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Jansen R.,Tshwane University of Technology | Makaka L.,Tshwane University of Technology | Little I.T.,University of Cape Town | Dippenaar-Schoeman A.,Plant Protection Research Institute PPRI | Dippenaar-Schoeman A.,University of Pretoria
Insect Conservation and Diversity | Year: 2013

Frequent and extensive burning practices coupled with intensive grazing management are known to impact negatively on the vegetation diversity of grassland ecosystems. Few studies have investigated the impacts on spider diversity and community structure as a result of these management practices, and no studies have been conducted in high mountain grasslands on how these spider assemblages are influenced by this form of management. Here, we present the results of a study conducted in the Mpumalanga grasslands on the eastern escarpment of South Africa. Ground-dwelling spiders were sampled in the summer season from 180 pit-fall traps in five study sites that varied from either being burnt annually and grazed heavily, burnt biennially and conservatively grazed, to communal land with no set management practice. Variations between sites were assessed and based on spider species composition and assemblage structure. A total of 1145 individuals were collected representing 86 species from 60 genera and 43 families. Our results show that a majority of genera in these grasslands were represented by very few individuals, where a total of 37 species were represented by singletons and 17 species that were doubletons. The most abundant families were the Lycosidae (64.3%), Gnaphosidae (9.0%), Zodariidae (5.3%), Linyphiidae (4.7%) and Salticidae (3.1%). Grazing intensity and fire frequency had no measurable effect on ground-dwelling spider abundance diversity or assemblage structure. Only when rare or single species occurrence was included, was there some form of association with sites. This study has provided for the first preliminary inventory of ground-dwelling spiders for this habitat. © 2013 The Royal Entomological Society. Source

Goodall J.,University of Witwatersrand | Goodall J.,Plant Protection Research Institute PPRI | Witkowski E.T.F.,University of Witwatersrand | McConnachie A.J.,Plant Protection Research Institute PPRI | Keen C.,PO Box 245
Biological Invasions | Year: 2012

The alien forb Campuloclinium macrocephalum (Less.) DC. (Asteraceae, pompom weed) invades disturbed rangelands in South Africa. After >40 years of naturalisation, infestations around Pretoria were severely damaged in 2006 by the biotrophic rust Puccinia eupatorii Dietel (Pucciniaceae). The disease spread rapidly and has now established at most pompom weed infestations in the country. This study reports on the efficacy of the pathogen as a biocontrol agent of pompom weed, its effect on the retention of the weed's realised niche and tolerance to the disease. Eighty rangeland infestations originally assessed over two years in 2003 and 2004 were re-surveyed in 2009. Data from untreated plots at two pompom weed experimental sites where the rust was first detected were also used. Puccinia eupatorii induced premature senescence in late summer and stimulated the production of compensatory growth in autumn. Plants without disease symptoms senesced in late autumn without compensatory growth and remained dormant throughout winter. Pompom weed density did not change significantly over time in both the rangeland study and untreated plots. Disease incidence in rangelands in 2009 was most severe in dense infestations, with sparse infestations having the highest incidence of natural senescence and fewer pustules. The rust did not reduce the realised niche; infestations in grasslands, savanna and wetlands persisted despite significant damage by the disease. Persistence, despite high annual stem mortality, suggests that pompom weed remains adapted to the fungus after prolonged separation from the disease. This study supports earlier findings that disturbance remains key to pompom weed invasion even under biological control. The rust may enhance the biological control of pompom weed with augmentation of additional insect agents, but is unlikely to inflict a significant reduction in the weed's population on its own. This may be an important consideration for the biological control of weeds involving biotrophic fungi. © 2012 Springer Science+Business Media B.V. Source

Ta H.-A.,Plant Protection Research Institute PPRI | Nguyen D.-P.,Plant Protection Research Institute PPRI | Causse S.,IRD Montpellier | Nguyen T.-D.,IRD Montpellier | And 2 more authors.
Virus Genes | Year: 2013

Rice grassy stunt virus (RGSV, Tenuivirus) recently emerged on rice in Vietnam, causing high yield losses during 2006-2009. The genetic diversity of RGSV is poorly documented. In this study, the two genes encoded by each ambisense segment RNA3 and RNA5 of RGSV isolates from six provinces of South Vietnam were sequenced. P3 and Pc3 (RNA3) have unknown function, P5 (RNA5) encodes the putative silencing suppressor, and Pc5 (RNA5) encodes the nucleocapsid protein (N). The sequences of 17 Vietnamese isolates were compared with reference isolates from North and South Philippines. The average nucleotide diversity among the isolates was low. We confirmed a higher variability of RNA3 than RNA5 and Pc3 than P3. No relationships between the genetic diversity and the geographic distribution of RGSV isolates could be ascertained, likely because of the long-distance migration of the insect vector. This data will contribute to a better understanding on the RGSV epidemiology in South Vietnam, a prerequisite for further management of the disease and rice breeding for resistance. © 2012 Springer Science+Business Media New York. Source

Goodall J.M.,University of Witwatersrand | Goodall J.M.,Plant Protection Research Institute PPRI | Witkowski E.T.F.,University of Witwatersrand
Weed Research | Year: 2014

We report on the performance of the registered herbicides picloram and metsulfuron-methyl on the control of Campuloclinium macrocephalum (pompom weed) in grasslands. Herbicide trials in hydric and xeric grasslands were treated for three consecutive years in either summer (February) or autumn (April) and monitored for an additional 3 years after spraying ceased. Uncontrolled factors such as a host-specific rust, fire and drought were observed from the second year of the study. Metsulfuron-methyl and picloram did not differ in efficacy according to the timing of applications, but average mortality of marked plants was <80% expected of registered herbicides. Populations of C. macrocephalum in plots were reduced proportionately to the percentage mortality of marked plants. Picloram and metsulfuron-methyl applied at 252 g a.i. ha-1 and 45 g a.i. ha-1, respectively, were not detectable by gas chromatography in the upper 25 cm of the soil profile during any of the sampling intervals from 0 to 56 days after treatment. Three annual applications of registered herbicide did not reduce C. macrocephalum successfully, and it is estimated that between five (summer) to seven (autumn) annual treatments are required to reduce weed density to <1 plant per plot (25 m2). Future research should focus on rust-herbicide interactions, the role of fire in seedbank management and fire as a treatment that could be integrated with chemical control. © 2014 European Weed Research Society. Source

Tam L.T.T.,Plant Protection Research Institute PPRI | Thanh H.M.,Plant Protection Research Institute PPRI | Tuyen N.H.,Plant Protection Research Institute PPRI | Dung P.N.,Plant Protection Research Institute PPRI | And 2 more authors.
Plant Disease | Year: 2016

In a survey of powdery mildews in Viet Nam in 2013, Erysiphales specimens were found on bellyache bush (Jatropha gossypifolia). The plants were grown as an ornamental houseplant or as a hedge in Ha Noi. The incidence of disease was approximately 90 to 100% of leaves at multiple locations in Ha Noi. Within three weeks of first detection of the disease, almost all surfaces of leaves were covered by the white fungal growth. The disease became severe during August 2014, reducing the esthetic value of infected plants, with most being unmarketable. A representative specimen was deposited in the PPRI Herbarium (Accession No. PPRI-PM057). Conidiophores were 100 to 137.5 μm long. Foot-cells of conidiophores were 75 to 95 × 10 to 12.5 μm long. Conidia produced singly were variable in shape, 35 to 40 × 20 to 22.5 μm with a length/width ratio of 1.8 to 1.9, with distinct fibrosin bodies. Conidia germinated with brevitubus subtype of Fibroidium type germ tubes. No chasmothecia were found. The morphological characteristics were consistent with descriptions of Podosphaera xanthii (Castagne) U. Braun & Shishkoff, 2000 (Braun and Cook, 2012). To confirm the identity of the causal fungus, the complete ITS region of rDNA from isolate PPRI- PM057 was amplified by primer pairs ITS1/P3 (White et al. 1990; Kusaba and Tsuge 1995) and directly sequenced. The resulting sequence was deposited in GenBank (Accession No. KM260741). A BLAST search of this sequence showed 100% identity with several P. xanthii isolates from various families of host plants (e.g., AB046985 and AB040339). Pathogenicity was confirmed by gently pressing diseased leaves of bellyache bush onto young leaves of three one-year-old seedlings of J. gossypifolia in a glass house maintained at 27 to 28°C. Three noninoculated seedlings were used as controls. Inoculated leaves developed symptoms after 10 days, whereas the control plants remained symptomless. The fungus present on the inoculated leaves was morphologically identical to that observed on the original diseased leaves, with the same ITS sequence, fulfilling Koch’s postulates. According to Braun and Cook (2012), there has only been one report of a powdery mildew on a Jatropha sp., which was Erysiphe jatrophae in South Africa. To our knowledge, this is the first report of powdery mildew caused by P. xanthii on bellyache bush in Viet Nam. This disease seems to be a serious threat to the commercial production of bellyache bush plants. Moreover, the disease on this host could be a potential source in inoculum for cucurbits in Viet Nam. © The American Phytopathological Society. Source

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