There are two recognized forms of the disease net blotch of barley: the net form caused by Pyrenophora teres f . teres (PTT) and the spot form caused by P. teres f . maculata (PTM). In this study, amplified fragment length polymorphism analysis was used to investigate the genetic diversity and population structure of 60 PTT and 64 PTM isolates collected across Australia (66 isolates) and in the south‐western Cape of South Africa (58 isolates). For comparison, P. tritici‐repentis , Exserohilum rostratum and Bipolaris sorokiniana samples were also included in the analyses. Both distance‐ and model‐based cluster analyses separated the PTT and PTM isolates into two strongly divergent genetic groups. Significant variation was observed both among the South African and Australian populations of PTT and PTM and among sampling locations for the PTT samples. Results suggest that sexual reproduction between the two forms is unlikely and that reproduction within the PTT and PTM groups occurs mainly asexually.
The commercial cultivation of spineless cactus (Opuntia ficus-indica (L.) Miller) for its fruit is a relatively recent undertaking in South Africa but has been shown to possess huge export potential. To date, only one fungal pathogen, Didymosphaeria opulenta (De Not.) Sacc., has been officially reported on the genus Opuntia in South Africa, but the report is from O. stricta Haw. and not O. ficus-indica (1). The need for research on diseases of O. ficus-indica in South Africa has recently become important since local growers are increasingly reporting disease-related yield losses. Surveys conducted over a period of 3 years indicated that stems or cladodes are particularly prone to various forms of tissue necrosis, caused primarily by three fungi, which can ultimately lead to death of entire cladodes. Alternaria tenuissima was isolated from a dry superficial necrosis of the cuticle and underlying tissue as much as 3 mm deep. Symptoms include small chlorotic spots on the cuticle, which coalesce to form raised gray scabs. Fusarium sporotrichoides was isolated more commonly from dry necrotic lesions that were darker, larger, and less superficial, sometimes extending through the tissue to the opposite side of the cladode. Lasiodiplodia theobromae (teleomorph Botryosphaeria rhodina) was isolated from roundish black cankers (15 to 50 mm diameter) on cladodes and characterized by black gum exudation from the perimeter of the canker. Pycnidia were often evident on the surface of the canker. The fulfillment of Koch's postulates demonstrated that an isolate of each respective species was very aggressive in colonizing cladodes following artificial inoculations in the glasshouse. Mean lesion diameters measuring 15, 27, and 44 mm for A. tenuissima, F. sporotrichoides, and L. theobromae, respectively, were recorded 14 days after inserting wooden toothpick tips that had been colonized by the three pathogens into each of five cladodes of 18-month-old potted plants of O. ficus-indica (cv. Morado). Alternaria sp. and B. rhodina have been reported on Opuntia sp. in the United States (2), but no records of the above three fungi occurring on O. ficus-indica were found. References: (1) P. W. Crous et al. Phytopathogenic Fungi from South Africa. University of Stellenbosch, Department of Plant Pathology Press, Stellenbosch, South Africa, 2000. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989.
A severe outbreak of a foliar disease occurred on ornamental sunflower (Helianthus annuus L. cv. Tyao) cultivated under plastic protection near Potchefstroom in the North West Province during February 2000. According to previous descriptions of host range, symptoms, and spore morphology, the pathogen was identified as the microcyclic rust fungus, Puccinia xanthii Schwein. (2-4). Telia, reaching 9 mm in diameter and often coalescing to form larger lesions associated with chlorosis, occurred on the lower surface of leaves. Symptoms were first observed at the V-12 growth stage when approximately 40% of leaves displayed lesions. The disease subsequently spread to younger plants (V-2 stage) where an incidence of 100% was recorded. Severity estimates regularly reached 50% leaf area affected. The primary source of inoculum was thought to be nearby rust-infected Xanthium strumarium sensu lato (burweed or cocklebur) plants, a known host for P. xanthii (2,4). Infection studies were carried out on 3-week-old sunflower plants using a mini settling tower supporting an inverted water agar plate containing leaf disks with P. xanthii telia (2) obtained from either sunflower or burweed. Plants covered with a settling tower were kept in the dark in a dew chamber for 48 h. Microscopic examination of inoculum from both sources confirmed germination of teliospores and formation of basidiospores. Test entries had similar disease reactions regardless of whether inocula were collected from H. annuus or X. strumarium. Fleck symptoms were visible on the hybrids SNK 77 and Orit 5 days after placing plants in the dew chamber. On these entries, telia gradually increased in size, indicating susceptibility to P. xanthii. Furthermore, those leaves receiving high inoculum dosages were desiccated 11 days after inoculation. Hybrids Hysun 333 and CRN 1470 and the male sterility maintainer lines DC 4 and RK 74 produced resistant reactions. Hyperplasia of stem and petiole tissue was observed on certain Orit, DC 4, and CRN 1470 plants. Susceptibility of burweed, a common and widespread annual weed in southern Africa (1), to a sunflower isolate of P. xanthii, was also confirmed. Depending on the formation of teliospores, the identity of the causal organism was verified in all inoculation studies. P. xanthii damage on sunflower has not been reported from South Africa. However, the disease has now become economically important as severe foliar lesions rendered plants unacceptable for the ornamental sunflower market. References: (1) C. Bromilow. 1995. Problem Plants of South Africa. Briza Publications, Pretoria, South Africa. (2) L. Morin et al. Can. J. Bot. 71:959, 1993. (3) L. Morin et al. Mycol. Res. 96:661, 1992. (4) J. Parmelee. Can. J. Bot. 47:1391, 1969.
SEVERAL STUDIES HAVE BEEN CONDUCTED on the presence and diversity of airborne fungal spores in residential and occupational areas. This is the first investigation on this topic in the mining environment. The impact of fungi-especially as opportunistic pathogens-on their health and productivity needs to be assessed, considering the compromised health of a large number of HIV-infected miners in South Africa. Accordingly, the aim of this study was to determine the abundance of fungal spores as well as the diversity of culturable airborne fungi in an active gold mine. The results indicate that three of the sampled sites in the mine contain abundant numbers of culturable airborne fungi. The first site was next to an auxiliary extraction fan, which could act as an accumulator for airborne fungal spores from the rest of the mine. The two other sites had high human activity, disturbances from which may contribute to an elevated fungal load in the air. The presence of timber supports at one site may serve as a growth substrate for several fungal genera. The diversity of filamentous fungal genera increased from outside the mine to deeper into the mine, whereas the diversity of yeast genera followed an opposite trend, with no yeasts detected deep in the mine. Although most of the isolates identified are not pathogens, they could still have a negative impact (either as opportunistic pathogens or allergens) on workers, especially immunocompromised persons if exposed to them for prolonged periods.
Canna indica L., known as Indian shot or canna lily, occurs throughout the New World in tropical and subtropical areas. This upright, perennial, rhizomatous herb is a popular garden plant in South Africa because of its spectacular plant habit and growth vigor. During January 2005, canna lily leaves with rust symptoms were collected from Pietermaritzburg in the province of KwaZulu-Natal. Orange-yellow uredinia were observed primarily on the abaxial surfaces, often covering the entire leaf with coalescing pustules. Koch's postulates were completed in repeated tests with spray inoculations of blooming potted plants, urediniospores suspended in water (42 × 10 4 spores/ml), incubation in a dew chamber for 14 h at 20°C in the dark, and then returned to the greenhouse. Symptoms similar to those of the original collection formed 10 days postinoculation. Only the uredinial stage was observed, which was characterized by hypophyllous, yellow-brown, subepidermal, erumpent, and irregular shaped uredinia. The urediniospores were round to ovoid, orange-yellow, echinulate, and 25 to 35 × 15 to 20 μm. The pathogen was identified as Puccinia thaliae Diet. according to its description on Canna edulis Ker-Gawl. (1). Following the report of P. thaliae on C. indica in Hawaii in 1989 (2), to our knowledge, this is the first description of canna lily rust in South Africa. References: (1) M. L. Jeeva et al. Plant Pathol. 53:261, 2004. (2) D. E. Gardner and C. S. Hodges. Pac. Sci. 43:4155, 1989.
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