in banana, 'programmed DCA' for avocado, will be presented as evidence of possible future applications.

Programmed cell death (PCD) plays an important role in several plant developmental processes. The phytohormone ethylene has been implicated in PCD signalling in many plant systems, but it is also important in developmental processes such as seed germination, flowering, and climacteric fruit ripening. Lace plant (Aponogeton madagascariensis (Mirbel) H. Bruggen) is an aquatic monocot that develops perforated leaves via the deletion of cells through developmentally regulated PCD. The plant is ideal for studying PCD; however, little is known about the regulation of cellular death involved in this system. The current study examines ethylene as a potential signalling molecule in lace plant PCD and investigates climacteric-like behaviour during lace plant leaf development. Whole plants were treated with the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG), the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), or a combination of both. Subsequently, ethylene levels were monitored, and leaf development was analyzed. The results indicate that ethylene is involved in lace plant PCD signalling. AVG-treated plants had significantly lower ethylene outputs and a significant reduction in perforation formation. The inhibitory effect of AVG was recovered when AVG and ACC were applied simultaneously. The data presented here show for the first time, to our knowledge, climacteric-like behaviour during the remodelling of leaves.

Since its introduction in 2001, chlorophyll fluorescence-based technology has proven capable of sensing several stresses that may affect fruit and vegetable quality in storage, e. g., O-2, CO2, temperature, 1-MCP application and the presence of ammonia. Application of a stress results in an increase in the chlorophyll fluorescence parameter, F-alpha. The most popular application is the detection of the lower oxygen limit (LOL), which correlates with respiratory-based indicators of the LOL. Detecting the LOL and storing at or just above the LOL can result in a reduction in several apple and pear disorders in addition to increased quality retention. If CO2 was included in combination with O-2 just above the LOL, the F-alpha baseline value gradually increased in some cultivars, e. g., 'Golden Delicious', suggesting a CO2-induced stress. If the CO2 was low, i.e., <2.0 kPa, there were no CO2-related disorders and an improvement was noted in firmness and titratable acid retention. Exposure to chilling temperatures was associated with an increase in the F-alpha baseline. And the addition of a low-intensity background light to prevent 'dark adaptation' enhanced the F-alpha increases associated with chilling stress. In 1-MCP-treated fruit, there was a transient increase in the F-alpha signal. The 1-MCP transient stress effect in the first 50 h was associated with transient CO2 and ethylene production increases. An accidental leak of ammonia refrigerant into a commercial store room of apples resulted in a stress-like increase in F-alpha. A group of carotenoid pigments (violaxanthin, antheraxanthin and zeaxanthin) can be enzymatically inter-converted through the xanthophyll cycle. Experimental results indicate the xanthophyll cycle operates as part of the plant cell's response to low O-2 stress, i.e., violaxanthin decreased, and zeaxanthin and the xanthophyll de-epoxidation state (DEPS) increased. These results suggest: 1) chlorophyll fluorescence is capable of detecting not only low-O-2 stress but also other stresses; 2) storage using chlorophyll fluorescence technology allows for constant monitoring and control of O-2, to achieve maximum quality benefits, including disorder control, without the use of postharvest chemicals; and 3) the xanthophyll cycle is involved in stress effects on chlorophyll fluorescence.

The lower oxygen limit (LOL) in plants may be identified through the measure of respiratory gases [i.e. the anaerobic compensation point (ACP) or the respiratory quotient breakpoint (RQB)], but recent work shows it may also be identified by a sudden rise in dark minimum fluorescence (F o). The interrelationship between aerobic respiration and fermentative metabolism, which occur in the mitochondria and cytosol, respectively, and fluorescence, which emanates from the chloroplasts, is not well documented in the literature. Using spinach (Spinacia oleracea), this study showed that Fo and photochemical quenching (q P) remained relatively unchanged until O2 levels dropped below the LOL. An over-reduction of the plastoquinone (PQ) pool is believed to increase F o under dark + anoxic conditions. It is proposed that excess cytosolic reductant due to inhibition of the mitochondria’s cytochrome oxidase under low-O2, may be the primary reductant source. The maximum fluorescence (F m) is largely unaffected by low-O2 in the dark, but was severely quenched, mirroring changes to the xanthophyll de-epoxidation state (DEPS), under even low-intensity light (≈4 μmol m−2 s−1). In low light, the low-O2-induced increase in F o was also quenched, likely by non-photochemical and photochemical means. The degree of quenching in the light was negatively correlated with the level of ethanol fermentation in the dark. A discussion detailing the possible roles of cyclic electron flow, the xanthophyll cycle, chlororespiration and a pathway we termed ‘chlorofermentation’ were used to interpret fluorescence phenomena of both spinach and apple (Malus domestica) over a range of atmospheric conditions under both dark and low-light.

Storing of some pear cultivars has usually included a reliance on postharvest chemical treatments, e. g., ethoxyquin or diphenylamine, to control superficial scald. The current trend towards elimination of pre-and post-harvest synthetic chemical treatments in Europe and other markets necessitates a change to reliance on other, preferably non-chemical, methods to achieve scald and quality control. Previous research has demonstrated this can be accomplished with storage at very low O-2 levels. Wide-spread adoption, however, has not taken place due to concerns of anaerobic damage when the pear fruit are held below the lower oxygen limit (LOL) for long periods of time. Dynamic controlled-atmosphere (DCA) storage is able to identify the LOL of pears using chlorophyll fluorescence. It is termed 'Dynamic' CA since it allows the storage manager to customise the O-2 concentration at the beginning of storage and change it during storage, as the LOL changes. DCA is appealing because it: 1) is non-chemical, 2) uses existing CA technology, 3) can be monitored electronically in real-time, 4) extends the storage time of fruit, 5) controls superficial scald and other storage disorders, and 6) can warn the operator of equipment malfunctions, e. g., refrigeration and CA equipment failure. The principal of DCA is based on the discovery that a sudden increase in the fruit's fluorescence occurs at the LOL. If the O-2 concentration is increased, by as little as 0.2% above the LOL, the fruit can be safely stored. This has allowed apples and pears to be stored below 1.0% O-2 and as low as 0.4% O-2, thereby achieving both longer storage life and superficial scald control in scald-prone fruit.DCA has been used commercially since 2004. In 2010, ca. 300,000 to 400,000 bins of fruit were stored using this technology, mainly in the North American and European apple industries. Its use is increasing at more than 40% per year. It is useful for extending the marketing window of pears and as an alternative to ethoxyquin for controlling superficial scald in pear fruit.

A link between the minimum fluorescence (F-o) and a metabolic shift from predominantly aerobic to fermentative metabolism [i.e, the lower oxygen limit (LOL] is the foundation of dynamic controlled atmosphere (DCA). Current DCA technology uses pulse frequency modulated (PFM) sensors and employs a range of light intensities and extrapolation to measure F-alpha, an approximation of F-o. Like fruit mass, colour, sugar or acid levels, the LOL is inherently variable, even between apples (Malus domestica) (for example) from a given cultivar and tree or between the sun-exposed and shaded regions of a single fruit. The physiological link between metabolism and fluorescence has not been extensively studied. However, recent work suggests the low-O-2-induced rise in F-alpha results from a shut down of mitochondrial function and a buildup of reductant that leads to an over-reduction of the plastoquinone (PQ) pool and a decrease in photochemical quenching. Hypoxic conditions above the LOL can decrease F-alpha slightly in some species, possibly as a result of zeaxanthin formation and increased non-photochemical quenching. Low-intensity light differentially affects F-alpha depending on the O-2 level: light increases F-alpha when O-2 levels are above the LOL due to light-induced reduction of the oxidized PQ pool, but decreases the elevated F-alpha signal below the LOL as a result of a PSI-driven oxidation of the over-reduced PQ pool. Temperature has a negative, primarily non-physiological correlation with the F-alpha baseline which seems unrelated to the PQ pool redox state. Understanding how O-2 and other factors affect F-alpha may improve the utility and commercial application of DCA. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.