A study was made of the characteristics of harvested lettuce heads in Arizona during the 1964-65 season. Information on size, weight, firmness and number of wrapper leaves of each head sampled was collected and set up for analysis. No results were available at the time of this progress report.

No description available.

A series of studies on lettuce fertilization have been carried out over the past few years. Fertilizer applications increased yield through increased head size and did not affect the number or quality of harvested heads. The lower rates used were as effective as the higher rates. Nitrogen and phosphorus fertilization generally increased the nitrate and phosphorus content of the various plant parts selected for analysis.

No description available.

Lettuce stand problems in desert production areas are, in many instances, related to high seedbed temperatures and the use of seed coatings. We evaluated the use of fusicoccin and other growth regulators to improve the performance of naked and coated lettuce seeds at high temperature. Treatment of both naked and coated seeds with fusicoccin markedly increased the rate and total emergence of seedlings incubated at 35 °C for 10 hours alternating with 23 °C for 14 hours.

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Gypsum was applied preplant on spring lettuce at rates of zero, 2 tons per acre, and 4 tons per acre. There were no significant differences in carton yields or in carton weights. Postharvest soil analyses showed that the application of four tons of gypsum per acre significantly increased the calcium and magnesium levels in the saturated paste solution. There were no significant effects of gypsum application on ESP and SAR values, nor in pH or sodium concentrations.

In 1988, Arizona's early- season lettuce crop was plagued by disease and insect problems, both intensified by unseasonably high temperatures. In the western Arizona production area, an epidemic of lettuce infectious yellows (LIY) resulted in serious economic losses to growers. The yellows disease is incited by the LIY virus (LIYV), a plant virus transmitted by the sweet potato whitefly [Bemisia tabaci (Gene.)]. Disease symptoms in lettuce include stunted growth, rolling yellowing and /or reddening of infected leaves; necrotic lesions appear at or near the leaf margins at latter stages of the disease. LIYV has a wide host range which increases the difficulty of isolating lettuce fields from LIYV infected or whitefly-infested fields; also, whiteflies are resistant to insecticides. Therefore, host-plant resistance appears to be the most promising means of reducing losses due to this disease. To initiate a breeding program, commercial lettuce cultivars and breeding lines (Lactuca sativa L.), and related, cross-breeding wild lettuce species (L. serriola L. and L. saligna L.) were screened for resistance to LIYV in the western Arizona production area using natural inoculation by residence whiteflies.

Lettuce infectious yellows virus (LIYV), a recently recognized plant virus, causes dramatic yellowing symptoms and severe diseases in a wide range of vegetable crops in Arizona, adjacent southwestern states and Mexico. Until now, the only available diagnostic method was a time-consuming bioassay that used the insect vector to transmit the virus, with subsequent manipulation of indicator plants. A rapid, sensitive diagnostic technique (termed an indirect enzyme-linked immunoassay, called indirect ELISA) system was developed to detect lettuce infectious yellows virus (LIYV) in infected plant material. A virus specific antibody was made to viral capsid protein which was purified by polyacrylamide gel electrophoresis. The indirect ELISA system was optimized and used to detect viral antigen in greenhouse-inoculated melons. The system was subsequently adapted to detect LIYV in symptomatic and asymptomatic weed and cultivated plant species collected from infected fields near Yuma and in central Arizona. The indirect ELISA system described here allows for the detection of approximately 100 ng of virus per well. The LIYV was detectable in symptomatic (but not in asymptomatic) leaves of melon plants infected with the virus. In contrast, the virus could be detected in both symptomatic and symptomless cheeseweed plants collected in the field. The optical density readings for infected weed species were generally lower than those for cultivated species, such as melons, lettuce, and spinach, suggesting that there is less virus in the weed hosts tested than in infected, cultivated hosts.

No description available.