Lettuce Industry Research Articles

Lettuce Plant Trace-Element-Deficiency Symptom Identification via Machine Vision Methods

Lettuce is one of the most widely planted leafy vegetables in plant factories. The lack of trace elements in nutrient solutions has caused huge losses to the lettuce industry. Non-obvious symptoms of trace element deficiency, the inconsistent size of the characteristic areas, and the difficulty of extraction in different growth stages are three key problems affecting lettuce deficiency symptom identification. In this study, a batch of cream lettuce (lactuca sativa) was planted in the plant factory, and its nutrient elements were artificially controlled. We collected images of the lettuce at different growth stages, including all nutrient elements and three nutrient-deficient groups (potassium deficiency, calcium deficiency, and magnesium deficiency), and performed feature extraction analysis on images of different defects. We used traditional algorithms (k-nearest neighbor, support vector machine, random forest) and lightweight deep-learning models (ShuffleNet, SqueezeNet, andMobileNetV2) for classification, and we compared different feature extraction methods (texture features, color features, scale-invariant feature transform features). The experiment shows that, under the optimal feature extraction method (color), the random-forest recognition results are the best, with an accuracy rate of 97.6%, a precision rate of 97.9%, a recall rate of 97.4%, and an F1 score of 97.6%. The accuracies of all three deep-learning models exceed 99.5%, among which ShuffleNet is the best, with the accuracy, precision, recall, and F1 score above 99.8%. It also uses fewer floating-point operations per second and less time. The proposed method can quickly identify the trace elements lacking in lettuce, and it can provide technical support for the visual recognition of the disease patrol robot in the plant factory.

Economic impacts of food safety incidents in a modern supply chain: E. coli in the romaine lettuce industry

AbstractFood‐safety incidents disrupt impacted markets, cause destruction of edible product, shake consumer confidence, and impose economic losses upon participants across the implicated supply chain. Despite the prevalence of such incidents, we know surprisingly little about their supply chain impacts, especially in modern produce markets where contracts may impede the diffusion of price impacts through the supply chain. The November 2018 E. coli incident for romaine lettuce in Central California roiled North American produce markets throughout the fall of 2018 and well into 2019. Our study of the economic impacts of this incident benefited from access to disaggregate information on prices and sales for romaine and substitute leafy greens at all stages of the supply chain, enabling us to overcome data limitations that have impeded prior studies. We decompose impacts from the incident into price and quantity components. Romaine growers were largely protected from damage due to fixed‐price provisions in grower‐processor contracts. Economic losses were incurred mostly by romaine shippers and processors, and grocery retailers who pulled saleable product from the supply chain and lost sales during and well after the incident due to reduced consumer demand. We estimate that the total societal loss from the incident was in the range of $276–$343 million. Widespread and long‐lasting impacts from a food‐safety incident demonstrate the economic benefit of industries adopting mandatory food‐safety standards and improved traceability to minimize the occurrence and impacts of such incidents.

Investigation on the Microbial Diversity of Fresh-Cut Lettuce during Processing and Storage Using High Throughput Sequencing and Their Relationship with Quality.

Microbial community distribution in vegetables can affect their quality. This study analyzed the distribution of the microbial community at various stages during processing and storage with the microbial diversity analysis, and evaluated the correlation between the dominant bacteria and sensory quality of lettuce using correspondence analysis with multiple regression analysis. Results showed that the process of washing, cutting, then disinfection and dewatering could change the community distribution and dominant bacteria in lettuce, and maintain better texture, morphology, aroma, color qualities of lettuce. The total number of colonies and relative abundance of Xanthomonas in fresh-cut lettuce decreased, while Afipia and Ralstonia increased during processing and pre-storage (storage for 6 h, 12 h and 1 d). After storage for 3 d, the total number of colonies in lettuce increased (more than 5 log CFU/g), especially the relative abundance of Pseudomonas, which led to the obvious deterioration of the sensory quality of lettuce. Throughout the process, the number of Bacillus cereus, Staphylococcus aureus, and E. coli was less than 100 CFU/g and 3 MPN/g. The number of typical pathogenic bacteria, Salmonella, Listeria monocytogenes and E. coli O157:H7, was below the detection limit. Overall, the prevention and control of psychrotrophic Pseudomonas in lettuce was still necessary. These results will provide useful information for the fresh-cut lettuce industry.

In-Field Evaluation of Drone-Released Lacewings for Aphid Control in California Organic Lettuce.

Aphids are one of the most economically important pests to California's Central Coast lettuce industry. Aphids vector the lettuce mosaic virus and are crop contaminants in the packaging of the product. Lettuce aphid, Nasonovia ribisnigri (Mosley) (Hemiptera: Aphididae), is one of the predominant aphid species in lettuce, and it poses unique management challenges forming colonies inside the lettuce head. Current management practices rely on repeated foliar insecticide applications to reduce aphid densities per plant. Some organic growers have explored the release of laboratory-reared beneficial insects to manage aphids in their commercial fields. This project sought to document the effects of drone-released lacewing eggs on lettuce aphid densities in organic romaine lettuce fields. Commercially reared lacewing eggs were released at a rate of 74,131 eggs/ha and organic-certified insecticides were sprayed following their respective label recommendations. Our results could be interpreted as preliminary evidence that drone release of lacewings could reduce aphid densities (15.6-150.0 aphids/lettuce head) when compared to the untreated plots (32.1-257.9 aphids/lettuce head). Aphid densities were also decreased after the application of foliar organic-certified insecticides (11.77-143.5). Traditionally, the cost of labor has limited the use of beneficials in the lettuce production system, but the use of drones for these releases may make this strategy more attractive. Based on our calculations, spraying an organic-certified insecticide is less expensive (direct operational costs of U.S. $ 116.36/ha) than releasing beneficial insects by hand ($ 185.40) or by drone ($ 176.00) when mimicking the conditions of this study.

Comparative transcriptomics and metabolomics analyses provide insights into thermal resistance in lettuce (Lactuca sativa L.)

High temperature poses a major threat to sustainable development of the lettuce industry. Investigation of the mechanisms that regulate heat stress responses has great significance. Four lettuce accessions-two thermotolerant and two thermosensitive cultivars-were selected for comparative analysis. Subsequently, the metabolic changes in lettuce in response to heat treatment were investigated using untargeted metabolomic analysis. Several discriminatory metabolites were identified, including three amino acids, one carbohydrate, eight phenolic compounds, one terpene, one alcohol and one lignin. Transcriptomics analysis was performed in parallel using the same four lettuce accessions. The integrated analysis suggested that a large number of metabolites and genes detected with measurable changes during the heat response are involved in flavonoid biosynthesis. Additionally, 25 of the 31 transcription factors identified, including MYBs, WRKYs, NACs, bHLHs, MADSs, AP2/ERFs and bZIP, were also upregulated. Thus, this study provides a comprehensive understanding of the complex molecular mechanisms underlying the thermal stress responses of lettuce.

Bacterial Leaf Spot of Lettuce Disease: An Unpredictable Enemy to the Florida Lettuce Industry

Bacterial leaf spot (BLS) of lettuce is caused by the bacterium Xanthomonas hortorum. BLS is more damaging in Florida, where the climate is conducive for disease development. The most effective control method is host resistance currently being developed by the UF/IFAS lettuce breeding program in all lettuce types. This new 4-page publication of the UF/IFAS Horticultural Sciences Department was written by Germán Sandoya and D. Calvin Odero.

Harvest of Lettuce from Verticillium-Infested Fields Has Little Impact on Postharvest Quality.

Verticillium wilt of lettuce, caused by the soilborne pathogen Verticillium dahliae, poses a serious threat to the California lettuce industry. Knowledge of disease development and its impact on postharvest marketability would facilitate better management of the affected fields. This study investigated postharvest marketability of 22 lettuce varieties harvested from two Verticillium-infested commercial lettuce fields in Salinas and Watsonville, CA, in 2005 using a randomized complete block design. Periodic sampling to monitor disease in several crisphead varieties in the field demonstrated that root symptoms developed quickly at later stages of heading, followed by the onset of foliar symptoms as the crop reached harvest maturity. Harvested marketable heads were vacuum cooled soon after harvest to about 4°C and maintained at this temperature in commercial coolers. The impact of V. dahliae on postharvest marketability was assessed based on the percentage of heads per case deemed marketable following 1, 2, and 3 weeks of refrigerated storage. Across both field experiments, the average disease incidence and postharvest marketability ranged from 4.2 to 87.5% and from 69.4 to 100.0%, respectively, among lettuce types and varieties. The Pearson correlation analysis detected no significant relationship between disease incidence and postharvest marketability across all varieties tested (r = 0.041, P = 0.727), or within lettuce types, even though V. dahliae was recovered from 34% of the plants harvested, and recovery ranged from 0 to 73.3% for V. dahliae and from 10 to 91.7% for non-V. dahliae (V. isaacii or V. klebahnii) species. These findings demonstrate that growers can harvest lettuce from an infested field before foliar symptoms develop with negligible impact by Verticillium spp. on postharvest marketability or quality.

Multilocus Sequence Typing of Strains of Bacterial Spot of Lettuce Collected in the United States.

Studies on genetic diversity and recombination in bacterial pathogens are providing a better understanding of the mechanisms shaping bacterial diversity, which can affect disease control. Xanthomonas campestris pv. vitians, causal agent of bacterial leaf spot of lettuce, is a threat to the worldwide lettuce industry. We examined the genetic variation within a sample of 83 strains from California, Florida, and Ohio using multilocus sequence typing of six housekeeping genes, totaling 2.7 kb. Additionally, polymorphism in two virulence-related genes, hrpB2 and a putative glycosyl hydrolase, were examined. Based on housekeeping genes, we found three genetic groups of strains that were all able to induce the disease. These included strains collected from weeds and irrigation water that had haplotypes identical to strains from diseased lettuce. High linkage disequilibrium across the sequenced loci indicates that the pathogen is predominantly clonal but recombination has contributed to the observed sequence variation. Although there was significant genetic variation in X. campestris pv. vitians within and among sampled states, identical haplotypes were observed across all three states. This finding suggests that seedborne inoculum may contribute to the diversity of X. campestris pv. vitians in the United States. Knowledge of the genetic structure of the pathogen may be used for developing resistant lettuce varieties.

Genetic Variation for Shelf-life of Salad-cut Lettuce in Modified-atmosphere Environments

Packaged salad-cut lettuce (Lactuca sativa L.) for food service and salad mixes is an increasingly important component of the lettuce industry. The product is highly perishable; cold storage and modified-atmosphere (MA) packaging are used to extend its shelf life. Given the importance of this market, lettuce cultivars, breeding lines, and populations should be selected for increased shelf life in MA environments. The objectives of this research were to determine the genetic variation in lettuce for shelf life in low-O2 MA environments and to develop rapid evaluation methods suitable for a lettuce breeding program. Lettuce was processed from field-grown plants of 33 romaine and three crisphead cultivars over 2 years. Shelf life was evaluated after storage in MA bags and in CO2-free controlled-atmosphere (CA) chambers with gas ratios of 0.2% O2:99.8% N2, 1.0% O2:99.0% N2, or 5.0% O2:95.0% N2. Deteriorated leaf blade tissue was water soaked and wilted with a dull to dark or black color, and midrib tissue and heart leaves were water soaked with a translucent to dark brown color. Genetic variation for shelf life was detected using MA bags or CA chambers, and the results from both years and testing methods were significantly correlated. Oxygen concentration did not affect shelf life in the CA chamber experiment, which indicated that the observed symptoms in the majority of cultivars were probably not from low O2 damage or CO2 injury, although multiple mechanisms of deterioration may be involved. Selection for lettuce cultivars, breeding lines, and populations with extended shelf life is possible using MA bags or CA chamber testing methods and could facilitate a consistent release of germplasm with stable shelf life in MA environments.

Indirect non-target effects of insecticides on Tasmanian brown lacewing ( Micromus tasmaniae) from feeding on lettuce aphid ( Nasonovia ribisnigri)

Tasmanian brown lacewing, Micromus tasmaniae (Walker) (Neuroptera: Hemerobiidae), is an indigenous aphid predator in New Zealand and Australia. Lacewing mortality can result directly from contact with insecticides and/or indirectly from the consumption of insecticide-intoxicated prey. Laboratory bioassays were set up to examine the indirect non-target effects of insecticides on M. tasmaniae populations feeding on lettuce aphid, Nasonovia ribisnigri (Mosley). Larvae of M. tasmaniae were initially tested against three commonly used insecticides at two dose rates (approximate recommended field rate and half field rate). 1st to 4th instar aphids were fed on insecticide-treated lettuce for 24 h and then fed to 1st instar M. tasmaniae larvae. Pirimicarb (Pirimor ® 50) caused 30–40% mortality of M. tasmaniae larvae exposed at 1st instar for 3 days. Pymetrozine (Chess ® WG) showed less than 20% mortality, while imidacloprid (Confidor ®) caused over 96% mortality of M. tasmaniae larvae over this period. A dose–response bioassay was then set-up to determine the impacts of lower doses of imidacloprid through until pupal development of M. tasmaniae larvae. There was no increase in mortality due to low doses (one sixth field rate or less) but from days three to eight, M. tasmaniae larvae showed significant evidence of delayed developmental rate from 3rd instar larvae into pupae. These results demonstrate that the use of imidacloprid, pirimicarb and pymetrozine for control of lettuce aphid has indirect non-target effects on M. tasmaniae. These effects need to be considered in developing Integrated Pest Management (IPM) systems for the New Zealand lettuce industry.

GENETIC ANALYSIS OF RESISTANCE TO LETTUCE DROP CAUSED BY SCLEROTINIA MINOR

GENETIC ANALYSIS OF RESISTANCE TO LETTUCE DROP CAUSED BY SCLEROTINIA MINOR

Use of 1‐methylcyclopropene to extend the postharvest life of lettuce

AbstractThis study examined the effect of fumigation of iceberg lettuce with 1‐methylcyclopropene (1‐MCP) at 0.1–1 µl l−1 for 1–5 h on the storage life at 5 °C in air containing 0.1 µl l−1 ethylene. 1‐MCP extended the storage life of shredded lettuce at all concentrations, with the optimal treatment being fumigation with 0.1 µl l−1 1‐MCP for 1 h at 5 °C, which resulted in an extension in storage life of about 50% over untreated lettuce. Application of this treatment to whole lettuce heads resulted in a 100% increase in storage life. 1‐MCP thus appears to be of considerable commercial potential for the lettuce industry.© 2002 Society of Chemical Industry

Manufacturing Green Gold: Capital, Labor and Technology in the Lettuce Industry.

Manufacturing Green Gold: Capital, Labor and Technology in the Lettuce Industry.

Manufacturing Green Gold: Capital, Labor and Technology in the Lettuce Industry. By William H. Friedland, Amy E. Barton, and Robert J. Thomas. ASA Rose Monograph Series. Cambridge University Press, 1981. 159 pp. Cloth, $24.95; paper, $8.95

Manufacturing Green Gold: Capital, Labor and Technology in the Lettuce Industry. By William H. Friedland, Amy E. Barton, and Robert J. Thomas. ASA Rose Monograph Series. Cambridge University Press, 1981. 159 pp. Cloth, $24.95; paper, $8.95

Reviews

Book reviewed in this article: Aggregate Supply Response of Crops in a Developing Region. By S. L. Bapna. Sultan Chand & Sons, Land Use and Living Space. By Robin H. Best. Methuen, Population and Technology. By ESTER Boserup. Innovation Diffusion: A New Perspective. By Lawrence A. Brown. Methuen, Science and Agricultural Development. Edited by Lawrence Busch. Data Collection in Developing Countries. By D. J. Casley and D. A. Lury. The Economic Theory of Agricultural Land Tenure. By J. M. Currie. Marketing Behaviour: Issues in Managerial and Buyer Decision‐Making. By Gordon Foxall. Manufacturing Green Gold: Capital, Labor and Technology in the Lettuce Industry. By W. H. Friedland, A. E. Barton and R. J. Thomas. Rural Employment: Trends, Options, Choices. By Ian Hodge and Martin Whitby. Maidens, Meal and Money: Capitalism and the Domestic Economy. By Claude Meillassoux. Maidens, Meal and Money: Capitalism and the Domestic Economy. By Claude Meillassoux. Implications of Tractorisation for Farm Employment, Productivity and Income (volumes I and II). Performance of Futures Markets: The Case of Potatoes. By A. B. Paul, K. H. Kahl and W. G. Tomek. Poverty and Famines: An Essay on Entitlement and Deprivation. By Amartya Sen. Biological Efficiency in Agriculture. By C. R. W. Spedding, J. M. Walsingham and A. M. Hoxey.

‘Salinas’ Lettuce1

Abstract In the last 2 decades, 2 cultivars of lettuce (Lactuca sativa L.) have dominated the western U.S. lettuce industry. The first, ‘Calmar’ was released by the University of California in 1960. For several years in the mid-1960's, it was planted on nearly all the spring, summer and early fall acreage in the Salinas Valley and other coastal districts in California. It is a large, vigorous cultivar of the Great Lakes type. The second, ‘Vanguard’, was released by the USDA in 1958 and for many years has been the mainstay cultivar for early spring production in the Imperial Valley and other desert districts. Each cultivar has spawned a group of selections, a ‘Calmar’ group and a ‘Vanguard’ group, which have increased the adaptive range of the original cultivars.

Conditions and Consequences of Lettuce Harvest Mechanization1

Abstract This article projects the conditions under which the iceberg lettuce industry would make the transition to a mechanized harvest system and the social consequences of such a transition. Impediments to labor supply and increased production costs could spur a transition to mechanization. In addition to impacts on the character of the labor force and the impacts upon the communities surrounding lettuce production areas, labor force displacement could be as high as 87%.

Contributions of applied science to the lettuce industry of the southwest

Integrated achievements of plant breeders, soil scientists, agricultural engineers and refrigeration specialists, along with increased market demands, have raised the American lettuce industry from a $6 million business in 1918 to one of $108 million in 1949.

A Case Study in Risk Distribution: The California Lettuce Industry

A Case Study in Risk Distribution: The California Lettuce Industry