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The fungal genus Myrothecium was once polyphyletic but a recent reconsideration of the family Stachybotryaceae spilt it into several genera. The ex-neotype specimen of the species Myrothecium verrucaria is now recognized as Albifimbria verrucaria. The well-studied plant pathogen and candidate bioherbicide CABI-IMI 368023, previously identified as M. verrucaria, was analyzed morphologically and genetically and found to be most consistently aligned with the other representatives of A. verrucaria.

Spore formulations of the bioherbicidal fungus Colletotrichum gloeosporioides f. sp. aeschynomene (ATCC No. 20358) (CGA) were evaluated for control of three weed species: northern jointvetch (Aesch...

The shelf-life of a bioherbicide product is an important factor with regard to its commercial potential. The bioherbicidal efficacy of freshly fermented Myrothecium verrucaria (strain IMI 368023) (MV) mycelia formulations and MV mycelia preparations that had been freeze-dried and then stored at -20°C for 8 years was compared. Two concentrations of each formulation (1.0x and 0.5x) were tested, utilizing bioassays on seedlings of the weed, hemp sesbania (Sesbania exaltata) under greenhouse conditions or in darkness utilizing hydroponically grown seedlings. Freeze drying of freshly prepared MV mycelium produced a light, brownish-colored powder. Efficacy tests of this reconstituted 8-year-old dried material showed that some bioherbicidal activity was lost during long-term storage, i.e., ~20% and ~60% seedling dry weight reduction at the 1.0x and 0.5x rate, respectively. Although plant mortality was greater in the fresh mycelial preparations treatments versus the freeze-dried and stored samples at all time points in the time-course, the stored material still caused >80% mortality, 15 days after treatment. Comparative disease progression ratings also showed a similar trend. Overall results show that freeze-drying MV is a useful method to reduce the bulk and cumbersomeness of storing heavy liquid fermentation product, while retaining bioherbicidal activity. These findings increase the utility of this bioherbicide and offer the potential to use the dried material in soil treatments or in a more concentrated form than attainable via the fermented product.

The effects of environmental parameters on bioherbicidal activity of the bacterium Xanthomonas campestris, against glyphosate-resistant and – susceptible Conyza canadensis (horseweed), were studied under greenhouse conditions. Rosette leaf-stage plants were more susceptible than older plants, and increasing inoculum from 105 to 109 cells/mL caused significantly greater plant mortality and biomass reduction of plants in both the rosette and bolting growth stages. A dew period at 25°C was required to cause an 80% and 60% mortality of plants in the rosette and bolting growth stages, respectively. Results indicate that X. campestris can infect and kill horseweed, demonstrating its bioherbicidal potential.

Colletotrichum truncatum was grown on kernels of eight different grains for 3 or 4 weeks at room temperature (22-24°C). Fresh preparations of conidia as well as fungus-infested corn and rice suspensions resulted in 100% mortality of hemp sesbania seedlings when sprayed postemergence with a 14 h dew period. Fresh preparations of mycelia and fungus-infested sorghum suspensions resulted in 90 and 65% mortality of hemp sesbania seedlings, respectively. Lower mortality ( &#104 15%) occurred with the other ground fungus-infested grain suspensions. Fresh preparations of conidia, fungus-infested corn, rice and sorghum, and mycelia, when applied to soil pre-emergence, resulted in 100, 94, 100, 83 and 71% mortality of hemp sesbania seedlings 14 days after application, respectively. Lower mortality ( &#104 23%) occurred with the other ground fungus-infested grain preparations. Freshly-prepared C. truncatum at 6.25, 12.5, 25 and 50 mg fungus-formulated rice cm -2 of soil surface, applied pre-emergence or at the ...

A simple method, 'Stabileze', is described for granulating fungi with water-absorbent starch, sucrose, corn oil and silica. The potential biological control fungi, Colletotrichum gloeosporioides and Fusarium oxysporum , were stabilized using this protocol. Bioassays were performed on C. gloeosporioides and showed retention of pathogenicity. Sucrose and oil were tested for their effects on the viability of F. oxysporum over time, and sucrose appears to be the most beneficial factor.

Five fungal biocontrol agents useful in agriculture were grown on rice flour in plastic bags. The flour, infested with Colletotrichum truncatum, an Alternaria sp., Paecilomyces fumosoroseus, or atoxigenic Aspergillus flavus and A. parasiticus, was mixed with wheat flour, kaolin, and water and extruded into granules. The inoculum survived extrusion and fluid bed drying at 50°C 3–92 times better than inoculum produced in liquid fermentation. Depending on the agent, the high level of flour infestation permitted a 1:9 to 1:1600 dilution to yield the 1×106 cfu/g in the final product which is usually needed for biocontrol efficacy. © Rapid Science Ltd. 1998

'Pesta' granules in which fungal propagules are encapsulated in a wheat gluten matrix were prepared in multi-pound quantities by twin-screw extrusion and fluid bed drying. Dough formulations for extrusion contained wheat flour and kaolin, or wheat flour, kaolin and rice flour, plus water and fungal inoculum. Conidial inoculum of Colletotrichum truncatum, a pathogen of the weed hemp sesbania (Sesbania exaltata), survived laboratory scale dough preparation [100% retention of colony-forming units (c.f.u.)] better than dough preparation for twin-screw extrusion (8-10% c.f.u. retention). The loss in viability was linked to the lower water content of dough used in the twin-screw extruder. Fluid bed drying reduced viability further to 1%. Retention of viability after twin-screw extrusion and fluid bed drying at 35-50 °C was 35% with Alternaria conjuncta/infectoria, a pathogen of swamp dodder (Cuscuta gronovii). Retention was 86-100% with atoxigenic strains of Aspergillus flavus and Aspergillus parasiticus used as biocompetitors to reduce aflatoxin levels in peanuts. In the greenhouse, twin-screw-extruded granules containing C. truncatum (at about 5 x 10 4 c.f.u. g -1 ) caused high levels of infection and mortality in hemp sesbania seedlings.

Maintaining adequate viability of microorganisms in products for biocontrol is critically important for commercial reasons. Microsclerotia (MS) of the mycoherbicide agent, Colletotrichum truncatum, are its hardy, over-wintering fungal structures. Microsclerotial inoculum at 2, 7, and 23 MS/granule were matrix-encapsulated in wheat flour–kaolin granules (‘Pesta’), in which the flour provided gluten for the matrix and a food base for the fungus. Pesta granules were dried to a water activity of 0.18–0.29. After storage for 52 weeks at 25°C, granules containing 7 and 23 MS were 100% viable and granules with 2 MS were 95% viable. Granules with 7 MS were 50% viable after 36 weeks at 35°C. Pesta granules (440 granules/g) with conidial inoculum at 3.3×105 c.f.u./g were less storage-stable than granules at the 2 MS/granule level. At all MS inoculum levels, granules stored for up to 2years produced 108 c.f.u./g in vitro when incubated on water agar. High water activity was detrimental to long-term viability. In the greenhouse, 7 MS/granule samples controlled 94% of hemp sesbania when incorporated into the soil pre-planting. The strategy of encapsulation of the naturally stable C. truncatum MS and drying to a favourable water activity led to excellent shelf-life for a live biocontrol agent.

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.

Natural products of an isolate of Fusarium solani App. & Wr. NRRL 18883 grown on rice medium were discovered to be phytotoxic to morningglory. This isolate was evaluated for biocontrol potential on morningglory species including ivyleaf [Ipomoea hederacea (L.) Jacq.], multicoloured (I. tricolor Cav.), paimleaf (I. wrightii Gray), pitted (I. lacunosa L.), purple moonflower (I. turbinata Lag.), red (I. coccinea L.), sharppod (I. cordatotriloba Dennstedt), smallflower (Jacquemontia tamnifolia (L.) Griseb], and tall [I. purpurea (L.) Roth] morningglory. When sprayed at a concentration of 10 g fungus‐infested rice per 50 ml of water, this isolate caused phytotoxic damage including necrosis, chlorosis, growth inhibition, and mortality. Deleterious effects were recorded in all species, ranging from necrotic spots to death, depending on the species. Mortality ranged from 0% at 3 weeks for purple moonflower to 89% for smallflower morningglory. Soil‐drench application (10–20 ml fungal material per 150 g so...

AAL-toxin, produced byAlternaria alternata, was investigated for its phytotoxic effects on 86 crop and weed species. On susceptible tomato leaf discs, AAL-toxin caused electrolyte leakage and chlorosis at 0.01 μM in 24 h. Plants tested exhibited a range of response. AAL-toxin damaged sensitive plants at 5 μM while other plants showed minimal damage at > 1000 μM. Cotton and the important weeds, Canada thistle, field bindweed, and velvetleaf were largely unaffected. Monocots tested were largely immune.

In greenhouse tests, the host specificity of Alternaria crassa (Sacc.) Rands, a mycoherbicide for jimsonweed was altered by the addition of water-soluble filtrates of jimsonweed and hemp sesbania or fruit pectin to fungal conidia suspensions. Several crop and weed species that were resistant to the fungus alone exhibited various degrees of susceptibility following these amendments, with 100% mortality occurring to the weeds hemp sesbania, showy crotalaria, and eastern black nightshade when treated with the fungus/pectin mixture. Nonhost plants that were inoculated with conidial mixtures amended with sucrose or cellulose were not affected. Modification of host specificity of this pathogen could have an influence on its bioherbicidal potential. Nomenclature: Jimsonweed, Datura stramonium L. #3 DATST; hemp sesbania, Sesbania exaltata Rydb. ex A. W. Hill # SEBEX; eastern black nightshade, Solanum ptycanthum Dun. # SOLPT; showy crotalaria, Crotalaria spectabiis Roth, # CVTSP. Additional index words: Biological control, mycoherbicide, host selectivity alteration, DATST, SEBEX, SOLPT, CVTSP.

A strain of Fusarium oxysporum was isolated from infected sicklepod stems in Stoneville, MS, in 1989. When formulated as granules either in a fungus-infested rice preparation or encapsulated in a wheat-gluten matrix called 'Pesta', biocontrol of sicklepod, coffee senna, and hemp sesbania was achieved with preemergence or preplant-incorporated treatments. Liquid conidial applications were less effective. Plants were killed by a preemergence damping-off. Applications made postemergence were significantly less effective. Results of these tests suggest that this fungus has potential as a mycoherbicide for controlling sicklepod, coffee senna, and hemp sesbania. Nomenclature: Cassia obtusifolia L. #3 CASOB; coffee senna, Cassia occidentalis L. # CASOC; hemp sesbania, Sesbania exaltata Rydb. ex A. W. Hill # SEBEX; Fusarium oxysporum Schlet. Additional index words: Biological control, biological herbicide, mycoherbicide.

Nine isolates of Alternaria alternata were obtained from infected tomato (cv. Beefsteak) plants. Each isolate was grown on autoclaved rice medium and corn meal agar medium and evaluated for pathogenesis and phytotoxicity to jimsonweed plants. Only A. alternata SWSL 1 (NRRL 18822) caused lodging on 1-week-old jimsonweed plants when sprayed at a rate of 20 g of fungus-infested rice per 100 mL distilled water. The symptoms began within 24 to 48 h following inoculation, and all plants were dead after 96 h. Treatment of 2-week-old jimsonweed plants in the same manner affected growth only. No symptoms occurred when SWSL 1 spores from corn meal agar were applied to jimsonweed at a rate of 2 × 107 spores/mL, with or without dew. The filtrates of fungus-infested rice of the SWSL 1 isolate were found to contain the following phytotoxins: AAL-toxin (100 μg/g), tenuazonic acid (10 μg/g), and alternariol monomethyl ether (580 μg/g). Crude and cell-free filtrates and AAL-toxin (concentration 200 μg/mL) caused similar damage on excised leaves, characterized by soft rot diffusing from the point of inoculation along the veins, adaxially or abaxially to leaves. Alternariol monomethyl ether (concentration 800 μg/mL) and tenuazonic acid (concentration 420 μg/mL) applied to excised jimsonweed leaves caused no visible damage. In intact plants, symptoms resulting from the crude filtrate, cell-free filtrate, and the AAL-toxin were identical. A dose–response study of AAL-toxin on excised jimsonweed and black nightshade (Solanum nigrum L.) leaves showed effects at concentrations of 1.56 μg/mL and 0.01 μg/mL, respectively. This is the first report of phytotoxicity of AAL-toxin to these two weeds and it may have potential as a weed control agent. Key words: weed, natural products, solid media, fungi.

Eight Fusarium spp. were isolated from greenhouse-grown jimsonweed (Datura stramonium L.) in Mississippi in 1990. Four isolates of Fusarium moniliforme were obtained and when grown on autoclaved rice, produced 115 to 3,200 mg/kg fumonisin B1, (FB1). Other fumonisin-related compounds, such as FB2, FB3 and FB4 were also produced at levels of 240, 210 and 160 mg/kg, respectively. F. semitectum (1 isolates) was negative for production of fumonisin and other phyto-toxins. F. oxysporutn (1 isolate) produced only 3.5 g/kg moniliformin. This is the first report of production of fumonisins by F. moniliforme isolated from weeds such as jimsonweed.

Fumonisin B1(FB1) sprayed on intact jimsonweed plants at 10 to 200 μg ml–1caused chlorosis and necrosis on three- to four-leaf plants and reduced their height and biomass. Excised leaves of jimsonweed were necrotic on both surfaces after treatment with FB1at 10 to 200 μg ml–1. The degree of damage increased with the concentration of FB1. The minimum amount of FB1that damaged excised leaves was 0.05 μg. The symptoms of toxicity on sensitive plants varied with concentration of FB1. Symptoms observed included: chlorosis (creeping cucumber), necrosis (jimsonweed and common sunflower), black leaf lesions (sicklepod), curl of tissues (soybean), stunting, defoliation (hemp sesbania and northern jointvetch), and death (prickly sida, spurred anoda, northern jointvetch, and jimsonweed). Monocots (barley, bermudagrass, corn, johnsongrass, rice, sorghum, and wheat) were not visibly affected by FB1. This is the first evidence of the phytotoxic properties of fumonisin B1against a wide variety of weeds and crop cultivars.

A previously unreported anthracnose disease incited by Colletotrichum truncatum was discovered on hemp sesbania seedlings in Washington County, Mississippi, in 1987. Hemp sesbania inoculated with 2×10 7 spores per milliliter in the greenhouse were killed within 7 days. Soybean cvs. Bragg, Bedford, and Hill developed small, necrotic leaf spots, but no further symptoms occurred after 3 wk. Several cultivars of cotton, rice, and 23 other plant species representing eight plant families were immune to disease, as measured by visual assessment(.)

Alternaria cassiaeJurair and Khan applied as conidia at 1 × 105spores/ml controlled 100% of sicklepod, and 1 × 106spores/ml controlled coffee senna in the greenhouse. In the field, sicklepod control did not differ between one or two fungal applications, but coffee senna control increased following two applications. Although showy crotalaria resistedA. cassiaeinfection more than the other two weeds, total biomass was reduced significantly in both greenhouse and field tests.

An indigenous, host-specific, pathogenic fungus that parasitizes winged waterprimrose [Jussiaea decurrens(Walt.) DC.] is endemic in the rice growing region of Arkansas. The fungus was isolated and identified asColletotrichum gloeosporioides(Penz.) Sacc. f.sp. jussiaeae(CGJ). It is highly specific for parasitism of winged waterprimrose and not parasitic on creeping waterprimrose (J. repensL. var.glabrescensKtze.), rice (Oryza sativaL.), soybeans [Glycine max(L.) Merr.], cotton (Gossypium hirsutumL.), or 4 other crops and 13 other weeds. The fungus was physiologically distinct from C.gloeosporioides(Penz.) Sacc. f. sp.aeschynomene(CGA), an endemic anthracnose pathogen of northern jointvetch[Aeschynomene virginica(L.) B.S.P.], as indicated by cross inoculations of both weeds. Culture in the laboratory and inoculation of winged waterprimrose in greenhouse, growth chamber and field experiments indicated that the pathogen was stable, specific, and virulent in a wide range of environments. The pathogen yielded large quantities of spores in liquid culture. It is suitable for control of winged waterprimrose. Winged waterprimrose and northern jointvetch were controlled in greenhouse and field tests by application of spore mixtures of CGJ and CGA at concentrations of 1 to 2 million spores/ml of each fungus in 94 L/ha of water; the fungi did not damage rice or nontarget crops.