Lettuce (Lactuca sativa) is a highly perishable horticultural crop. It has a relatively short shelf life due to leaf senescence that limits its commercial value. Postharvest senescence varies with influences of environmental and genotypic factors. This study aims to elucidate the molecular mechanisms contributing to postharvest senescence in lettuce. Weare investigating the transcriptional changes of twelve senescence-associated genes (SAGs) in four lettuce cultivars, accession 60184, ‘Manatee’, ‘Tall Guzmaine’, and ‘Okeechobee’ during postharvest storage. Among those lettuce varieties, accession 60184 has the shortest shelf life while ‘Okeechobee’ has the longest shelf life. The other two cultivars have intermediate shelf life. To explore the function of SAGs in lettuce, CRISPR-Cas9 knockout mutants were generated for functional characterization. We further compared the genotypic and morphological characteristics of the cultivars. Additionally, global gene expression patterns were conducted across the four lettuce cultivars using RNA-sequencing to uncover genetic variations. The results of this study will provide genetic resources for breeding new lettuce cultivars with improved postharvest longevity and higher commercial value.

Lettuce (Lactuca sativa L.) is grown worldwide, from temperate to subtropical climates. Spring season production in humid, subtropical regions, such as southern Florida, is characterized by rising ambient temperatures that can stress lettuce to prematurely bolt and lose shelf life. The objectives of this research were 1) to identify genetic variability in heat tolerance and shelf life among lettuce types and accessions grown under humid, subtropical conditions, and 2) to understand the genotype × environment (G × E) interaction to estimate shelf life of these lettuce accessions. Five lettuce types (romaine, crisphead, butterhead, leaf, and Latin) were grown under commercial conditions in the Everglades Agricultural Area near Belle Glade, FL, USA, for five field experiments over two seasons. Lettuce heads were evaluated at harvest, and subsets were transported to a local commercial grower/shipper for vacuum-cooling and storage at 15 °C according to previously determined protocols for accelerated shelf life testing. Visual appearance ratings were made across harvests and storage time points to segregate lettuce accessions with an estimated marketable shelf life >14 days. The breeding lines tested in this research had head weight and marketability comparable to commercial cultivars. Notably, the crisphead accessions 50113, 60157, 60159, and H1098 had the highest estimated and actual shelf life of more than 21 days, with no presence of bolting or tipburn. Meanwhile, romaine, butterhead, leaf, and Latin types had accessions with estimated and actual shelf life ranging from 14 to 28 days and no presence of bolting or tipburn. A G × E analysis indicated that this interaction is significant; therefore, breeders should consider analyzing G × E when developing new cultivars with good horticultural characteristics, longer shelf life, and most importantly, adaptation to warmer humid, subtropical conditions.

Lettuce is a highly perishable horticultural crop with a relatively short shelf-life that limits its commercial value and contributes to food waste. Postharvest senescence varies with influences of both environmental and genetic factors. From a larger pool of romaine lettuce genotypes, we identified three genotypes with variable shelf lives and evaluated their leaf morphology characteristics and transcriptomic profiles at preharvest to predict postharvest quality. Breeding line 60184 had the shortest shelf-life (SSL), cultivar ‘Manatee’ had an intermediate shelf-life (ISL), and ‘Okeechobee’ had the longest shelf-life (LSL). We observed significantly larger leaf lamina thickness and higher stomatal index in the SSL genotypes relative to the LSL cultivar. To identify molecular indicators of shelf-life, we used a transcriptional approach between two of the contrasting genotypes, breeding line 60184 and cultivar ‘Okeechobee’ at preharvest. We identified 552 upregulated and 315 downregulated differentially expressed genes between the genotypes, from which 27% of them had an Arabidopsis thaliana ortholog previously characterized as senescence associated genes (SAGs). Notably, we identified several SAGs including several related to jasmonate ZIM-domain jasmonic acid signaling, chlorophyll a–b binding, and cell wall modification including pectate lyases and expansins. This study presented an innovative approach for identifying preharvest molecular factors linked to postharvest traits for prolonged shelf.

Pink rib discoloration or pinking in the midribs of lettuce (Lactuca sativa) leaves is a stress-induced disorder that leads to crop loss worldwide. Maintaining recommended field and postharvest conditions reduces its incidence but does not eliminate the issue. During the past decade, research has identified the tolerance of this disorder among lettuce types and cultivars grown in cooler climates. However, tolerance to pink rib among lettuce types grown in humid subtropical climates is unknown; therefore, it is necessary to screen lettuce germplasm under these growing conditions. During this study, diverse lettuce accessions were planted for early-season, mid-season, and late-season harvests over two seasons in Belle Glade, FL, USA. Harvested midribs were wounded to induce pink rib, stored for 6 to 9 days at 5 °C and >95% relative humidity, and rated for severity using a 5-point subjective scale. Genotype × environment interactions were evaluated to understand the environmental factors that favor the development of pink rib during storage and between planting seasons. Pink rib severity increased during storage, with the highest increase observed after 3 to 4 days in both seasons. After 9 days of storage, lettuce accessions with the least pink rib for each leaf type were identified. The lowest pink rib ratings after 9 days of storage were “moderate” (rating of 3) for crisphead, Latin, and romaine, “slight” (rating of 2) for butterhead types, and “none” (rating of 1) for leaf types. Additionally, pink rib severity increased among accessions during the late spring season harvest when field temperatures were higher and daylight hours were extended. The lettuce germplasm with low susceptibility to pink rib is promising to breed lettuce lines for future research.

Pink rib discoloration is a physiological disorder resulting in loss of quality and marketability of minimally processed and whole head lettuce (Lactuca sativa L.). Although the biochemistry of pink rib is complex and a comprehensive understanding is lacking, multiple research efforts have focused on inhibiting or reducing pink rib through exogenous application of small molecules such as L-cysteine. In this study, the effects of naturally occurring phytochemicals [serotonin (0.5 or 1 g L-1), naringenin (0.5 g L-1), L-cysteine (0.5 g L-1), and melatonin (1 g L-1)] on pink rib expression were examined in iceberg and Romaine lettuce. The exogenous application of these natural compounds was investigated for reduced pink rib discoloration in lettuce during simulated commercial storage and examined for metabolite and enzymatic activity changes. Immersing wounded midribs for 30 s in serotonin, naringenin, or L-cysteine solutions had no or only a slight inhibitory effect to inhibit pink rib discoloration while those immersed in a melatonin solution had reduced development of pink rib in both iceberg and Romaine lettuces after 5 d at 5 degrees C. Phenylalanine ammonia lyase (PAL) activity and chlorogenic acid concentration increased upon pink rib discoloration, consistent with previous reports. However, melatonin-treated samples did not result in reduced PAL activity, chlorogenic acid content, or polyphenol oxidase (PPO) activity. Untargeted metabolite analysis showed that melatonin treatment resulted in a global effect on metab-olite changes in the wounded lettuce midrib tissue. To compare the severity of pink rib among treatments, pink rib was quantified throughout storage visually and by converting digital images of the lettuce midribs to the L*a*b* color space. The a* component of L*a*b* represents redness versus greenness, thus its values were used to objectively measure pink rib severity. Melatonin was shown to be a promising compound to minimize devel-opment of pink rib discoloration at cut surfaces of iceberg and Romaine lettuce during commercial handling and storage.

Volatile organic compounds or VOCs in mature fresh peaches constitute the aroma and flavor perceived by consumers. This study compared four fresh late-season commercial peach cultivars ('Augustprince', 'Early Augustprince', 'Early Big Red', and 'Flameprince') grown in Fort Valley, GA, USA in 2015 and 2016 for the presence and abundance of individual volatile compounds. Fruit were harvested at commercial maturity and stored in a refrigerated room for 5-7 days at 5 +/- 2 degrees C, followed by 2-3 days at room temperature (21 +/- 1 degrees C) for ripening. Ripen fruit (<1 kg f for puncture and <1 kg f g(-1) for compression and Kramer firmness tests) were used. Volatiles were extracted by headspace solid-phase micro-extraction (HS-SPME) and separated on a gas chromatograph-mass spectrometer (GC-MS). Compounds were then identified using the NIST MS library based on their mass spectra. Concentrations of individual compounds were calculated using the peak area and concentration of the internal standard (1,3-dichloro benzene). The primary compounds associated with these peaches included: alcohols, esters, hydrocarbons/alkanes, aldehydes, and lactones. Thirty-four compounds were identified in 'Early August Prince' (EAP) in both seasons. These compounds were previously reported to be in fruit and/or plants. Thirty-three and 30 compounds were found in 'Augustprince' (AP) fruit during 2015 and 2016, respectively. Thirty-two compounds were observed in 'Early Big Red' (EBR) in 2015 and 20 in 2016. Twenty-five compounds were identified for 'Flameprince' (FP) in both seasons. In 2015, hexenol, hexyl ethanoate, benzaldehyde, and.-decalactone were the prominent hexane, ester, aldehyde, and lactone compounds, respectively. In 2015, alcohols showed no trend for compounds being predominantly higher in concentration. Similar results were found in 2016, with the exception of (E)-2-hexen-1-ol as the prominent hexane. Esters were the most abundant compounds in 2016 while lactones were the most abundant compounds in 2015. EBR cultivar in both seasons had the highest concentration for lactone compounds (272 ng g(-1) in 2015 and 238.9 ng g(-1) in 2016) and esters in 2016 (810.8 ng g(-1)). Esters and lactones give peaches their fruity and floral aromas. Understanding the chemical make-up of individual cultivars and their seasonal variation can provide insight into the different cultivars and their capabilities in regard to fresh peach aroma and flavor.

Peach production in Georgia, USA, extends from mid-May to mid-August. Multiple cultivars are commercially grown in the U.S., and each cultivar has unique fruit quality characteristics, which could influence consumer perception and acceptability. Among those, peach flavor has been minimally characterized among cultivars. Headspace-solid phase microextraction (HS–SPME) combined with gas chromatography–mass spectrometry (GC–MS) was used to characterize the volatile profile of 42 peach cultivars commercially grown in 2016. The goal of this research was to understand the aroma composition and content of peach cultivars grown in Georgia, USA. Thirty-six volatile compounds were identified. Significant differences (p ≤ 0.0001) were observed for all the flavor volatiles across all cultivars being evaluated. Esters were the major compounds isolated from the 42 peach cultivars, followed by lactones, alcohols, aldehydes, and terpenoids, in that order. Lactones, benzaldehyde, and linalool, which are known to be peach aroma compounds, exhibited the highest mean concentrations among the cultivars with ɣ- and δ-decalactones having a concentration of approximately 180 ng·g−1 and 60 ng·g−1, respectively. Among the cultivars, “Majestic” had the highest mean concentration of ɣ-decalactone, followed by “Southern Pearl” with approximately 503 ng·g−1 and 443 ng·g−1, respectively. “Southern Pearl” and “Fairtime” also exhibited the highest average concentration of δ-decalactone. The results obtained will help provide an understanding of the distribution of the various volatile organic compounds found in Georgia-grown peach cultivars.

The postharvest life of lettuce ( Lactuca sativa ) is variable and negatively affected by mechanical injury, incomplete cooling, and poor genetic quality. Lettuce breeders are developing cultivars with a longer shelf life and rely on subjective, destructive, and time-consuming methods for quality analysis. One method of accelerating quality evaluations is known as accelerated shelf-life testing (ASLT), which has the potential to assist breeders in assessing lettuce quality and shelf life. The objective of this research was to determine the quality traits that significantly affect shelf life to develop an ASLT procedure to rapidly assess the postharvest quality of lettuce accessions in breeding programs. In Test 1, Romaine lettuce quality was evaluated using one subjective and five objective parameters during storage at 5, 10, 15, or 20 °C. Results determined that weight loss, lightness*, and hue* angle were best correlated with the overall appearance rating, whereas storage at 10 or 15 °C differentiated the shelf-life potential quickly and without excessive deterioration. In Test 2, these objective characteristics and storage temperatures were used to study rates of quality deterioration of a commercial Romaine cultivar (Okeechobee) and a breeding line (60182), both with long shelf lives, and a Batavia lettuce cultivar (La Brillante) with a short shelf life. Lettuce was evaluated during storage at 10 °C (winter and spring seasons) or at 15 °C (winter season). Weight loss was the most appropriate quality index for lettuce at these storage temperatures for a single harvest, whereas lightness* and hue* angle were the most appropriate indices for comparing quality between harvests. To apply ASLT to postharvest assessments of lettuce, breeders and other researchers should include two controls with good and poor shelf life (similar to ‘Okeechobee’ and ‘La Brillante’, respectively) as standard baseline cultivars during storage at either 10 or 15 °C.

Like fungi and some prokaryotes, plants use a thiazole synthase (THI4) to make the thiazole precursor of thiamin. Fungal THI4s are suicide enzymes that destroy an essential active-site Cys residue to obtain the sulfur atom needed for thiazole formation. In contrast, certain prokaryotic THI4s have no active-site Cys, use sulfide as sulfur donor, and are truly catalytic. The presence of a conserved active-site Cys in plant THI4s and other indirect evidence implies that they are suicidal. To confirm this, we complemented the Arabidopsis tz-1 mutant, which lacks THI4 activity, with a His-tagged Arabidopsis THI4 construct. LC-MS analysis of tryptic peptides of the THI4 extracted from leaves showed that the active-site Cys was predominantly in desulfurated form, consistent with THI4 having a suicide mechanism in planta. Unexpectedly, transcriptome data mining and deep proteome profiling showed that barley, wheat, and oat have both a widely expressed canonical THI4 with an active-site Cys, and a THI4-like paralog (non-Cys THI4) that has no active-site Cys and is the major type of THI4 in developing grains. Transcriptomic evidence also indicated that barley, wheat, and oat grains synthesize thiamin de novo, implying that their non-Cys THI4s synthesize thiazole. Structure modeling supported this inference, as did demonstration that non-Cys THI4s have significant capacity to complement thiazole auxotrophy in Escherichia coli. There is thus a prima facie case that non-Cys cereal THI4s, like their prokaryotic counterparts, are catalytic thiazole synthases. Bioenergetic calculations show that, relative to suicide THI4s, such enzymes could save substantial energy during the grain-filling period.

The objective of these studies was to compare cooling methods and subsequent effects on shelf life and quality maintenance of Indian bitter melon, smooth bitter melon (Momordica charantia L.) and long bean [Vigna unguiculata (L.) Walp. ssp. sesquipedalis (L.) Verdc.]. All three commodities were packed in returnable plastic containers or wax cartons then either pallet hydrocooled to 5 degrees C or placed directly into the grower's storage room (4 degrees C) for room cooling and stored 14 days for quality observations. Pulp temperature for the smaller Indian bitter melon decreased 19 degrees C during 23 minutes of hydrocooling, whereas smooth bitter melons lost 10 degrees C in 21 minutes. Long beans cooled 17 degrees C within five minutes. After 14 days, bitter melon held in unwrapped cartons lost 2 to 3% more moisture than those either overwrapped immediately or partially overwrapped. Hydrocooled Indian bitter melon maintained better overall visual quality and less decay after 14 days of storage.

Peach ( Prunus persica ) production in the southeastern United States extends from mid-May to mid-September. There are ≈60 peach cultivars commercially grown. Each cultivar has unique fruit quality characteristics, which could influence consumer perception and likability. The present study is a survey of chemical and physical characteristics of mature, commercially grown, fresh peaches in Georgia. A collection of 30 cultivars was evaluated in 2015 and 2016 for soluble solids concentration (SSC), total titratable acidity (TTA), SSC/TTA ratio, texture (compression, puncture, and Kramer shear), and skin and flesh color (CIE L *, chroma, and hue color space values). There was significant variation between seasons for all variables ( P < 0.05) except for TTA ( P = 0.12), and flesh hue values ( P = 0.38). Statistical differences among cultivars within each year were reported for all variables ( P < 0.0001). SSC showed variation seasonally and among cultivars, whereas TTA variation was mainly attributed to cultivar differences. Similarly, cultivar-to-cultivar differences were found when comparing the different texture tests evaluated with cultivars such as Goldprince, Early August Prince, Flameprince, Majestic, and Red Globe having the most variation between seasons. Other cultivars analyzed had little variation between seasons. Moreover, firmness differences observed across the three texture tests were inconsistent. In peach skin color, significant variation was observed for L *, chroma, and hue among cultivars. Skin hue and chroma were highly correlated within each season ( r = 0.77 for 2015, r = 0.72 for 2016). The results of this survey demonstrate the variation of quality characteristics for a large selection of peach cultivars grown in Georgia. The information reported in this paper will be used as a baseline for further examining and understanding peach fruit quality.

Shrunken-2 (sh2) type sweetcorn is known for its slow sugar-to-starch conversion and long shelf life. It became the industry standard for fresh market sweetcorn in the mid-1990s. The industry currently ships sweetcorn with the shank attached, which complicates packing due to non-uniform ear length. In this study, sweetcorn (sh2 type) with either untrimmed shanks or trimmed shanks (2-cm in length) were immersion hydrocooled immediately or following three hours at 30 degrees C (86 degrees F), then stored at 5 degrees C (41 degrees F) and 95% relative humidity for 0, 5, or 10 days. Husk drying, silk appearance, and kernel appearance declined in overall quality uniformly, irrespective of treatment. Due to trimming, after 10 days of storage husk color was slightly dull, and light to medium green while untrimmed ears were a slightly brighter green. Sweetcorn kernels developed splitting, denting, and microbial growth, but these were unrelated to trimming or cooling treatment. Denting incidence was highest (14-15 kernels per ear) after 10 days. After 5 and 10 days, kernels from trimmed ears had slightly higher moisture content than untrimmed ears, with no variation between immediate and delayed cooling. As the storage period increased, total alcohol soluble carbohydrates [total soluble sugars (TSS)] increased; TSS in kernels from untrimmed ears rose from 5 to 17.5% (% sucrose) and those from trimmed ears from 3.5 to 12.75%. Microbial growth and denting were the limiting factors with regard to marketability, appearing in low incidence throughout kernels in all treatments after 10 days of storage. Overall ear and kernel quality was not compromised by trimming the shanks, or with delayed cooling for three hours. Trimming shanks shows promise to make sweetcorn packing more efficient.

A universal lexicon to describe the appearance, aroma/flavors, and textures/feeling factors of peaches was developed. The objective was to provide a standardized lexicon for descriptive validation. A trained descriptive panel established 29 attributes using 51 peach cultivars grown throughout the production season. This lexicon includes 18 aroma and flavor attributes to describe mature peaches as well as under-ripe and over-ripe, redness of flesh for appearance, three feeling factors, and seven terms for describing textures. Principal component analysis was used to discern if differences were found among peach samples using the lexicon terms utilized by trained panelists. Texture was the primary differentiating factor in the first dimension of the biplot followed by peach-identity in the second dimension. Additionally, the attributes peach-identity, fruity, sweet, tart, citrus, sour, along with textures and feeling factors were prominent in all peach varieties. This lexicon can be useful to identify and quantify sensory attributes in fresh peaches for food and agriculture research.Practical applicationsThe assessment of peach fruit varieties grown throughout the southeastern United States would create a basis for understanding the prominent and unique characteristics of peach varieties and their inherited variability. The peach lexicon created in this study will provide a platform for researchers and producers to understand the desirable sensory traits in peaches. It will allow comparisons among varieties currently available, create a database to be used in breeding applications, and help the growers to produce peaches with desirable sensory traits that could be commercially successful.