Experimental In-Field Transfer and Survival of Escherichia coli from Animal Feces to Romaine Lettuce in Salinas Valley, California.

This randomized controlled trial characterized the transfer of E. coli from animal feces and/or furrow water onto adjacent heads of lettuce during foliar irrigation, and the subsequent survival of bacteria on the adaxial surface of lettuce leaves. Two experiments were conducted in Salinas Valley, California: (1) to quantify the transfer of indicator E. coli from chicken and rabbit fecal deposits placed in furrows to surrounding lettuce heads on raised beds, and (2) to quantify the survival of inoculated E. coli on Romaine lettuce over 10 days. E. coli was recovered from 97% (174/180) of lettuce heads to a maximal distance of 162.56 cm (5.33 ft) from feces. Distance from sprinklers to feces, cumulative foliar irrigation, and lettuce being located downwind of the fecal deposit were positively associated, while distance from fecal deposit to lettuce was negatively associated with E. coli transference. E. coli exhibited decimal reduction times of 2.2 and 2.5 days when applied on the adaxial surface of leaves within a chicken or rabbit fecal slurry, respectively. Foliar irrigation can transfer E. coli from feces located in a furrow onto adjacent heads of lettuce, likely due to the kinetic energy of irrigation droplets impacting the fecal surface and/or impacting furrow water contaminated with feces, with the magnitude of E. coli enumerated per head of lettuce influenced by the distance between lettuce and the fecal deposit, cumulative application of foliar irrigation, wind aspect of lettuce relative to feces, and time since final irrigation. Extending the time period between foliar irrigation and harvest, along with a 152.4 cm (5 ft) no-harvest buffer zone when animal fecal material is present, may substantially reduce the level of bacterial contamination on harvested lettuce

Rates and Methods of Application of Nitrogen and Phosphorus for Commercial Field Production of Head Lettuce in Southcentral Alaska

Head lettuce (Lactuca sativa L.) is one of the major agricultural crops grown in Alaska. In 1992, its wholesale value was approximately $314,000, second only to potatoes among Alaska’s commercially field grown vegetables (Brown et al., 1992). The quality of head lettuce is as important as yield, as lettuce heads that do not meet minimum size and weight standards are unmarketable. Head size and weight are strongly influenced by management practices, dictating a high level of management for successful commercial production. Among manageable cultural variables, rate of fertilizer application and the method of fertilizer placement are two of the most critical. Despite the value of the head lettuce crop to Alaska vegetable growers and the importance of fertilization as a management practice, little research has been published on rates of application and method of applying nitrogen and phosphorus to commercially grown head lettuce

Microbiological quality of lettuce (Lactuca sativa) consumed on the streets of Maroua (Cameroon: Effect of disinfecting agents used by some vendors

This study was carried out to determine and compare the microbiological quality of lettuce (Lactuca sativa) from market (unwashed) and those ready to eat in Maroua. The results revealed that 92.3% of lettuce vendors in Maroua, used Chlorine and 7.7% used potassium permanganate as cleaning method. The microbial concentration of lettuce varied from one vendor to another. Total flora ranged from 2.3 to 4.9 Log CFU/g for unwashed samples and from 2 to 4.51 Log CFU/g for washed samples; fungi counts were comprised between 0.76 to 2.65 Log CFU/g for unwashed samples and 0.26 to 2.17 Log CFU/g for washed samples; total coliforms ranged from 2.84 to 3.60 Log CFU/g for unwashed, and 0.26 to 3.00 Log CFU/g for washed lettuce; fecal coliforms ranged from 1.29 to 3.60 Log CFU/g for unwashed samples and 1.70 to 3Log CFU/g for washed samples. These results show also that Vibrio spp. was found amongst the 69% of unwashed samples, but was absent in all the washed samples. Salmonella spp. was present in 85% samples of unwashed lettuce, but absent in washed samples. The results revealed also that; there was a significant difference between the bacterial concentration of unwashed and washed lettuce samples (P<0.05). Most of the analysed samples (92%) composed of washed and unwashed samples were not satisfactory for consumption. (Résumé d'auteur

CONSUMER ATTITUDES TOWARD ORGANICALLY GROWN LETTUCE

This research shows that approximately 29 percent of lettuce purchases in California expect to purchase an organically grown lettuce product in the future. Organic lettuce purchasers are more likely to be female, have a higher household income and a higher level of education. Consumers are concerned with the freshness, quality, price, and environmental impact of the lettuce they purchase.Consumer/Household Economics,

Nutritional and sensory evaluation of ready-to-eat salads during shelf life

The evolution of the antioxidant and sensory properties of six commercially available ready-to-eat salads, rocket, iceberg lettuce, baby lettuce, lamb’s lettuce, curly endive and radicchio, was studied throughout the shelf life. Both the storage under modified atmosphere and in unsealed pouch in a domestic refrigerator were considered and compared. Ascorbic acid, total phenolics content and antioxidant capacity were chosen as the most representative nutritional parameters for this purpose. The data obtained were analyzed by Principal Component Analysis (PCA). Radicchio, lamb’s lettuce and rocket showed an initial higher content of the quality parameters studied and demonstrated a better resistance to air exposure than the other salads, being ascorbic acid the most affected parameter. Modified atmosphere packaging demonstrated to be a very useful and reliable technology to extend nutritional and sensory properties during the shelf life period for all the vegetables studied

Faecal contamination of lettuce heads after manure application

In recent years, an increasing number of disease outbreaks have been associated with consumption of contaminated vegetables. Thus, it has been speculated to what extent such contamination is associated with application of animal manure as fertilizer, which is particularly practiced in organic vegetable production where conventional fertilizers are prohibited. A field survey was therefore performed aiming to assess the survival and transfer of E. coli from animal manure to lettuces, with E. coli serving as an indicator of bacterial enteric pathogens. Animal manure was applied to 3 Danish fields prior to planting of lettuce seedlings, then 5-8 weeks later at the normal time of harvest, inner and outer leafs of 10 lettuce heads were pooled into one sample unit with a total of 50 pools per field. Additionally, in one field, 15 soil samples were collected weekly until the harvest time. E. coli was enumerated by plating 1 mL of 10-fold serial dilutions of 5 g of homogenized sample material, i.e. manure, soil and lettuce onto PetrifilmTM Select E. coli count plates (3M), which were then incubated 24 h at 44°C. The manure applied to the fields contained 3.0-4.5 Log10 E. coli CFU/g and E. coli was found in 36-54% of the pooled lettuce samples with a detection limit of 10 CFU/g. Numbers of E. coli in 14-20% of pooled lettuce samples exceeded a satisfactory microbiological hygiene criteria level of 100 CFU/g. The highest percentage of faecally contaminated lettuce heads (54%) coincided with the shortest growth period studied indicating that the time gap between application of manure and harvest and the survival of E. coli (and pathogens) influences the contamination of lettuce via manure amended soil. However, at the time of harvest, the numbers of E. coli in 5 of 15 soil samples were reduced below the detection limit and no samples exceeded 100 CFU/g. This is in contrast to the lettuce samples, where 20% of faecally contaminated samples had >100 E. coli/g, which may indicate that faeces contamination of crops could originate from alternative sources, such as contaminated water and wildlife. Comparisons of the genotype of isolated E. coli strains could help to elucidate this

Chitin mixed in potting soil alters lettuce growth, the survival of zoonotic bacteria on the leaves and associated rhizosphere microbiology

Chitin is a promising soil amendment for improving soil quality, plant growth, and plant resilience. The objectives of this study were twofold. First, to study the effect of chitin mixed in potting soil on lettuce growth and on the survival of two zoonotic bacterial pathogens, Escherichia colt O157:H7 and Salmonella enterica on the lettuce leaves. Second, to assess the related changes in the microbial lettuce rhizosphere, using phospholipid fatty acid (PLFA) analysis and amplicon sequencing of a bacterial 16S rRNA gene fragment and the fungal ITS2. As a result of chitin addition, lettuce fresh yield weight was significantly increased. S. enterica survival in the lettuce phyllosphere was significantly reduced. The E. coli O157:H7 survival was also lowered, but not significantly. Moreover, significant changes were observed in the bacterial and fungal community of the lettuce rhizosphere. PLFA analysis showed a significant increase in fungal and bacterial biomass. Amplicon sequencing showed no increase in fungal and bacterial biodiversity, but relative abundances of the bacterial phyla Acidobacteria, Verrucomicrobia, Actinobacteria, Bacteroidetes, and Proteobacteria and the fungal phyla Ascomycota, Basidiomycota, and Zygomycota were significantly changed. More specifically, a more than 10-fold increase was observed for operational taxonomic units belonging to the bacterial genera Cellvibrio, Pedobacter, Dyadobacter, and Streptomyces and to the fungal genera Lecanicillium and Mortierella. These genera include several species previously reported to be involved in biocontrol, plant growth promotion, the nitrogen cycle and chitin degradation. These results enhance the understanding of the response of the rhizosphere microbiome to chitin amendment. Moreover, this is the first study to investigate the use of soil amendments to control the survival of S. enterica on plant leaves

Modelling the growth of Salmonella spp. and Escherichia coli O157 on lettuce

This study aimed to model the growth of Salmonella and Escherichia coli O157 on lettuce at different temperatures. Microorganisms were inoculated separately on lettuce and stored at 5, 10, 25, and 37°C. Growth curves were built by fitting the data to the Baranyi’s DMFit model and Ratkowsky equation was used as secondary model. The models were able to assess the growth of both microorganisms and data showed that bacteria did not growth for 24 hours at 10°C, what can be a suitable temperature for lettuce distribution on food services. However, prolonged periods demonstrated growth at every temperatures examined

Returns to investment in IPM research in lettuce by NSW DPI

Research into IPM technologies has been conducted by NSW DPI for over 20 years. Evaluating the returns from investment in specific research and development projects is an important component of the NSW DPI science and research program. An economic evaluation has been conducted of IPM in managing invertebrate pests in lettuce in NSW. We found that there has been widespread adoption of IPM practices amongst NSW lettuce growers leading to a flow of economic benefits to the lettuce industry and the community. Important environmental and human health benefits were also identified. A benefit-cost ratio of 2 was calculated for the return to NSW DPI investment in lettuce IPM research which while satisfactory, is lower than returns calculated for other agricultural R&D evaluations. It does not include ‘spillover’ benefits to other States nor have human health or environmental benefits been valued.research, benefit-cost, evaluation, IPM (Integrated Pest Management), lettuce, Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,

The inheritance of resistance to bacterial leaf spot of lettuce caused by Xanthomonas campestris pv. vitians in three lettuce cultivars.

Lettuce yields can be reduced by the disease bacterial leaf spot (BLS) caused by the pathogen Xanthomonas campestris pv. vitians (Xcv) and host resistance is the most feasible method to reduce disease losses. The cultivars La Brillante, Pavane and Little Gem express an incompatible host-pathogen interaction as a hypersensitive response (HR) to California strains of Xcv resulting in resistance. Little was known about the inheritance of resistance; however, resistance to other lettuce pathogens is often determined by resistance gene candidates (RGCs) encoding nucleotide-binding leucine-rich repeat (NB-LRR) proteins. Therefore, we determined the inheritance of BLS resistance in the cultivars La Brillante, Little Gem and Pavane and mapped it relative to RGCs. The reaction to Xcv was analyzed in nine F1, F2 and recombinant inbred line populations of lettuce from HR×compatible or HR×HR crosses. The HR in La Brillante, Pavane and Little Gem is conditioned by single dominant genes, which are either allelic or closely linked genes. The resistance gene in La Brillante was designated Xanthomonas resistance 1 (Xar1) and mapped to lettuce linkage group 2. Xar1 is present in a genomic region that contains numerous NB-LRR encoding RGCs and functional pathogen resistance loci in the RGC2 family. The Xar1 gene confers a high level of BLS resistance in the greenhouse and field that can be introgressed into commercial lettuce cultivars to reduce BLS losses using molecular markers