Phoma Macrostoma Research Articles

The effect of fertilizers on the efficacy of the bioherbicide, Phoma macrostoma, to control dandelions in turfgrass

Phoma macrostoma is registered as a bioherbicide in North America to control broadleaved weeds species in turfgrass. A study was conducted to examine the effect of nitrogen, phosphorus, potassium, lime, and commercial fertilizers with or without applications of the bioherbicide on the reduction of dandelion under greenhouse and field conditions. The bioherbicide provided 70–100% reduction of dandelion. The addition of nitrogen with the bioherbicide, in the form of urea (45-0-0), Scotts Turf Builder Pro (32-0-4 plus 2% Fe), and Scotts Lawn Pro (26-0-3, with no iron), significantly reduced dandelion more than in soil that was not amended with fertilizers in the greenhouse and field locations. Bioherbicide efficacy on dandelion was 10–20% better with these fertilizer treatments. Phosphate (0-46-0), potassium sulfate (0-0-42), and lime had either no effect or did not reduce dandelions under greenhouse conditions. This study showed that P. macrostoma retained bioherbicide efficacy on dandelion in conjunction with typical fertility practices and the combination of the bioherbicide with nitrogen fertilizers improved bioherbicide efficacy, especially in low nitrogen soils.

Early Summer Slender Aster Control in Bermudagrass using Bioherbicide Phoma macrostoma

Phoma macrostoma is a fungus being developed as a natural herbicide (bioherbicide) for selective weed control in turfgrass. Previous research with this product is limited to cool-season turfgrass, and information is limited on appropriate application rates or efficacy at higher temperatures and weeds associated with warmseason turf. Field studies were conducted in College Station, TX to evaluate efficacy of the bioherbicidefor slender aster (Aster subulatusvar. ligulatus Shinners) control in common bermudagrass. In 2011, applications of 128 g m-2, split-applied between days 0 and 28 resulted in good control (88%); however, 64 and 32 g m-2 rates failed to provide adequate control. In 2012, single applications of 128 gave excellent control (94%), while the 32 and 64 g m-2 rates gave poor control (54 and 68%, respectively) relative to untreated plots.No injury to common bermudagrass occurred in either study.

Tracing the origins of White Tip disease of Cirsium arvense and its causal agent, Phoma macrostoma

SummaryCirsium arvense (Asteraceae) is known as creeping thistle in its native range in the UK and Canada thistle in its invasive North American range. Recently, the fungus Phoma macrostoma was registered in Canada as a bioherbicide in turfgrass, where it causes severe chlorosis (White Tip disease) and death of C. arvense and other broadleaved weeds. It was hypothesised that the disease originated in the UK on its thistle host and, therefore, that fungal isolates from both countries should be biologically and genetically similar. Twenty‐six strains in the genus Phoma– isolated during surveys in the UK – were compared morphologically with the type culture of P. macrostoma, tested for bioherbicidal activity using the inoculum mat bioassay and genetically screened with bioherbicide‐specific primers. White tip disease was found to be restricted to the eastern and southern counties of England. Phoma macrostoma was isolated consistently from diseased bleached tissues. Bioherbicidal isolates of P. macrostoma occupy a unique clade, which is phylogenetically distinct but morphologically indistinguishable from the type culture. Most isolates from the UK had the same bioherbicidal activity and similar genetic make‐up as strain SRC 94‐44B, the active ingredient in the registered Canadian product. The origin of all bioherbicidal strains found to date has a clear presence in both Canada and the UK, with strong genetic similarities, supporting the view of a common ancestry. Thus, on the evidence presented, the ‘white tip’ clade of P. macrostoma evolved in southern England. Therefore, the bioherbicide based on strain SRC 94‐44B should also be eligible for registration in the UK, based on the pest risk assessment data already available.

Biological and genetic characterisation of Phoma macrostoma isolates with bioherbicidal activity

The fungus Phoma macrostoma Mont. isolate 94-44B was registered as a bioherbicide for control of broadleaved weeds in Canada and the USA in 2011 and 2012, respectively. To obtain the registrations, the fungus had to be characterised both biologically and genetically. The objectives of this study were to demonstrate that bioherbicidal activity was associated with specific genetic markers and to determine whether bioherbicidal activity was a general trait of the species or only selected isolates. A collection of 64 isolates of P. macrostoma was established. A greenhouse bioassay and bioherbicidal-specific primers were used to determine bioherbicidal activity of all isolates. Only isolates originating from Canada thistle demonstrated the ability to reduce dandelion seedlings and display the 853 bp amplicon for the bioherbicidal-specific primer. Bioherbicidal isolates were consistently differentiated from all other isolates with two main genotypic groupings (I and II) arising from internal transcribed spacer (ITS) and amplified fragment length polymorphisms (AFLP) sequence analyses. Using AFLP, two biotypes of bioherbicidal isolates were also differentiated by the presence or absence of an AFLP marker at a single polymorphic locus. The genetic divergence among the bioherbicidal and nonbioherbicidal isolates of P. macrostoma was only 2.21% which was lower than that reported for other related Phoma sp. Other than the bioherbicidal trait, there was no apparent affiliation of the genetics with known varietal types, host or geographic origin. ITS sequence analysis and AFLP fingerprinting may be used as tools to detect bioherbicidal isolates of P. macrostoma.

First Report of a Leaf Spot on Conyza sumatrensis Caused by Phoma macrostoma in China.

Conyza sumatrensis (Asteraceae), an annual or biennial plant, is native to North and South America. It is an invasive, noxious weed that is widespread in southern and southeastern China. It invades farm land and causes great losses to dry land crops, including wheat, corn, and beans. It also reduces biological diversity by crowding out native plants in the infested areas (3,4). During a search for fungal pathogens that could serve as potential biological control agents of C. sumatrensis, a leaf spot disease was observed in 2010 in Chongqing, China. An isolate (SMBC22) of a highly virulent fungus was obtained from diseased leaves. Pathogenicity tests were performed by placing 6-mm-diameter mycelial disks of 7-day-old potato dextrose agar (PDA) cultures of SMBC22 on leaves of 15 healthy greenhouse-grown plants of C. sumatrensis; the same number of control plants was treated with sterile PDA disks. Treated plants were covered with plastic bags for 24 h and maintained in a growth chamber with daily average temperatures of 24 to 26°C, continuous light (3,100 lux), and high relative humidity (>90%). Lesions similar to those observed in the field were first obvious on the SMBC22-inoculated leaves 3 days after inoculation. Symptoms became severe 7 to 9 days after inoculation. Control plants remained healthy. The fungus was reisolated from inoculated and diseased leaves and it was morphologically the same as SMBC22. The pathogenicity test was conducted three times. A survey of 10 southern and southeastern Chinese provinces revealed that the disease was widespread and it attacked leaves and stems of seedlings and mature plants of C. sumatrensis. Lesions on leaves were initially small, circular, and water soaked. The typical lesion was ovoid or fusiform, dark brown, and surrounded by a yellow halo. The spots coalesced to form large lesions and plants were often completely blighted. Fungal colonies of SMBC22 on PDA plates were initially white and turned dark gray. Colonies were circular with smooth edges with obvious rings of pycnidia on the surface. Aerial hyphae were short and dense. Pycnidia, black and immersed or semi-immersed in the medium, were visible after 12 days of incubation. Pycnidia were 72 to 140 μm in diameter. Conidia were produced in the pycnidia and were hyaline, unicellular, ellipsoidal, and 4.4 to 6.1 × 1.6 to 2.2 μm. To confirm identification of the fungus, genomic DNA was extracted from mycelia of a 7-day-old culture on PDA at 25°C (2). The internal transcribed spacer (ITS) gene of rDNA was amplified using primers ITS4/ITS5. The gene sequence was 524 bp long and registered in NCBI GenBank (No. HQ645974). BLAST analysis showed that the current sequence had 99% homology to an isolate of Phoma macrostoma (DQ 404792) from Cirsium arvense (Canada thistle) in Canada and reported to cause chlorotic symptoms on that host plant (1). To our knowledge, this is the first report of P. macrostoma causing disease on C. sumatrensis in China. P. macrostoma, thought of as a biocontrol agent of broadleaf weeds in Canada, has been patented in the United States. The current isolate of P. macrostoma is considered as a potential biocontrol agent of C. sumatrensis.

First Report of a Root and Crown Disease of the Invasive Weed Lepidium draba Caused by Phoma macrostoma.

The exotic rangeland perennial Lepidium draba occurs as a noxious weed in 22 states, mostly in the western United States. Because chemical control measures against this invasive perennial, a member of the Brassicaceae, have not achieved adequate results, biological control is being pursued. While inventories of arthropods that feed on L. draba have been established, little is known of soilborne pathogens for possible use as biological control agents. To address this deficiency, we have surveyed for diseases of L. draba in the United States and Eurasia to identify and test potential biocontrol agents. In intensive surveys for soilborne diseases in a single infestation that is >20 years old in a cattle pasture in south-central Montana, several chlorotic, stunted plants were noted. Roots of chlorotic plants that exhibited elongated fissures from which other soilborne fungi were isolated also had numerous prominent pycnidia embedded in the crown tissue above the lesions. Examination with a dissecting microscope revealed large ostioles made evident by the wide concave inversions in the short necks of the pycnidia. Culture of root tissue on potato dextrose agar resulted in whitish, becoming pale gray colonies, with a dull peach-to-reddish tinge at the margins, with abundant single pycnidia. Conidia in vitro were mainly unicellular, variable shape, subglobose to ellipsoidal, with several guttules averaging 6 × 2.5 μm. These morphological traits are characteristic of Phoma macrostoma, which is regarded as a weak or wound pathogen. The internal transcribed spacer region of rDNA was amplified using primers ITS1 and ITS4 and sequenced. BLAST analysis of the 575-bp fragment showed a 100% homology with the sequence of an isolate of P. macrostoma that has been investigated extensively for commercialization as a biological control agent of various agricultural weeds (1), including wild mustard (GenBank No. DQ474091). The nucleotide sequence has been assigned GenBank No. HM755951. Pathogenicity tests consisted of making four 1.4-mm-diameter holes in five NaOCl (0.1%)-sterilized root sections of L. draba and pipetting ~50 to 100 μl of a 106 CFU/ml conidial suspension into the incisions, incubating the inoculated roots at 20 to 25°C overnight and planting the root sections, one per pot, in an artificial greenhouse potting mix and placing the pots in the greenhouse at 20 to 25°C. Controls were five root sections that were treated similarly except that sterile water was injected. The experiment was repeated. After 10 days, shoots that grew from inoculated roots were chlorotic and shorter than those produced from control roots. P. macrostoma was isolated from tissue of inoculated roots that became blackened distal to the inoculation points. To examine the host range of P. macrostoma on other brassica species, crowns of 2-week-old seedlings of radish, broccoli, cauliflower, broccoli raab, turnip, kohlrabi, cabbage, Chinese cabbage, mustard greens, and canola were injected with 0.5 ml of a 106 CFU/ml conidial suspension. Plants were grown in the greenhouse at 20 to 25°C for 4 weeks after inoculation and examined for symptoms. The experiment was repeated twice. Blackened root tissue with slight chlorosis occurred only on roots of radish and crowns of broccoli, from which P. macrostoma was reisolated. To our knowledge, this the first report of a disease of L. draba caused by P. macrostoma. Reference: (1) K. L. Bailey et al. U.S. Patent Application Serial No. 60/294,475, Filed May 20, 2001.

Intracellular Biosynthesis of Gold Nanoparticles by Fungus Phoma macrostoma

Nanomaterials are at the leading edge of the rapidly developing field of nanotechnology. The authors investigated biosynthesis of gold nanoparticles using the fungus Phoma macrostoma. Intracellular biosynthesis of gold nanoparticles was obtained by incubating HAuCl4 solution with the fungal biomass for 48 h. The gold nanoparticles exhibited maximum absorbance at 550 nm in UV-vis spectroscopy. The XRD spectrum showed Bragg reflections corresponding to the gold nanoparticles. Transmission electron microscopy illustrated the production of intracellular gold nanoparticles with the size range of 100–200 nm in spherical, triangle, and rod shapes.

Determining the infection process of Phoma macrostoma that leads to bioherbicidal activity on broadleaved weeds

Isolates of the fungus Phoma macrostoma cause intense photobleaching and mortality of Canada thistle (Cirsium arvense), dandelion (Taraxacum officinale) and other broadleaved weeds when applied to the soil. The symptoms are caused by the production of macrocidins which have been extracted from cultured mycelium and the growth medium broth. The objective of this study was to determine the pathway of infection that leads to plant damage resulting in bioherbicidal activity. This was accomplished by first determining which infective unit (i.e., conidia and/or mycelium) resulted in plant damage when applied to a host. Then the infection process was microscopically observed from infested granules placed in the soil through the various stages of colonization and penetration in a resistant and a susceptible host. Conidia were ineffective as infective units because there was no plant damage when target weeds were inoculated using either a foliar spray of a conidial suspension or granules containing conidia placed in the soil. Only mycelium of the fungus applied either pre-emergently to soil ahead of weed seed emergence or post-emergently to soil containing established weeds resulted in significant plant damage. Microscopic observations showed that P. macrostoma 94-44B mycelium germinated from formulated granules in soil, colonizing roots of dandelion (susceptible) and barley (resistant) within 7days of application. The fungus entered the hosts at sites proximal to root hairs where wounding of the cells was most likely, and growing intercellularly towards the root core. In dandelion, the mycelium proliferated around the vascular trachea disrupting the competence of neighboring cells. In barley, proliferation was less obvious being restricted to the outer layers and there was no disruption of the internal cell structure. P. macrostoma boasts potential as a bioherbicide to control susceptible broadleaved weeds but not harm resistant nontarget hosts.

The effects of Phoma macrostoma on nontarget plant and target weed species

Phoma macrostoma 94-44B was evaluated against 94 plant species in 34 botanical families, of economically important agricultural, horticultural and ornamental species, as well as target and nontarget weeds. Fifty-seven species from 28 families were found to be resistant to P. macrostoma, while 38 species from 12 families, six of which also contained resistant species, were found to be susceptible. Those families comprising both susceptible and resistant species included the Asteraceae, Brassicaceae, Fabaceae, Lamiaceae, Plantaginaceae and Rosaceae with the foremost three containing the largest numbers of susceptible species. P. macrostoma was pathogenic to many dicotyledonous plant species, but nonpathogenic to monocots. Commercial applications for weed management in turfgrass, agriculture, horticulture and forestry seem probable, while domestically management of weeds in lawns, transplanted ornamental and annual flowering species may provide alternative markets.

The Biotransformation of Aromatic Amino Acids by Phoma macrostoma

A search for natural products produced in fermentation cultures of a strain of Phoma macrostoma led to the identification of tyrosol as the major metabolite produced by this organism. The addition of the amino acid tyrosine to growing fermentation cultures of P. macrostoma resulted in an increase in the production of tyrosol. It was subsequently determined that this strain of P. macrostoma was also capable of the biotransformation of other amino acids into similar alcohols.

Annual Meeting, Winnipeg, Manitoba, 2009

Annual Meeting, Winnipeg, Manitoba, 2009

Caracterización morfológica, patogénica y molecular de Phoma spp. aislados del suelo de predios de cebolla en Puerto Rico

Se examinaron 13 aislados de Phoma spp. recolectados durante un catastro de hongos de suelo llevado a cabo en predios de cebolla en Santa Isabel, Puerto Rico, a base de sus características morfológicas, patogénicas y moleculares. Doce aislados fueron identificados como P. putaminum y un aislado como P. macrostoma var. incolorata atípico (sección Phyllostictoides). Este es el primer informe de P. putaminum y P. macrostoma var. incolorata para Puerto Rico y el Caribe. In vitro, P. putaminum fue patogénico a los cvs. de cebolla Mercedes y Excalibur, resultando en necrosis de los bulbos y raíces jóvenes siete días después de la inoculación. La incidencia de la enfermedad causada por P. putaminum fue mayor en el cultivar Mercedes (75 a 100%) que en P. macrostoma var. incolorata (0 a 25%). No se observaron síntomas en el cultivar Excalibur inoculado con P. macrostoma var. incolorata o en las plantas control. Ni las inoculaciones in vitro de bulbos comerciales de cebolla, ni de raíces en condiciones de campo reprodujeron síntomas, demostrando así que P. putaminum y P. macrostoma var. incolorata son patógenos débiles. El tamaño de la región espadadora interna (ITS) del gen del ADN ribosómico fluctuó entre 458 a 610 bp para P. putaminum y 456 bp para el aislado de P. macrostoma. El análisis de la región ITS del rADN mediante PCR-RFLP demostró que la enzima de restricción, Hindlll, entre otras enzimas de restricción evaluadas (Alul, EcoRI, Clal y Seal) diferenció entre P. putaminum y P. macrostoma var. incolorata.

Effect of autumn application of urea on saprotrophic fungi in off-season leaf litter of sour cherry and evaluation of fungal isolates to reduce primary inoculum of Blumeriella jaapii

The effect of autumn application of urea on the activity and composition of saprotrophic fungi associated with sour cherry (Prunus cerasus) leaf litter infected with the leaf spot pathogen, Blumeriella jaapii, was studied under orchard conditions from the time of leaf fall to the release of ascospores, the following spring. The ability of treatment of infected leaves post leaf fall with urea or with inoculum of selected fungal strains to reduce primary inoculum (ascospores and winter conidia) of B. jaapii in spring was evaluated. Fungal activity was measured enzymatically by quantifying β-N-acetylgly-cosaminidase and fungal composition and frequency were evaluated following isolation at low temperature of mycelia embedded in leaf particles. Activity of the general fungal flora increased in both the urea and water treatments throughout the experimental period and a significantly higher level of activity was detected in urea-treated leaves up to 79 days after treatment. Most of the 2,146 fungal isolates recovered from the leaf litter during November-May could be placed in the following six groups: Phoma macrostoma (52.7%), other Pho-ma spp. (12.3%), Cladosporium spp. (13.8%), Alternaria and Ulocladium spp. (5.4%), Epicoccum purpurascens (2.9%) and Fusarium spp. (1.6%). These groups were isolated from the leaf litter throughout the experimental period and the effect of urea on fungal composition in the litter was very limited. Of these groups only the frequency of recovery of E. purpurascens was higher from urea than from water-treated leaves and this significant difference was maintained throughout the 115 days of the experimental period. Phoma macrostoma var. macrostoma, Cladosporium sp., Ulocladium chatarum, Epicoccum purpurascens and Fusarium lateritium var. lateritium were evaluated and compared with urea to reduce primary inoculum of B. jaapii. Urea reduced primary inoculum of B. jaapii in the spring by 77% and of the fungal strains, especially Cladosporium strain MB167 was found to be equally effective.

Annual Meeting, Québec, Quebec, 2006, The Canadian Phytopathological Society / Réunion annuelle, Québec, Québec, 2006, La Société canadienne de phytopathologie

Annual Meeting, Québec, Quebec, 2006, The Canadian Phytopathological Society / Réunion annuelle, Québec, Québec, 2006, La Société canadienne de phytopathologie

Molecular and genetic analyses of geographic variation in isolates of Phoma macrostoma used for biological weed control

Molecular and genetic approaches were used to evaluate the genetic relatedness among isolates of the fungus Phoma macrostoma Montagne originating from Canada and Europe and to other species in the genus Phoma. Distinct differences were observed in genetic variation among nine species of the genus Phoma. Randomly amplified polymorphic DNA (RAPD) revealed the presence of intraspecific genetic variation among the isolates of P. macrostoma, with the isolates being used for biological weed control being distributed in a distinct phylogenetic cluster. Additional variation within the biocontrol isolate cluster in P. macrostoma was revealed by pulsed field gel electrophoresis (PFGE), which showed that bio-control isolates generated two different chromosomal profiles, however the profiles did not relate to their Canadian ecozone origin. Mating studies showed that biocontrol isolates of P. macrostoma from Canada did not produce sexual reproductive structures and were incapable of crossing. These studies also confirmed that no obvious differentiation exists among the bio-control isolates of P. macrostoma from Canadian Eco-zones 3 and 4.

Molecular and genetic analyses of geographic variation in isolates of Phoma macrostoma used for biological weed control

Molecular and genetic approaches were used to evaluate the genetic relatedness among isolates of the fungus Phoma macrostoma Montagne originating from Canada and Europe and to other species in the genus Phoma. Distinct differences were observed in genetic variation among nine species of the genus Phoma. Randomly amplified polymorphic DNA (RAPD) revealed the presence of intraspecific genetic variation among the isolates of P. macrostoma, with the isolates being used for biological weed control being distributed in a distinct phylogenetic cluster. Additional variation within the biocontrol isolate cluster in P. macrostoma was revealed by pulsed field gel electrophoresis (PFGE), which showed that biocontrol isolates generated two different chromosomal profiles, however the profiles did not relate to their Canadian ecozone origin. Mating studies showed that biocontrol isolates of P. macrostoma from Canada did not produce sexual reproductive structures and were incapable of crossing. These studies also confirmed that no obvious differentiation exists among the biocontrol isolates of P. macrostoma from Canadian Ecozones 3 and 4.

Saskatchewan Regional Meeting, 2004

Biological control of apple scab using Microsphaeropsis ochracea: the impact of water volume, spore concentration, and formulation. K.L. Bailey, O. Carisse, M. Leggett, G. Holloway, F. Leggett, T.M. Wolf, A. Shivpuri, J. Derby, B. Caldwell, and H.J. Geissler. Saskatoon Research Centre, Agriculture and Agri-Food Canada (AAFC), 107 Science Place, Saskatoon, SK S7N 0X2, Canada; (O.C.) Horticultural Research and Development Centre, AAFC, 430 Gouin Boulevard, Saint-Jean-sur-Richelieu, QC J3B 3E6, Canada; (F.L.) Lethbridge Research Centre, AAFC, P.O. Box 3000, Lethbridge, AB T1J 4B1, Canada; (M.L., G.H.) Philom Bios, 318–111 Research Drive, Saskatoon, SK S7N 3R2, Canada; and (A.S.) Rajasthan Agricultural University, Durgapura, Jaipur 302018, India. Screening of Brassica napus and Phaseolus vulgaris for physiological resistance to Sclerotinia sclerotiorum. L. Buchwaldt, D. Hegedus, R. Li, and R. Rimmer. Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada. Brassinin-detoxifying enzymes from the pathogenic fungus Leptosphaeria maculans isolates Laird-2 and Mayfair-2. R.S. Gadagi, M. Jha, and M.S.C. Pedras. Department of Chemistry, 110 Science Place, University of Saskatchewan, Saskatoon, SK S7N 5C9, Canada. Effect of camalexin and spirobrassinin on the rate of detoxification of the phytoalexin brassinin by Leptosphaeria maculans (Phoma lingam). M. Jha and M.S.C. Pedras. Department of Chemistry, 110 Science Place, University of Saskatchewan, Saskatoon, SK S7N 5C9, Canada. Mapping the blackleg resistance gene LepR3 using Arabidopsis–Brassica collinearity. N. Larkan, M. Nelson, F. Yu, C. Hammond, I. Parkin, W. Cowling, D. Lydiate, and R. Rimmer. School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia; and (F.Y., C.H., I.P., D.L., R.R.) Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada. Brassinin oxidase — a phytoalexin-detoxifying enzyme from the phytopathogenic fungus Leptosphaeria maculans. O. Okeola, M. Jha, and M.S.C. Pedras. Department of Chemistry, 110 Science Place, University of Saskatchewan, Saskatoon, SK S7N 5C9, Canada. Preliminary population structure analysis of Plectosporium alismatis — a potential biocontrol agent for Alismataceae in Australian rice crops. W.M. Pitt, G.J. Ash, and E.J. Cother. Farrer Centre, School of Agriculture, Charles Sturt University, P.O. Box 588, Wagga Wagga, NSW 2678, Australia; and (E.J.C.) New South Wales Agriculture, Agricultural Research Institute, Forest Road, Orange, NSW 2800, Australia; (W.M.P.) present address: Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada. Phoma macrostoma — ITS sequencing provides confirmation of a unique genotype. W.M. Pitt, K.L. Bailey, Y.B. Fu, and G.W. Peterson. Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada. Putative transformation of the Alismataceae pathogen Plectosporium alismatis. W.M. Pitt, J.L. Taylor, G.J. Ash, and E.J. Cother. Farrer Centre, School of Agriculture, Charles Sturt University, P.O. Box 588, Wagga Wagga, NSW 2678, Australia; (J.L.T.) National Research Council of Canada, Plant Biotechnology Institute, 110 Gymnasium Place, Saskatoon, SK S7N 0W9, Canada; and (E.J.C.) New South Wales Agriculture, Agricultural Research Institute, Forest Road, Orange, NSW 2800, Australia; (W.M.P.) present address: Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada. Chemical investigation of phytoalexins from Brassica spp. M.G. Sarwar, M. Suchy, and M.S.C. Pedras. Department of Chemistry, 110 Science Place, University of Saskatchewan, Saskatoon, SK S7N 5C9, Canada.

Plant colonization and environmental fate of the biocontrol fungus Phoma macrostoma

Plant colonization and environmental fate of the biocontrol fungus Phoma macrostoma

Plant colonization and environmental fate of the biocontrol fungus Phoma macrostoma

Several isolates of the fungus Phoma macrostoma demonstrated bioherbicidal activity against dandelion seedlings when applied to soil. Weed control ranged from 36 to 100% depending on the isolates and the doses applied. Using microbiological and molecular genetic techniques, the ability of these isolates to colonize target, and nontarget plants and to disperse and persist in soil were determined. PCR primers highly specific to the biocontrol isolates of P. macrostoma, were used to detect the isolates at rates of application between 4 and 1000 g/m2. Based on the results from representative isolates tested, it was concluded that P. macrostoma colonized root tissues of both resistant and susceptible crop species and a susceptible weed species grown in treated soil, and the frequency of fungal isolation declined with time. It was occasionally detected on untreated plant tissues, which may have resulted from either natural occurrences on seed, or contamination of soil. The biocontrol fungus appeared to have limited mobility in the soil since it was not often detected away from the area where it was placed. It persisted in the soil at detectable levels for up to 4 months, but then its presence declined with time. One year post application, P. macrostoma was either not present or significantly reduced in both soil and plant samples depending on the year of sampling. The results suggested that the isolates of P. macrostoma used for biological weed control would have minimal environmental impact due to its ubiquitous nature, limited mobility, and weak persistence over seasons.

The macrocidins: novel cyclic tetramic acids with herbicidal activity produced by Phoma macrostoma.

Field isolates of Phoma macrostoma were obtained from diseased Canada thistle growing in several geographically diverse regions. Bleaching and chlorotic symptoms were present on the infected plants. The isolates grown in liquid culture were found to produce phytotoxic metabolites which also caused bleaching when applied foliarly to several broadleaf species. Bioassay-directed isolation led to the discovery of macrocidins A and B, the first representatives of a new family of cyclic tetramic acids. This new chemotype may offer significant potential as a template for herbicide design.