Lettuce is a highly nutritional crop that is sensitive to multiple stresses, including salt stress. The decreasing availability of salt-free water is posing a major challenge to growing nutritious lettuce in hydroponic systems. Despite evidence that salt stress affects yield and nutrition, its impacts on economically important growth stages are overlooked. This study addressed the knowledge gaps regarding the salt stress impact on romaine lettuce. Four independent experiments were conducted in controlled environment conditions using 2-38 lettuce genotypes, to assess the effects of salt stress at rosette or head formation. An increase in sodium chloride (NaCl) levels (0 to 150 mM) linearly decreased lettuce biomass. A positive association was observed between NaCl and sodium to potassium ion ratio. Lettuce was found to be sensitive to salt above 40 mM NaCl. The phenotyping of 38 lettuce genotypes revealed significant variability in salt stress tolerance. Genotype, Green forest exhibited a higher decline in fresh and dry biomass compared to Burgundy delight, indicating its higher sensitivity to salt stress. Sodium accumulation was significantly higher in both genotypes under salt stress, while potassium decreased in Green forest but remained relatively stable in Burgundy Delight. Hydro-primed lettuce had higher photosynthetic efficiency and oxidative stress tolerance than the control. Hydro-priming seed treatment could be used as a cost-effective priming technique to boost economic efficiency under stress. In addition, the low sodium: potassium ratio and high biomass can be used as indicators for selecting salt-tolerant genotypes.

This study occurred at the Ventilla Ecologic farm, situated in the central Altiplano of the Murillo province, 26 km from La Paz. Its objectives were to evaluate two types of irrigation, by drip and by microasperation, in spinach and Swiss lettuce in Walipinis, and to conduct an economic analysis. The genetic material used was spinach (viroflay variety) and Swiss lettuce (large-leaved variety). Chapin irrigation belts and nebulizers were used, and two tensiometers were used to determine the soil moisture. Manual planting occurred on September 1, 2002, in all experimental areas. Seeds were dispersed in a continual flow with Swiss lettuce at a density of 3.5g/m2 and three bobbins, and in spinach the density was 0.26 g/m2 in parallel, 20 cm rows with the irrigation belts on either side. The spinach harvest was spread out, while the Swiss lettuce harvest occurred all at once. A factorial arrangement was used in this study, with two factors: two levels of irrigation (drip and microasperation) and different crops (spinach and Swiss lettuce). The response variables regarding drip irrigation efficiency had a uniformity coefficient of 97%, and microasperation had 85%. The depth reached by the watered bulb after two hours of control was more than 20 cm, while the microasperation only reached 15 cm after two hours. Irrigation occurred at midday but in accordance with the readings that the tensiometers gave. The response variables studied in the crop were: percentage germination, number of leaves, plant size, leaf size, and yield. Yield showed significant differences between types of irrigation of crops. Drip irrigation was better than microasperation. The response variables that had the greatest effect on yield were number of leaves, plant size, and leaf size. The economic production analysis found negative net benefits for the first trial. In the second trial, drip irrigation netted Bs.3.54/m2 for spinach and Bs. 3.68/m2 for Swiss lettuce, recovering the investment from the first trial. In contrast, the yield from microasperation irrigation, even though the second trial had positive net results, did not recover the investment from the first trial. Finally, based on these data, drip irrigation is recommended because of its better yields and a lower installation cost.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Fresh produce is increasingly associated with foodborne outbreaks. In order to develop effective intervention and measures to reduce microbial risks, it is essential to attain a better understand the mechanisms of attachment of foodborne pathogens to fruits and vegetables. Using lettuce as a model, the attachment of Escherichia coli O157:H7 to produce surfaces was studied. Strains expressing various extracellular proteins (curli, O157-antigen, and intimin) known to influence attachment of E. coli to intestinal cells were evaluated for their physicochemical properties and ability to adhere to cut edge and whole leaf lettuce. Escherichia coli O157:H7 strains included: 0018, 43894 and 43895 (curli producing and non-producing); 86-24 (WT), F-12 (O157-antigen negative), pRFBE (O-antigen replaced on plasmid); and 86-24, 86-24Ã eae10 (intimin negative). The eleven strains were surveyed for their hydrophobicity and cell charge using hydrophobic interaction chromatography (HIC) and electrostatic interaction chromatography (ESIC) techniques. Iceberg lettuce squares (2 x 2 cm) were inoculated with E. coli O157:H7 strains separately (7.0 log CFU/square) and dried in a laminar flow hood. Lettuce was sampled before (unrinsed) and after being rinsed twice with sterile de-ionized water (rinsed). Strips (2 mm wide) of each cut edge of the lettuce were aseptically removed. Cut-edge and whole-leaf samples were homogenized and spiral plated onto Luria-Bertani agar, supplemented with nalidixic acid (50ppm), to assess levels of bacteria remaining on the lettuce leaf after rinsing. The rinse steps were not effective in significantly removing bacteria from lettuce (p>0.05). Curli-producing and non-producing strains preferentially attached to cut edge versus the whole leaf portions of lettuce (p<0.05); however the 86-24 strains showed no preference for attachment. With the exception of 0018 curli-producing and non-producing strains, presence/absence of extracellular proteins surveyed did not influence attachment of E. coli O157:H7 to either cut edge or whole leaf lettuce. There was significantly greater attachment of the curli-producing 0018 strain over the curli non-producing 0018 strain to cut and whole lettuce surfaces (p<0.05). Production of curli and O-polysaccharide significantly increased (p<0.05) the cell's overall hydrophobicity of the cell; however this did not affect attachment (p<0.05). The overall cell charge of all strains was negative; however, charge did not affect attachment of E. coli O157:H7 to lettuce. The presence of extracellular appendages (curli, O157-antigen, intimin) as well as hydrophobicity and cell charge properties had no affect on attachment of the cell to lettuce. / Ph. D.

This paper deals with certain phases of phototropic properties of two exceptional plants, the pertinent behavior of each being decidedly individualistic and in remarkable contrast to that of herbaceous plants in general. The prickly lettuce, Lactuca ludoviciana (Nutt.) DC. and the rosinweed, Silphium laciniatum L., two common Denton County, Texas, plants, have been selected for this study.