Sara E. Duke

Effect of Racemic and (+)- and (−)-Gossypol on the Survival and Development of Helicoverpa zea Larvae

Gossypol is a sesquiterpene that occurs naturally in seed and other parts of the cotton plant. Because of restricted rotation around the binaphthyl bond, it occurs naturally as enantiomeric mixtures with (+)-gossypol to (−)-gossypol ratios that vary between 97:3 and 31:69. Commercial cotton varieties (Gossypium hirsutum) normally exhibit an approximate 3:2 ratio. (+)-Gossypol is significantly less toxic than (−)-gossypol to nonruminant animals; thus, cottonseed containing high levels of (+)-gossypol might be safely fed to nonruminants. Gossypol, however, is an important component in the cotton plants defense against insect herbivores, but it is not known how cotton plants that exhibit high levels of (+)-gossypol in the foliage might be affected by insect herbivory. To address this question, 1-d-old Helicoverpa zea larvae were fed diets with 0.16, 0.20, and 0.24% racemic, (+)-, and (−)-gossypol. Larval pupal weights, days-to-pupation, and survival were adversely affected by all gossypol diets compared with the control diet. Statistical differences were determined by comparing the compounds among themselves at the three levels and between the three compounds at the same level. When the compounds were compared among themselves, no large differences were observed in pupal weights or in days-to-pupation among any of the diets. Among the three compounds, at the 0.16% level, the diet containing racemic gossypol was the most effective at reducing survival. At the 0.20 and 0.24% levels of racemic (+)- and (−)-gossypol, survival was not statistically different. The overall results indicate that (+)-gossypol is as inhibitory to H. zea larvae as racemic or (−)-gossypol, and thus, cotton plants containing predominantly the (+)-enantiomer in foliage may maintain significant defense against insect herbivory.

Effect of Racemic, (+)- and (−)-Gossypol on Survival and Development of Heliothis virescens Larvae

Gossypol is a constituent of the lysigenous foliar glands of cotton plants and is also found in glands in cottonseed. Gossypol exists as enantiomers because of restricted rotation around the binaphthyl bond. The biological activities of the enantiomers differ. For example, (+)-gossypol can be fed safely to nonruminants such as chickens, but (−)-gossypol cannot. Most commercial cottonseed contain a (+)- to (−)-gossypol ratio of ≈3:2. Conventional breeding techniques can be used to develop cottonseed that contains >95% (+)-gossypol. Notably, gossypol protects the plant from insect herbivores. Herein, we report the effect of various forms of gossypol on Heliothis virescens (Fabricius) larvae. Three levels (0.16, 0.24, and 0.32%) of racemic, (+)-, and (−)-gossypol were added to artificial rearing diets and were fed to H. virescens larvae. All 0.24 and 0.32% gossypol diets significantly lengthened days-to-pupation and decreased pupal weight compared with the control. Percent survival was significantly less for larvae reared on diets containing 0.24% of all three forms of gossypol as compared with the control diet. (+)-Gossypol was superior or equivalent to racemic gossypol as measured by the three parameters studied. Higher concentrations of all gossypol forms were required to reduce survival and pupal weights and increase days-to-pupation for larvae of H. virescens larvae compared with the concentration needed to affect larvae of Helicoverpa zea (Boddie), which was studied previously. These results indicate that current efforts to breed cotton lines containing mostly (+)-gossypol in seed should not significantly impair the plant’s natural defenses against insects.

Development and evaluation of WillTry. An instrument for measuring children's willingness to try fruits and vegetables ☆

This paper describes the development and evaluation of the WillTry instrument, a psychometric tool designed to measure childrens willingness to try fruits and vegetables. WillTry surveys were interviewer-administered to 284 children in an elementary school and summer day camps located in rural Mississippi and Arkansas (United States) communities. Factor analysis was used to determine construct dimensionality. Additional evaluation included internal consistency, test-retest reliability, and predictive validity. Factor analysis suggested a single dimension for the food items. The WillTry food scale had substantial reliability (intraclass correlation coefficients between 0.61 and 0.80) and sufficient internal consistency (Cronbachs alpha > or = 0.70). Results of the regression analysis for percent consumption of foods offered on WillTry response confirmed the predictive validity of the instrument. The results of these analyses provide psychometric evidence for the use of the WillTry instrument as a measure of willingness to try fruits and vegetables in rural, southern US children 5-14 years of age.

Ecophysiological responses of salt cedar (Tamarix spp. L.) to the northern tamarisk beetle (Diorhabda carinulata Desbrochers) in a controlled environment.

The northern tamarisk beetle (Diorhabda carinulata Desbrochers) was released in several western states as a biocontrol agent to suppress Tamarix spp. L. which has invaded riparian ecosystems; however, effects of beetle herbivory on Tamarix physiology are largely undocumented and may have ecosystem ramifications. Herbivory by this insect produces discoloration of leaves and premature leaf drop in these ecosystems, yet the cause of premature leaf drop and the effects of this leaf drop are still unknown. Insect herbivory may change leaf photosynthesis and respiration and may affect a plant’s ability to regulate water loss and increase water stress. Premature leaf drop may affect plant tissue chemistry and belowground carbon allocation. We conducted a greenhouse experiment to understand how Tamarix responds physiologically to adult beetle and larvae herbivory and to determine the proximate cause of premature leaf drop. We hypothesized that plants experiencing beetle herbivory would have greater leaf and root respiration rates, greater photosynthesis, increased water stress, inefficient leaf nitrogen retranslocation, lower root biomass and lower total non-structural carbohydrates in roots. Insect herbivory reduced photosynthesis rates, minimally affected respiration rates, but significantly increased water loss during daytime and nighttime hours and this produced increased water stress. The proximate cause for premature leaf drop appears to be desiccation. Plants exposed to herbivory were inefficient in their retranslocation of nitrogen before premature leaf drop. Root biomass showed a decreasing trend in plants subjected to herbivory. Stress induced by herbivory may render these trees less competitive in future growing seasons.

Crop Performance and Weed Suppression by Weed-Suppressive Rice Cultivars in Furrow- and Flood-Irrigated Systems under Reduced Herbicide Inputs

Abstract Weed control in rice is challenging, particularly in light of increased resistance to herbicides in weed populations and diminishing availability of irrigation water. Certain indica rice cultivars can produce high yields and suppress weeds in conventional flood-irrigated, drill-seeded systems in the southern United States under reduced herbicide inputs, but their response to reduced irrigation inputs in these systems in not known. Rice productivity and weed control by weed-suppressive cultivars and conventional nonsuppressive cultivars were evaluated in a nonflooded furrow-irrigated (FU) system and a conventionally flooded (FL) system under three levels of weed management (herbicide inputs) in a 3-yr field study. Rice yields across all weed management levels yielded ∼ 76% less in the FU system than in the FL system. The allelopathic indica cultivar, ‘PI 312777’, and commercial hybrid rice ‘CLXL729’ generally produced the highest grain yields and greatest suppression of barnyardgrass in both irrigation systems. ‘Bengal’ and ‘Wells’ were the top-yielding conventional cultivars whereas ‘Lemont’ and ‘CL171AR’ yielded the least. Weed suppression by PI 312777 and CLXL729 under “medium” weed management was equivalent to that of Lemont and CL171AR at the “high” management level, suggesting that the weed-suppressive cultivars may be able to compensate for suboptimal herbicide inputs or incomplete weed control. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv; rice, Oryza sativa L., ‘Bengal’, ‘CLXL729’, ‘Lemont’, ‘PI 312777’, ‘Wells’.

First-Year Establishment, Biomass and Seed Production of Early vs. Late Seral Natives in Two Medusahead (Taeniatherum caput-medusae) Invaded Soils

Abstract Re-seeding efforts to restore or rehabilitate Great Basin rangelands invaded by exotic annual grasses are expensive and have generally achieved limited success. There is a need to identify new strategies to improve restoration outcomes. We tested the performance of a native early seral seed mix (annual forbs, early seral grasses and shrubs) with that of a native late seral mix representative of species commonly used in restoration when growing with medusahead in soils of contrasting texture (sandy loam and clay loam) through the first growing season after seeding. Natives were also seeded without medusahead. We found that the grasses and forbs in the early seral mix established significantly better than those in the late seral mix, and the early seral mix significantly reduced aboveground biomass and seed production of medusahead by 16 and 17% respectively, likely because of competition with the early seral native forb, bristly fiddleneck. Medusahead performance was reduced in both soil types, suggesting utility of bristly fiddleneck in restoration is not limited to only one soil type. In contrast, the late seral mix did not suppress medusahead establishment, aboveground biomass or seed production. Although the native perennial grasses, particularly early seral species, were able to establish with medusahead, these grasses did not appear to have a suppressive effect on medusahead during the first growing season. Medusahead was able to establish and produce seeds on both soil types, demonstrating an ability to expand its current range in the Intermountain West, though aboveground biomass and seed production was higher in the clay loam. Our results suggest that certain species may play a key role in restoration, and that targeting early seral species in particular to find additional native species with the ability to suppress exotic annual grasses is an important next step in improving restoration outcomes in desert ecosystems. Nomenclature: Medusahead (Taeniatherum caput-medusae (L.) Nevski), bristly fiddleneck (Amsinckia tessellata A. Gray). Management Implications: Medusahead is an exotic annual grass that that has invaded into the Intermountain West of the U.S., reducing native species biodiversity and increasing fire frequency. In a study of native and medusahead performance, we found that the early seral native annual forb, bristly fiddleneck, was an effective competitor with medusahead in two soil types, significantly reducing biomass and seed production by 16 to 17%. Given that this effect was relatively small, further research to examine whether the use of increased seeding density of bristly fiddleneck and/or whether greater diversity of species in the seeding mix would enhance exotic suppression is warranted. Native perennial grasses, particularly early seral grasses, established in higher numbers than native forbs and shrubs, demonstrating their importance in restoration seedings. Although they did not appear to have a suppressive effect on medusahead during their first growing season, perennial grasses have been found to be effective competitors with exotic annual grasses once mature. Our findings suggest that efforts to find additional novel candidate species for seed mixtures may be best focused on early successional species, similar to bristly fiddleneck, to improve restoration/rehabilitation outcomes in disturbed rangeland ecosystems.

Rangeland Vegetation and Soil Response to Summer Patch Fires Under Continuous Grazing

Prescribed fire is used to reduce woody plant and cactus cover and restore degraded rangelands in the southern Great Plains, but little is known regarding the impact of summer fires. We evaluated the effects of summer fires applied as patch burns in continuously grazed rangeland in north Texas. Vegetation and soil responses were measured on patches burned within grazing units in the summers of 1998, 1999, and 2000 relative to that on adjacent unburned control areas in the same grazing units. Annual rainfall during the study was below average for six burns (1998 and 1999) and average or above for three burns (2000). If average rainfall preceded and followed summer burning, degradation was limited to a modest increase in bare ground which recovered to exceed unburned control levels within 2 years. However, when drought conditions preceded and followed burning, there was an increase in bare ground and the proportion of annual forbs and annual grasses at the expense of perennial grasses. These areas took 3–5 years to recover. Areas burned in any year did not recover until after a season of favorable precipitation. The degree of degradation was proportional to the severity of drought conditions. The fires reduced the cover of honey mesquite (Prosopis glandulosa Torr.), other shrubs and cactus (Opuntia spp.), which facilitated herbaceous recovery, mitigating the negative impacts of burning in summer and the increased herbivory on the burned patches. Increases in herbaceous species composition were positively related to woody plant and cactus reduction following fire treatment. Results suggest that summer burning may be an effective and low-cost means of controlling problem plants, increasing pasture heterogeneity, and reducing herbivore impact on intensively grazed patches. However, before the practice of summer burning can be advocated, research needs to determine if post-burn deferment will facilitate more rapid recovery through regulating herbivory after burning to increase the recovery of litter and herbaceous cover and restore desired herbaceous species composition and production.

Temporal Variability in Microclimatic Conditions for Grass Germination and Emergence in the Sagebrush Steppe

ABSTRACT Sagebrush steppe ecosystems in the western United States are characterized by harsh environmental conditions with high annual and seasonal variability in both precipitation and temperature. Environmental variability contributes to widespread failure in establishing stands of desired species on degraded and invaded landscapes. To characterize seasonal microclimatic patterns and planting date effects on restoration outcomes, we evaluated long-term simulations of seed germination response of cheatgrass (Bromus tectorum L.), bottlebrush squirreltail (Elymus elymoides [Raf] Swezey), and Idaho fescue (Festuca idahoensis Elmer) to annual patterns of soil temperature and moisture. Extremely high annual variability in both the conditions favorable for germination and patterns of post-germination drought and thermal stress make it difficult to justify general inferences about seedbed treatment and planting date effects from individual, short-term field studies. We discuss the interpretation of individual-year and seasonal plant establishment factors and offer a mechanistic model for interpreting planting date and year effects on initial seedling establishment. Historical ranking and mechanistic descriptions of individual-year seedbed conditions may allow for expanded inferences through meta-analysis of limited-term field experiments.

Conversion of Fusaric Acid to Fusarinol by Aspergillus tubingensis: A Detoxification Reaction

The fungus Fusarium oxysporum causes wilt diseases of plants and produces a potent phytotoxin fusaric acid (FA), which is also toxic to many microorganisms. An Aspergillus tubingensis strain with high tolerance to FA was isolated from soil and designated as CDRAt01. HPLC analysis of culture filtrates from A. tubingensis isolate CDRAt01 grown with the addition of FA indicated the formation of a metabolite over time that was associated with a decrease of FA. Spectral analysis and chemical synthesis confirmed the compound as 5-butyl-2-pyridinemethanol, referred to here as fusarinol. The phytotoxicity of fusarinol compared to FA was measured by comparing necrosis induced in cotton (Gossypium hirsutum L. cv. Coker 312) cotyledons. Fusarinol was significantly less phytotoxic than FA. Therefore, the A. tubingensis strain provides a novel detoxification mechanism against FA which may be utilized to control Fusarium wilt.

Detoxification of Fusaric Acid by the Soil Microbe Mucor rouxii

Fusarium oxysporum f. sp. vasinfectum race 4 (VCG0114), which causes root rot and wilt of cotton (Gossypium hirsutum and G. barbadense), has been identified recently for the first time in the western hemisphere in certain fields in the San Joaquin Valley of California. This pathotype produces copious quantities of the plant toxin fusaric acid (5-butyl-2-pyridinecarboxylic acid) compared to other isolates of F. oxysporum f. sp. vasinfectum (Fov) that are indigenous to the United States. Fusaric acid is toxic to cotton plants and may help the pathogen compete with other microbes in the soil. We found that a laboratory strain of the fungus Mucor rouxii converts fusaric acid into a newly identified compound, 8-hydroxyfusaric acid. The latter compound is significantly less phytotoxic to cotton than the parent compound. On the basis of bioassays of hydroxylated analogues of fusaric acid, hydroxylation of the butyl side chain of fusaric acid may affect a general detoxification of fusaric acid. Genes that control this hydroxylation may be useful in developing biocontrol agents to manage Fov.