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.
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.
One of the major misconceptions in contemporary society is the widespread belief that our food supply is unsafe. The public's perception of risk is quite different than scientific assessment of risk. While scientists see microbial contamination as the key issue (100 to 10,000X greater risk than from exposure to pesticide residues), consumers appear to be most concerned about the effects of synthetic pesticides and fertilizers in the food they buy. Consumers equate “synthetic” with harmful or bad and “natural” with safe or good, yet they ignore the fact that 99.9% of all pesticides humans are exposed to are naturally occurring. Americans eat approximately 1.5 g. of natural pesticides per person per day, or about 10,000 times more than synthetic pesticide residues. Although few plant toxins have been tested for carcinogenicity so far, of those tested about half are rodent carcinogens. Contrary to public perception, environmental pollution accounts for only 2% of all cancers. By contrast, smoking, diet and other personal lifestyle choices account for more than 75%.
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.
Japanese beetles (JB), Popillia japonica Newman, are destructive, highly polyphagous herbivores that show a general preference for Rosaceous plants. Choice and nochoice feeding assays were conducted to determine the level of resistance among 10 taxa of Malus spp. Mill. Under no-choice conditions, M. baccata (L.) Borkh. `Jackii', M. × `Hargozam' Harvest Gold and M. transitoria (Balatin) Schneider `Schmitcutleaf' Golden Raindrops were highly resistant, with <2 cm2 leaf area consumed in 24 hours. M. × `Radiant' was highly susceptible, with 7.6 cm2 consumed, and the remaining six cultivars were intermediate. Under choice conditions, eight taxa were resistant with <10% defoliation, M. × `Red Splendor' was intermediate with 26%, and M. × `Radiant' was susceptible with 73% defoliation. Feeding responses to eight individual phenolics were tested in artificial diets over a range from 0 to 100 mm. Phloridzin, phloretin, naringenin, and catechin were all feeding deterrents, whereas quercetin and rutin were feeding stimulants. Chlorogenic acid stimulated feeding at low concentrations and deterred feeding at higher concentrations (i.e., a peak response). Kaempferol had no effect. Analysis of endogenous foliar phenolics showed considerable variation in concentrations among taxa. Stepwise multiple regression analysis identified phloridzin as the only endogenous phenolic that was significantly related to resistance under both choice and no-choice feeding conditions.
As humans explore the solar system, life support will need to be increasingly self-sufficient. Growing higher plants and using recycling technologies can improve self-sufficiency. Sodium is an essential mineral for humans, but not typically for plants. Recycling sodium back to humans through food crops may reduce the need for sodium supplements in the human diet. However, if sodium from waste streams is added to the plant system in greater quantities than it is removed, then plant toxic levels may result. The recommended daily sodium requirement is 3000 mg per person. Based on a 20-m2 growing area per person, 150 mg·m–2 sodium would need to be removed each day. Most crops will not remove enough salt when grown at very low sodium levels; however, when grown in 20 mM sodium, plant uptake may meet the 3000 mg/d human sodium requirement without affecting yields. We grew four different salad crops (lettuce, radish, spinach, and table beet) hydroponically and calculated plant uptake rates and partitioning with 0, 20, 40, or 80 mM sodium supplemented nutrient solutions (corresponding to ≈1.4, 4.0, 8.0, and 13.0 dS·m–1 electrical conductivity). Sodium at 40 and 80 mM reduced edible yields. Sodium replaced tissue potassium in most cases, whereas calcium and magnesium concentrations were much less affected, particularly at 20 mM sodium. This data will be used to model sodium flows within a bioregenerative life support system and determine the feasibility of sodium recycling using food crops.
European corn borer, Ostrinia nubilalis Hübner, can severely affect sweet corn quality. Selection techniques in field experiments have improved ear feeding resistance associated with morphological features and/or allelochemicals. The isolation and identification of allelochemicals that detrimentally affect O. nubilalismay improve breeder selection for host plant resistance, thus reducing the need for insecticide application. A laboratory bioassay was used to detect chemical resistance factors in silk and kernel tissues of 10 variously resistant sweet corn genotypes. Ground lyophilized tissue from field-grown plants was added to a nutritionally complete larval diet before infestation with O. nubilalis neonates. Larval weights on a 10-day basis and time to pupation were recorded to estimate larval development. Tissue and genotype main effects affected (P ≤ 0.05) 10-day larval weight and time to pupation. Silk tissue (P ≤ 0.05) reduced 10-day larval weight and increased the time to pupation compared with kernel tissue and the cellulose control, which did not differ. Silk tissue reduced larval weight by 65% and increased time to pupation by 4.0 days compared with the cellulose control. Genotypes variously affected (P ≤ 0.05) larval growth and development, reducing 10-day larval weight up to 51% and increasing the time to pupation up to 4.2 days when comparing the best genotype for each developmental stage with the cellulose control. Silk tissue of some genotypes may contain allelochemicals that decrease the rate of larval growth and development. The status of allelochemical detection in silk tissue will be discussed.
Extensive epidemiological evidence suggests that carotenoids (including vitamin A), ascorbate (vitamin C), tocols (including vitamin E), and glucosinolate breakdown products exert anticarcinogenic effects in a range of human tissues. Consumption of fresh and processed vegetables with enhanced levels of these phytochemicals could reduce human risk of cancer. The vitamins play a major role as antioxidants, offering protection against cancer by preventing or reversing oxidative damage to DNA and other cellular components. Cruciferous vegetables contain glucosinolates (GSs), which, during mastication, are hydrolyzed by the enzyme myrosinase into bioactive breakdown products (BBPs), including sulforaphane. BBPs appear to induce synthesis of drug metabolism enzymes resulting in increased detoxification rates of carcinogens. This paper describes an interdisciplinary investigation designed to develop vegetable cultivars that offer chemoprotection from cancer at doses commensurate with a normal American diet. Initial work has focused on surveying sweet corn and Brassicae oleraceae germplasm for variation in vitamin and glucosinolate content in conjunction with in vitro and in vivo bioassays to determine which compounds and concentrations optimize chemoprotectant activity. Segregating populations from crosses between sweet corn and Brassica lines that vary in vitamin and GS concentrations will be assayed for chemical content and chemoprotectant activity, and genetically characterized using DNA marker technology to identify and map genes controlling these traits. This information will improve selection methodology in a breeding program aimed to develop brassica and sweet corn germplasm with enhanced cancer chemoprevention.
Carotenoids are important phytochemical components of our diet and have gained recent attention as important nutritive compounds found mainly in fruits and vegetables with red, orange, and yellow hues. Lycopene is often cited as being inversely correlated with the occurrence of various cancers, in lowering rates of cardiovascular disease, and improving other various other immune responses. Antioxidant activity, specifically oxidative radical quenching power, is the putative rationale for carotenoids' involvement in disease risk reduction. It is unlikely, however, that carotenoid content and antioxidant capacity are directly correlated in the whole food since there are other antioxidants present in watermelon, such as various free amino acids. A total measure of antioxidant potential may prove to be a useful tool for measuring watermelon nutritional value and implementing pursuant breeding goals. One assay that has gained recent popularity is the oxygen radical absorbance capacity (ORAC) assay. ORAC includes two assays that separate lipophylic and hydrophilic antioxidants. Currently, most ORAC protocols use isolated compounds or freeze-dried fruit or vegetable samples. Here, the application of a standard hexane-type extraction method, which is more amenable to whole food carotenoid-containing samples, was investigated as a candidate extraction method for the ORAC assay. Variants of this method as well as of the standard ORAC extraction were compared for extraction efficiency. Finally, ORAC values were correlated with carotenoid content and shown to hold a loose negative correlation. Possible reasons for this are considered and discussed.
The world produces adequate food for everyone, but unequal distribution has created a gap between the countries that produce more food than they consume and those countries with deficit production. About 815 million people suffer from hunger and malnutrition, mostly in the developing world. By 2020, the developing world is expected to face the overwhelming challenge of a 97.5% increase in population; moreover, developing countries will face serious challenges with the trend of a major shift in population from rural to urban areas, where 52% of the people will live in megacities—all asking for more food, land, and infrastructure. According to the World Health Organization, an estimated 334 million children in developing countries are malnourished. In 2020, one out of every four children in these countries will still be malnourished. It is recognized that modern agriculture must diversify production and achieve sustainable higher output to supplement food security. In order to reduce pressure on cereals as well as to improve human nutrition through the consumption of other nutritious crops, diversification in cropping patterns can provide better options. The increased production and consumption of fruits and vegetables, with their wide adaptation and providers of important nutrients (especially vitamins and minerals), offer promise for the future. Fruits and vegetables as food and diet supplements are gaining momentum in most countries. In addition, recent experimental evidence has shown the growing importance of fruits and vegetables in the prevention of noncommunicable diseases. Further, horticulture would play an important role in urban and peri-urban agriculture and development.