In the United States, illnesses associated with fresh produce are increasing in frequency.  While contamination risks are present at every aspect of the farm to fork continuum, post-harvest practices holds the potential for cross-contamination of large amounts of product.  Post-harvest contamination risks for hydroponically grown lettuce packaged with intact roots and sold as "living lettuce"" are poorly understood.  In this study, transmission of Salmonella enterica serotype Enteritidis to the roots and leaves of butterhead lettuce was studied when contamination was introduced during typical handling practices.  The effectiveness of random sampling strategies for selection of Salmonella contaminated leaves was assessed by co-inoculating the Salmonella solution with Glo Germ™ and comparing recovery from blacklight selected leaves.  The recovery of Salmonella was improved by only 0.5 log CFU/g when blacklight was used to select Glo Germ™ contaminated leaves (P=0.05). This suggests random leaf selection as described by current FDA protocols is adequate. In addition, this study showed rapid transfer of Salmonella from liquid to the roots and sub-sequentially to the leaves of living lettuce.  Salmonella persisted but did not grow on leaves when stored at 4˚C for 18-days. Storage at 12˚C was associated with 2 log CFU/g increases in Salmonella on roots after 18-days storage (P=0.0002), while 4˚C storage was associated with a decrease of 0.4 log CFU/g Salmonella on roots (P=0.0001). Growth occurred only under temperature abuse conditions.  This reinforces the need for maintaining temperature control and highlights the importance of identifying risks associated with post-harvest handling during hydroponic production and distribution. / Master of Science in Life Sciences

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No description available.

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Pankar-huyus are becoming an alternative solution to the Bolivian Altiplano's climate problems for agriculture and to help provide adequate nutrition for the inhabitants of this region. Pankar-huyus are small modules with mild ambient temperatures that cover roughly 4 m^2. They are built underground and are covered by agrofilm caps that, in this study, were partially opened by day and closed at night. This study evaluated the climactic parameters of minimum and maximum temperature, minimum and maximum relatively humidity inside the pankar-huyus, wind velocity outside and inside the pankar-huyus at 40 cm from the soil and at the level of the soil (thus obtaining net ratiation). The crop planted was Grand Rapids TBR--variety lettuce. The study tested two depths, 0.80 m and 1.20 m, of the pankar-huyus combined with two different degrees of cover opening, of 20 cm and 40 cm. The lettuce was planted twice (two cultivation cycles). The first was in September to October, the second from November to December. These two cycles in the present study are the two time periods mentioned. The first cycle's nursery was a walipini with disinfected soil, and the plants developed without problems. The second cycle's nursery was planted in another walipini with a non-disinfected surface, which resulted in a fungal infection that directly affected the second cycle's yield. The climate parameters were measured by instruments, which were: Thermohydrometers to measure temperature and humidity, anemometer to measure wind velocity, and a luxó to measure solar radiation. Of the combination of variables in this study, modules with a depth of 1.20 meters and a 40 cm opening gave the highest yield for this crop, despite the second crop being notably affected by a fungal infection. One of the advantages of this type of system is the favorable minimum temperatures for temperate crops. Among its disadvantages are the elevated maximum temperatures and the high minimum relative humidity of some of the modules, especially those with 0.80 m depths. Solar radiation was observed to diminish as it penetrated deeper depths inside the modules. Wind velocity did not have much influence on the magnitude inside the modules. However, greater velocity was measured on the soil, which is the center of the modules. The exterior climate factors that directly affected the interior of the modules were: maximum temperature, minimum relative humidity, and wind velocity because these occurred when the modules' covers remained open. Solar radiation is one of the principal parameters because it gives the energy necessary for all the crop's biochemical and metabolic processes.

Three separate experiments were conducted to determine the influence of depth of transplanting on the size and shape of head of crisp-head lettuce. A hotbed experiment was conducted in the winter of 1950-1951. A greenhouse experiment was conducted in the spring and early summer of 1951. A final experiment, which was a modification of the other two, was conducted in the field in the early summer of 1951. The variety of lettuce used was Imperial 44 for all three experiments. The lettuce was seeded in a seed flat and transplanted to Bird-10 Vita-Bands 1 ½ inches by 1 ½ inches in size. The plants were then transplanted into the growing areas at shallow, medium, and deep transplanting depths. The hotbed and greenhouse experiments were inconclusive in their results but were of value in giving practice and growth information which made the field experiment more satisfactory in results. The results of the field experiment showed that deep transplanted lettuce produced heads more conical, more compact, and more curly leaved than lettuce transplanted medium or shallow. The core length of deep transplanted lettuce was shorter than the core of shallow or medium transplanted. The heads from all three transplanting depths were the same in height but were significantly different in width. Heads from the deep transplanted plants had the narrowest width and were definitely more concial than the shallow or medium transplanted. The heads from the three transplanting depths weighed the same, which indicated the deep transplanted heads were smaller because they were more firm. The shape of head was influenced by the added mechanical pressure of the soil around the plants. The compactness of head and conical shape of the deep transplanted plants appeared to be the result of soil pressure around the plant. Very compact heads, as observed on the deep treated plants, are undesirable where the lettuce is to be used as a garnish or in a sandwich because it is difficult to remove a leaf intact from such a head. The results of this experiment indicates that deep transplanting of crisp-head lettuce should be avoided, and that the more shallow the plants are transplanted the more desirable the size and shape of the heads will be. / Master of Science

The objectives of this research were i) to observe the movement of the wetting front in subsurface drip irrigated lettuce and broccoli, 2) to analyze variability in soil water tension (SWT) within the profile, and 3) to determine root distributions of subsurface drip irrigated lettuce and broccoli. Lettuce and broccoli plots at the Maricopa Agricultural Center during the 1992-93 and 1993-94 winter growing seasons were intensively instrumented with automated tensiometers. During both seasons, there was good agreement between mean daily SWT, and SWT measured before irrigation. During 1992-93, the maximum variation in mean SWT among tensiometers was 2.5 kPa. Among tensiometers within the zone of greatest root density, the maximum variation was only 1.5 kPa. Therefore, the range of SWT within the lettuce root zone was small, and tensiometer placement anywhere within the root zone would have been adequate. During 1993-94, the maximum variation in mean SWT among tensiometers was 7 kPa. The maximum variation among tensiometers within the zone of greatest root density was 5.3 kPa. The larger variation in mean SWT among tensiometers, compared to lettuce, is due to the greater water use of broccoli. Tensiometer placement will be more critical for higher water use crops. During both seasons roots proliferated around the drip tubing. These results substantiate the assumption that tensiometer placement anywhere within the zone of greatest root density will be adequate for irrigation scheduling of subsurface drip irrigated crops.

The objective of this research was to estimate a season -long water balance under one subsurface trickle- irrigated plot each of lettuce (Lactuca sativa L. var. Waldmann's Green) and broccoli (Brassica olearacea L. var. Claudia). One lettuce plot during 1992-93 and one broccoli plot during 1993-94 were intensively instrumented with automated tensiometers. Tensiometer readings and estimates of evapotranspiration were used to estimate seasonal water contents in the crop root zone, and water losses due to leaching. For the monitored portion of the 1992-3 growing season, 19.1 an of irrigation water was applied, 12.5 cm of rainfall fell, and ET, was 11.5 cm. Estimated deep percolation was 60% of total water applied (irrigation plus rainfall). Leaching was periodic, and was mostly associated with rainfall events. During the monitored portion of the 19934 season, 21.2 cm of irrigation water were applied, 8.0 an of rainfall fell, and ET, was 21.9 cm. Estimated deep percolation was 28% of total water applied. Almost all of this leaching was associated with one major rainfall event. Water stored in the root zone (top 50 cm) was relatively constant at 12-14 cm water/50 cm soil except after rainfall.

Admire (imidacloprid), applied as a soil treatment, protected lettuce plants from developing infestations of green peach aphid, Myzus persicae (Sulzer), for 60-100 d after planting based on two small plot and two commercial field trials. Admire applied 7.6 cm sub-seed furrow provided longer and more consistent protection from green peach aphid than treatments applied to the soil surface, as a side-dress, or 15.2 cm sub-seed furrow. Surface band applications of Admire provided inconsistent control probably because of inadequate hydrological incorporation into the soil. In small plot trials, effective control of aphids by Admire applied 7.6 cm sub seed furrow resulted in greater than 90.0% marketable heads while the untreated plots contained 20.0% marketable heads. When used in a commercial setting, Admire applied 7.6 cm sub-seed furrow on leaf lettuce prevented aphid colonization (<3 aphids per plant) for approximately 100 d after planting, while the untreated and commercial standard treated areas contained 30.7 and 26.8 aphids per plant respectively at 100 d after planting. In addition, marketability of lettuce was greater in Admire treated plots. As a sub-seed furrow treatment, Admire provides a more suitable approach to aphid control than is currently available with foliar insecticides.