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Carlos G. Vaz, Domingos de Oliveira, and Orlando S. Ohashi

Cowpea, Vigna unguiculata (L.) Walp., is a very important legume in the diet of the population of the Amazon. Although it is autogamous, this species has a cross-pollination rate of ≈10%. Over several years, the mean productivity of cowpea has declined. We suggest that this is linked to a decrease in or an absence of pollinating insects in the fields. The objective of this study is to ascertain the pollinator contribution to cowpea production, as well as to determine the pollination type of the `BR3-Tracuateua' cultivar. In an experimental design, four treatments were compared: no pollination, with flowers in cages to prevent insect visits; open-pollination, with flowers exposed to all visiting insects; self-pollination, with flowers pollinated with their own pollen; and cross-pollination, with emasculated flowers being pollinated manually with pollen from another plant. We observed higher fruit set in the presence of pollinators (83%) than in their absence (77%, caged flowers). However, cross-pollination reduced both the number of seeds per pod and fruit set relative to self-pollination. This result suggests that pollinators have a complementary role in the yield of cowpea, by creating a mixed pollination system where self-pollination dominates.

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Abhava M. Dandekar, Gale H McGranahan, Sandra L. Uratsu, Charles Leslie, J. Steven Tebbets, and Patrick V. Vail

Insecticidal crystal protein fragments (ICPFs) of Bacillus thuringiensis (Bt) encoded by cryIA(c) gene were shown in diet incorporation studies to be lethal to codling moth (CM; Cydia pomonella) the key insect pest for walnut. However transformed walnut tissues expressing cryIA(c) with Bt codon usage patterns and native DNA sequence revealed very low levels of expression in planta. To correct this problem synthetic versions of one of these genes, cryIA(c) was used to transform walnut tissue. A total of 61 individual transgenic embryo lines were obtained. 34% of these lines (21/61) were high expressors (“class A”) demonstrating 80 to 100% mortality of first in star CM larvae and displaying no further larval development. Twelve clones (20%) were designated “class B” and these showed a marked retardation of larval development and a mortality between 40 to 79%. Embryos from the remaining 28 lines designated “class C” (46%). although transformed, were indistinguishable from the control (untransformed embryos) and showed a mortality of 0 to 39%.

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David R. Corbin, Frederick J. Perlak, David A. Fischhoff, John T. Greenplate, Zhen Shen, and John P. Purcell

Genetically modified potato and cotton crops that express insecticidal proteins from Bacillus thuringiensis (Bt) have recently been commercialized. These crops display autonomous resistance to specific insect pests, and thus offer major agricultural and environmental benefits. We have implemented a microbial screening program to discover new types of insecticidal proteins for use in transgenic crops. New proteins with diverse modes of action offer opportunities to control insect pests that are not susceptible to Bt insecticidal proteins and to delay or prevent the potential occurrence of resistance of insects to crops genetically modified with Bt genes. Cholesterol oxidase emerged from our screen as a new insecticidal protein with potent activity against the cotton boll weevil. Cholesterol oxidase was acutely toxic to boll weevil larvae, with an LC50 of 2–6 parts per million when ingested in artificial diet feeding assays, and caused marked reductions in fecundity when ingested by adult boll weevils. Cholesterol oxidase also exerted significant, though less severe, toxicity against several lepidopteran pests. The insecticidal action of cholesterol oxidase appears to be due to oxidation of midgut epithelial membrane cholesterol followed by membrane disruption. A cholesterol oxidase gene was cloned and expressed in transgenic tobacco plants to yield plant tissue that exerted potent activity against boll weevil. Expression of this cholesterol oxidase gene in cotton plants may offer significant protection against the cotton boll weevil and may also aid in the mitigation of resistance of cotton lepidopteran pests to Bt proteins.

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Dean A. Kopsell, Scott McElroy, Carl Sams, and David Kopsell

Vegetable crops can be significant sources of nutritionally important dietary carotenoids and Brassica vegetables are sources that also exhibit antioxidant and anticarcinogenic activity. The family Brassicaceae contains a diverse group of plant species commercially important in many parts of the world. The six economically important Brassica species are closely related genetically. Three diploid species (B. nigra, B. rapa, and B. oleracea) are the natural progenitors of the allotetraploid species (B. juncea, B. napus, and B. carinata). The objective of this study was to characterize the accumulation of important dietary carotenoid pigments among the genetically related Brassica species. The HPLC quantification revealed significant differences in carotenoid and chlorophyll pigment accumulation among the Brassica species. Brassica nigra accumulated the highest concentrations of lutein, 5,6-epoxy lutein, violaxanthin, and neoxanthin. The highest concentrations of beta-carotene and total chlorophyll were found in B. juncea. Brassica rapa accumulated the highest concentrations of zeaxanthin and antheraxanthin. For each of the pigments analyzed, the diploid Brassica species accumulated higher concentrations, on average, than the amphidiploid species. Brassicas convey unique health attributes when consumed in the diet. Identification of genetic relationships among the Brassica species would be beneficial information for improvement programs designed to increase carotenoid values.

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Mark G. Lefsrud and Dean A. Kopsell

Plant growing systems have consistently utilized the standard Earth day as the radiation cycle for plant growth. However, the radiation cycle can easily be controlled by using automated systems to regulate the exact amount of time plants are exposed to irradiation (and darkness). This experiment investigated the influence of different radiation cycles on plant growth, chlorophyll and carotenoid pigment accumulation in kale (Brassica oleracea L. var. acephala D.C). Kale plants were grown in growth chambers in nutrient solution culture under radiation cycle treatments of 2, 12, 24, and 48 h, with 50% irradiance and 50% darkness during each time period. Total irradiation throughout the experiment was the same for each treatment. Radiation cycle treatments significantly affected kale fresh mass, dry mass, chlorophyll a and b, lutein, and beta-carotene. Maximum fresh mass occurred under the 2-h radiation cycle treatment. The maximum dry mass occurred under the 12-h radiation cycle treatment, which coincided with the maximum accumulation of lutein, beta-carotene, and chlorophyll a, expressed on a fresh mass basis. The minimum fresh mass occurred during the 24 h radiation cycle treatment, which coincided with the largest chlorophyll b accumulation. Increased levels of chlorophyll, lutein and beta-carotene were not required to achieve maximum fresh mass production. Environmental manipulation of carotenoid production in kale is possible. Increases in carotenoid concentrations would be expected to increase their nutritional contribution to the diet.

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Krista C. Shellie, Robert L. Mangan, and Sam J. Ingle

The objective of this research was to investigate whether a controlled atmosphere established inside a high temperature forced air chamber could enhance the mortality of the most heat-resistant life stage of Mexican fruit fly larvae (Anastrepha ludens Loew) and thereby reduce the amount of time grapefruit (Citrus paradisi Macf.) harvested from Mexican fruit fly-infested regions must be exposed to high-temperature forced air to achieve quarantine security. The mortality of third instar larvae treated on diet was significantly higher after exposure to 1% oxygen or 1% oxygen enriched with 20% carbon dioxide than it was in either air or air enriched with 20% oxygen. Reducing the amount of oxygen in air from 21% to 1% during forced air heating at 46°C, reduced the exposure time required for 100% kill of larvae inside artificially infested grapefruit from 5 hours to 3.5 hours. Inconsistent fruit quality results warrant further study to optimize controlled atmosphere conditions during heating. Based upon relative levels of carbon dioxide inside the grapefruit during heating, fruit respiration during heating in 1% oxygen was lower than during heating in air. Results from this research suggest that reducing the amount of oxygen in a high temperature forced air chamber during heating can reduce the amount of time fruit must be exposed to heat for quarantine security against Mexican fruit fly.

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Murshidul Hoque*, Husein Ajwa, and Beiquan Mou

Lettuce (Lactuca sativa L.) is an essential salad crop in the American diet. Nitrogen (N), phosphorus (P), and potassium (K) are required for successful lettuce production and can influence lettuce quality. The objective of the study was to evaluate changes in nutritional composition of romaine (`Green Tower') and iceberg (`Sharp Shooter') lettuce in responses to N, P and K fertilization during fall production in Salinas, Calif. Sixteen treatment combinations of fertilizer were selected to provide a range of treatments. N was applied at 0, 112, 225, and 338 kg·ha-1 as ammonium nitrate; P was applied at 0, 112, and 225 kg/ha as super phosphate; and K was applied at 0 and 112 kg·ha-1 as muriate of potash. Nutritional content of fresh tissue of two types of lettuce was analyzed using high performance liquid chromatography (HPLC). Among the parameters analyzed were lutein, beta-carotene, chlorophyll a, and chlorophyll b. Yield was increased with increasing N fertilizer level, but was not affected by P or K application rates. The best post harvest quality, however, was at moderate P application rate. Increasing the N and P rates gradually increased glucose content in lettuce but decreased the shelf life. Significant differences between the two types of lettuce were found in chlorophyll, lutein and beta-carotene content. No significant correlations were found between soil fertilizer application levels and nutritional content of lettuce. However, the ratio of chlorophyll a and b were greater with the increase of fertilizer rate. Nutritional composition including vitamin C will be presented.

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Annette Wszelaki, Karla Deza-Duran, and Carol Harper

Pigeon pea is an important food crop for the Puerto Rican diet, as well as the economy. Pigeon pea ranks fourth in production among edible legumes in production worldwide. It can be consumed dried or as a vegetable (fresh, frozen, or canned). Canned, frozen, and dried peas are commonly used when fresh peas are no longer available. Due to the preferred flavor of fresh pigeon pea, it commands a higher market premium, selling for more than twice the price of the dried product. Although there is a great demand for this vegetable in Puerto Rico, virtually no research has been done on fresh pigeon pea postharvest physiology and its overall keeping quality. Baseline data on pigeon pea physiology, including respiration and ethylene production rates, soluble solids, titratable acidity, color reflectance, chlorophyll content, and responses to ethylene are presented here in order to establish the optimum storage temperature. Using this information, fresh pigeon pea consumption could increase locally, and exporting opportunities for shipping pigeon pea to alternative markets could be expanded.

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Joseph K. Peterson, Howard F. Harrison, D. Michael Jackson, and Maurice E. Snook

Periderm and cortex tissues of 14 genetically diverse sweetpotato [Ipomoea batatas (L.) Lam.] clones were grown under low stress conditions and analyzed for their content of scopoletin ((7-hydroxy-6-methoxycoumarin) and scopolin (7-glucosylscopoletin). A wide range of concentrations of both compounds was found in both tissues. The two compounds were tested in vitro for their biological activity (concentration-activity relationships) using several bio assays: germination of proso-millet (Panicum milliaceum L.) seed; mycelial growth of the sweetpotato fungal pathogens Fusarium oxysporum Schlecht. f. sp. batatas (Wollenw.) Snyd. & Hans, F. solani (Sacc.) Mart., Lasiodiplodia theobromae (Pat.) Griffon & Maubl., and Rhizopus stolonifer (Ehr. ex Fr.) Lind; and growth and mortality of diamondback moth[Plutella xylostella (L.)] larvae on artificial diet. The glycoside scopolin showed little activity, except moderate inhibition of F. oxysporum. The aglycone scopoletin inhibited seed germination and larval growth; however, at much higher concentrations than were measured in the tissues. Mycelial growth of the four pathogenic fungi, however, was inhibited at concentrations occurring in some sweetpotato clones.

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Stephen L. Love, Thomas Salaiz, Bahman Shafii, William J. Price, Alvin R. Mosley, and Robert E. Thornton

Ascorbic acid (vitamin C) is an essential nutrient in the human diet and potatoes are a valuable source. As a first step in breeding for potatoes (Solanum tuberosum L.) with higher levels of ascorbic acid, 75 clones from 12 North American potato-breeding programs were evaluated for concentration, and 10 of those for stability of expression. Trials were grown in Idaho, Oregon, and Washington in 1999 and 2000, tubers sampled, and ascorbic acid quantified. There were significant differences among clones and clone by environment interaction was also significant. Concentration of ascorbic acid of the clones was continuously distributed over a range of 11.5 to 29.8 mg/100 g. A subgroup of 10 clones was analyzed using an additive main effects and multiplicative interaction (AMMI) model, to diagnose interaction patterns and measure clone stability. The first two principal component axes accounted for over 80% of the variability. Bi-plot analysis showed `Ranger Russet' to be highly unstable across the environments tested. A plot of Tai's stability statistics found six of the 10 clones to be stable for ascorbic acid expression. Appropriate evaluation methods for ascorbic acid concentration must involve multi-year testing.