Showing papers by "Michael J. Wingfield published in 1997"

Population Structure of Phytophthora cinnamomi in South Africa.

Abstract: Linde, C., Drenth, A., Kemp, G. H. J., Wingfield, M. J., and von Broembsen, S. L. 1997. Population structure of Phytophthora cinnamomi in South Africa. Phytopathology 87:822-827. Phytophthora cinnamomi isolates collected from 1977 to 1986 and 1991 to 1993 in two regions in South Africa were analyzed using isozymes. A total of 135 isolates was analyzed for 14 enzymes representing 20 putative loci, of which four were polymorphic. This led to the identification of nine different multilocus isozyme genotypes. Both mating types of P. cinnamomi occurred commonly in the Cape region, whereas, predominantly, the A2 mating type occurred in the Mpumalanga region of South Africa. A2 mating type isolates could be resolved into seven multilocus isozyme genotypes, compared with only two multilocus isozyme genotypes for the A1 mating type isolates. Low levels of gene (0.115) and genotypic (2.4%) diversity and a low number of alleles per locus (1.43) were observed for the South African P. cinnamomi population. The genetic distance between the Cape and Mpumalanga P. cinnamomi populations was relatively low (Dm = 0.165), and no specific pattern in regional distribution of multilocus isozyme genotypes could be observed. The genetic distance between the “old” (isolated between 1977 and 1986) and “new” (isolated between 1991 and 1993) P. cinnamomi populations from the Cape was low (Dm = 0.164), indicating a stable population over time. Three of the nine multilocus isozyme genotypes were specific to the “old” population, and only one mu ltilocus isozyme genotype was specific to the “new” population. Significant differences in allele frequencies, a high genetic distance ( Dm = 0.581) between the Cape A1 and A2 mating type isolates, significant deviations from HardyWeinberg equilibrium, a low overall level of heteroz ygosity, and a high fixation index (0.71) all indicate that sexual reproduction occurs rarely, if at all, in the South African P. cinnamomi population.

Two species in the Ceratocystis coerulescens complex from conifers in western North America

Abstract: Two species of Ceratocystis are described from western North America. Ceratocystis rufipenni Wingfield, Harrington, & Solheim is associated with the North American spruce bark beetle Dendroctonus rufipennis infesting both Engelmann spruce (Picea engelmannii Parry) and white spruce (Picea glauca (Moench) Voss) in British Columbia. This fungus is a primary component of the bark beetle mycota and has a relatively high degree of virulence to Engelmann spruce. Ceratocystis douglasii (Davidson) Wingfield & Harrington was previously described as Endoconidiophora coerulescens f. douglasii. It is common on Douglas-fir lumber in western North America where it causes blue stain. Both fungi grow optimally at low temperatures and produce perithecia only after extended incubation under refrigeration. Ceratocystis rufipenni produces conidiophores mostly in association with perithecia, whereas conidia and conidiophores of C. douglasii are produced abundantly on wood and agar. Key words: Ceratocystis, Chalara, Dendroctonu...

Genotypic diversity in a South African population of the pitch canker fungus Fusarium subglutinans f.sp. pini

Abstract: The genotypic diversity in a South African population of Fusarium subglutinans f.sp. pini (F.s. pini) was determined, based on the number of vegetative compatibility groups (VCGs). Isolates of F.s. pini from South Africa (69), California (five) and Florida (19) were included in the study. The nit1 (or nit3) and NitM mutants were selected as chlorate resistant sectors and paired on minimal medium. The South African isolates of F.s. pini were assigned to 23 different VCGs. No heterokaryons formed between isolates from South Africa, California and Florida. The high degree of genotypic diversity in the South African population of F.s. pini is probably due to some level of sexual reproduction in the population.

A systemic parvo-like virus in the freshwater crayfish Cherax destructor

Abstract: Systemic Cowdry Type A inclusions (CAs) were observed in a moribund Cherax destructor collected at an aquaculture farm in South Australia. Inclusions were most common in the gills and were associated with multifocal necrosis of the main gill axis and lamellae. The hepatopancreas was necrotic; however, only one CA was observed in the interstitial tissues. CAs were associated with necrosis in the abdominal and gut musculature. CAs were also observed in the spongy connective tissues and the epicardium. Empty capsids (17.5 +/- 0.5 nm) and microfilaments were most commonly observed within these inclusions by transmission electron microscopy. Complete icosahedral viral particles (20.8 +/- 1.2 nm) were difficult to distinguish within the viroplasm, but were visualised better in aggregates between the viroplasm and the inner nuclear membrane. The nucleolus was closely associated with the developing viroplasm, and was hypertrophied and segregated into its fibrillar and granular components. The virus was named Cherax destructor systemic parvo-like virus (CdSPV) on the basis of its histopathology, cytopathology and morphology. CdSPV is the first systemic virus described in a freshwater crayfish.

New species of calonectria and cylindrocladium isolated from soil in the tropics

Abstract: Several Calonectria (Ca.) and Cylindroclad- ium (Cy.) species were recovered from alfalfa-baited soil samples gathered in Colombia and Venezuela. Perithecia of Calonectria naviculata sp. nov. formed in culture when Venezuelan strains of Cy. navicula- tum were crossed with ex-type Brazilian strains. Ca- lonectria gracilipes sp. nov. (anam. Cy. gracilioideum sp. nov.), a homothallic species, was isolated from Co- lombian soils. Cylindrocladium graciloideum, Cy. grac- ile, Cy. pteridis and Cy. pseudogracile form a complex of morphologically similar species characterized by clavate vesicles and primarily 1-septate conidia. Each species could, however, be distinguished using RFLP banding patterns. A key to Calonectria spp. having Cylindrocladium anamorphs with 1-septate conidia is also presented.

The Symptoms and Cause of Guava Wilt in South Africa

Abstract: Wilt of guava (Psidium guajava), a serious disease occurring in most guava producing areas of the Northern and Mpumalanga provinces of South Africa, was shown to be induced by a fungus tentatively identified as Penicillium vermoesenii. This fungus is the cause of a blight of ornamental palms in the United States and Belgium and its occurrence on guava is enigmatic. Pathogenicity tests were conducted in the glasshouse and under field conditions. Symptoms on trees include wilting, chlorosis and defoliation.

First report of Sphaeropsis canker on cypress in South Africa

Abstract: Summary In this study a Sphaeropsis sp. is recorded as causing cankers on cypress in South Africa. These cankers are either found alone or on trees which are infected with the well-known cypress canker pathogen, Seiridium unicorne. When the two fungi occurred together, lesions could not be distinguished from each other, although the greater number of lesions were caused by the Sphaeropsis sp. The fungus appears to be identical to that described as Sphaeropsis sapinea f.sp. cupressi, in Israel, which is a fungus very different from the pine pathogen, Sphaeropsis sapinea. Pathogenicity tests showed that the Sphaeropsis sp. is significantly more pathogenic to Cupressus lusitanica than to Pinus roxburgii and Pinus elliottii. S. sapinea was pathogenic only to the Pinus spp. tested, and not to C. lusitanica. In contrast, the cypress pathogen Seiridium unicorne, was pathogenic to C. lusitanica and also to the two Pinus spp. tested.

A new species of ophiostoma from north america, similar to ophiostoma penicillatum

Abstract: Ophiostomatoid fungi that resemble Ophiostoma penicillatum were isolated from insect-infested spruce (Picea sp.) in Japan as well as Larix decidua Mill. (European larch) in North America. Isolates were characterized based on morphology and could be separated into two distinct groups. Those from spruce in Japan represent O. penicillatum, and are characterized by allantoid, slightly curved conidia. The North American isolates from Larix decidua are of a previously undescribed species, characterized by long, narrow conidia. The latter fungus is described as Ophiostoma americanum with an anamorph, Leptographium americanum. Key words: Ophiostoma penicillatum, Ips typographus, Ophiostoma americanum, Dendroctonus simplex, Larix decidua.

A new Ophiostoma species with a Graphium anamorph from Larix laricina in eastern North America

Abstract: The ophiostomatoid fungi are an economically important group that include various destructive plant pathogens. Knowledge regarding the occurrence of these fungi on larch (Larix spp.) and th...