Twin-screw extrusion of ‘Pesta’-encapsulated biocontrol agents

World Journal of Microbiology and Biotechnology -     

Bioherbicidal potential of a strain of Xanthomonas spp. for control of common cocklebur (Xanthium strumarium)

Several isolates of a previously unreported bacterial pathogen were discovered on common cocklebur seedlings in Chicot County, AR and Washington County, MS. Diseased plants in nature exhibited angular-shaped leaf spotting symptoms on leaf margins and central leaf areas. The isolates were cultured from diseased leaf tissue and tentatively identified as Xanthomonas spp., and their virulence on common cocklebur seedlings compared. The most virulent isolate (LVA987) was used in studies to define disease progression on cocklebur seedlings and to carry out a host range evaluation on various weeds and crop plants. High virulence was found on common cocklebur > marestail (Conyza canadensis) > giant ragweed (Ambrosia trifida) ≥ and common ragweed (Ambrosia artemisifolia). These results suggest this pathogen may be useful for the biological control of these important species of weeds. This is also highly relevant since all of these weeds have evolved resistance to one or more synthetic herbicides and are thus becoming more difficult to control with conventional herbicides.     

Evaluation of the bioherbicide Myrothecium verrucaria for weed control in tomato (Lycopersicon esculentum)

An isolate of the fungus Myrothecium verrucaria was evaluated for its biocontrol potential against common purslane, horse purslane, spotted spurge, and prostrate spurge, all serious weed pests in commercial tomato fields in the southeastern US. In greenhouse and field tests, M. verrucaria was highly virulent against these weeds when applied as conidial sprays formulated in 0.2% Silwet L-77 surfactant, even in the absence of dew. In field test plots naturally infested with these weeds, seedlings in the two-to-three leaf growth stage treated with M. verrucaria at 2×10⁷ conidia mL^-1 in 0.2% Silwet, exhibited leaf and stem necrosis within 24 h following inoculation, with mortality occurring within 96 h. After 7 days, M. verrucaria had killed 90-95% of both purslane species and 85-95% of both spurge species. Tomatoes that were transplanted into plots treated with M. verrucaria remained healthy and vigorous throughout the growing season. Since M. verrucaria effectively controlled several common weeds under field conditions, this fungus appears to have potential as an effective bioherbicide for pre-plant weed control in production systems with transplanted tomato.     

Effect of row spacing on biological control of sicklepod (Senna obtusifolia) with Colletotrichum gloeosporioides

In field experiments conducted over 3 years, the mycoherbicidal fungus Colletotrichum gloeosporioides, formulated either in 20% (v/v) unrefined corn oil and 0.2% Silwet L-77 surfactant or with an invert emulsion, provided season-long control of Senna obtusifolia in narrow (51 cm) rows of soybean. However, in wide (102 cm) rows, one application of either formulation failed to provide season-long control of S. obtusifolia, and two applications were required to achieve season-long weed control. In narrow (51 cm) rows, one application of the fungus either in unrefined corn oil or an invert emulsion controlled S. obtusifolia an average of >90%, and a second application was not required for season long weed control. Soybean yields in wide-row plots treated with two applications of either the fungus/corn oil or fungus/invert emulsion, or with a single application of the fungal treatments in narrow-row soybean plots, were not significantly different from weed-free control plots, or from plots treated with the herbicide chlorimuron. These results suggest that row spacing can affect mycoherbicidal efficacy of this fungus for controlling S. obtusifolia.     

A comparison of chemical pretreatment methods for improving saccharification of cotton stalks

The effectiveness of sulfuric acid (H(2)SO(4)), sodium hydroxide (NaOH), hydrogen peroxide (H(2)O(2)), and ozone pretreatments for conversion of cotton stalks to ethanol was investigated. Ground cotton stalks at a solid loading of 10% (w/v) were pretreated with H(2)SO(4), NaOH, and H(2)O(2) at concentrations of 0.5%, 1%, and 2% (w/v). Treatment temperatures of 90 degrees C and 121 degrees C at 15 psi were investigated for residence times of 30, 60, and 90 min. Ozone pretreatment was performed at 4 degrees C with constant sparging of stalks in water. Solids from H(2)SO(4), NaOH, and H(2)O(2) pretreatments (at 2%, 60 min, 121 degrees C/15 psi) showed significant lignin degradation and/or high sugar availability and hence were hydrolyzed by Celluclast 1.5L and Novozym 188 at 50 degrees C. Sulfuric acid pretreatment resulted in the highest xylan reduction (95.23% for 2% acid, 90 min, 121 degrees C/15 psi) but the lowest cellulose to glucose conversion during hydrolysis (23.85%). Sodium hydroxide pretreatment resulted in the highest level of delignification (65.63% for 2% NaOH, 90 min, 121 degrees C/15 psi) and cellulose conversion (60.8%). Hydrogen peroxide pretreatment resulted in significantly lower (p相似文献   

Hemp sesbania (Sesbania exaltata) control in rice (Oryza sativa) with the bioherbicidal fungus Colletotrichum gloeosporioides f. sp. aeschynomene formulated in an invert emulsion

In greenhouse and field experiments, an invert emulsion (MSG 8.25) was tested with dried, formulated spores of the bioherbicidal fungus Colletotrichum gloeosporioides f. sp. aeschynomene, a highly virulent pathogen of the leguminous weed Aeschynomene virginica (northern jointvetch), but considered ‘immune’ against another more serious leguminous weed, Sesbania exaltata (hemp sesbania). A 1:1 (v/v) fungus/invert emulsion mixture resulted in 100% infection and mortality of inoculated hemp sesbania seedlings over a 21-day period under greenhouse conditions. In replicated field tests of the fungus/invert formulation conducted in Stuttgart, AR, and Stoneville, MS, hemp sesbania was controlled 85 and 90%, respectively. These results suggest that this invert emulsion expands the host range of C. gloeosporioides f. sp. aeschynomene, with a concomitant improvement of the bioherbicidal potential of this pathogen.     

Autonomy,Equality, and Teaching among Aka Foragers and Ngandu Farmers of the Congo Basin

The significance of teaching to the evolution of human culture is under debate. We contribute to the discussion by using a quantitative, cross-cultural comparative approach to investigate the role of teaching in the lives of children in two small-scale societies: Aka foragers and Ngandu farmers of the Central African Republic. Focal follows with behavior coding were used to record social learning experiences of children aged 4 to 16 during daily life. “Teaching” was coded based on a functional definition from evolutionary biology. Frequencies, contexts, and subtypes of teaching as well as the identity of teachers were analyzed. Teaching was rare compared to observational learning, although both forms of social learning were negatively correlated with age. Children received teaching from a variety of individuals, and they also engaged in teaching. Several teaching types were observed, including instruction, negative feedback, and commands. Statistical differences in the distribution of teaching types and the identity of teachers corresponded with contrasting forager vs. farmer foundational cultural schema. For example, Aka children received less instruction, which empirically limits autonomous learning, and were as likely to receive instruction and negative feedback from other children as they were from adults. Commands, however, exhibited a different pattern suggesting a more complex role for this teaching type. Although consistent with claims that teaching is relatively rare in small-scale societies, this evidence supports the conclusion that teaching is a universal, early emerging cognitive ability in humans. However, culture (e.g., values for autonomy and egalitarianism) structures the nature of teaching.     

Bioherbicidal enhancement and host range expansion of a mycoherbicidal fungus via formulation approaches

Eastern black nightshade (Solanum ptycanthum; EBN) is a problematic weed partly due to its tolerance or resistance to certain herbicides. We examined the effects of an invert emulsion (IE) on the host range and weed control efficacy of the fungus Colletotrichum coccodes (NRRL strain 15547) for biocontrol of EBN. Greenhouse tests demonstrated that several other solanaceous weeds were also infected and killed, and field tests revealed >90% EBN control and dry weight reduction in plants treated with the fungus-IE formulation. These results demonstrate that this IE formulation can promote the efficacy of this bioherbicidal pathogen.     

Macrocyclic trichothecenes are undetectable in kudzu (Pueraria montana) plants treated with a high-producing isolate of Myrothecium verrucaria.

Myrothecium verrucaria was found to be an effective pathogen against kudzu grown in the greenhouse and the field. M. verrucaria produced large amounts of macrocyclic trichothecenes when cultured on solid rice medium, including epiroridin E (16.8 mg/g crude extract), epiisororidin E (1 mg/g), roridin E (8.7 mg/g), roridin H (31.3 mg/g), trichoverrin A (0.6 mg/g), trichoverrin B (0.1 mg/g), verrucarin A (37.4 mg/g), and verrucarin J (2.2 mg/g). Most of these toxins were also isolated from M. verrucaria spores and mycelia grown on potato dextrose agar medium, including epiroridin E (32.3 mg/g), epiisororidin E (28.6 mg/g), roridin E (0 mg/g), roridin H (60 mg/g), trichoverrin A (1.3 mg/g), trichoverrin B (1.8 mg/g), verrucarin A (13.8 mg/g), and verrucarin J (131 mg/g). When M. verrucaria was cultured on liquid media, the numbers but not the amounts of toxins decreased. Only epiroridin E (28.3 mg/g), epiisororidin E (29.6 mg/g), verrucarin B (195 mg/g) and verrucarin J (52.6 mg/g) were measured when the fungus was cultured on cornsteep medium. On soyflour-cornmeal broth M. verrucaria produced several toxins, including epiroridin E (58.1 mg/g), epiisororidin E (5.8 mg/g), verrucarin B (29.9 mg/g) and verrucarin J (32 mg/g). In contrast, no macrocyclic trichothecenes were detected by HPLC analysis of plant tissues of kudzu, sicklepod, and soybean treated with aqueous suspensions of M. verrucaria spores formulated with a surfactant. Chloroform-methanol extracts of kudzu leaves and stems treated with M. verrucaria spores were less cytotoxic to four cultured mammalian cell lines than the corresponding extracts from control plants. Purified macrocyclic trichothecenes (verrucarin A and T-2 toxin) were very cytotoxic to the same cell lines (< or = 2 ng/ml). These results show that neither intact macrocyclic trichothecenes nor toxic metabolites could be detected in plant tissues after treatment with M. verrucaria spores. These results argue for both safety and efficacy for the use of M. verrucaria in biological control of kudzu and other noxious weeds, and support proceeding to animal feeding trials for further evaluation of safety.     

Water Activity and Other Factors that Affect the Viability of Colletotrichum truncatum Conidia in Wheat Flour-Kaolin Granules ('Pesta')

Optimization of shelf-life is critically important for biocontrol products containing living microorganisms. Conidia of Colletotrichum truncatum, a fungal pathogen of the weed, hemp sesbania (Sesbania exaltata), were produced in shake flasks (corn meal-soya flour medium) and on Emerson Yp Ss agar and formulated in wheat flour-kaolin granules ('Pesta'). The granules were conditioned at water activities of 0, 0.12, 0.33, 0.53 and 0.75 during storage at 25 C over desiccant or saturated salt solutions. The longest shelf-life (conidial inoculum viability) was found in samples in the water activity range 0-0.33, where the water was bound by the matrix and not readily available to the fungus. At a water activity of 0.12, granules were 100% viable (on water agar) for at least 24 weeks, and were 87% viable after 1 year. Sucrose (5% w/w) partially counteracted the detrimental effect of high water activity on the shelf-life of C. truncatum when incorporated in the granules.