scholarly journals A Survey for ‘Candidatus Liberibacter’ Species in South Africa Confirms the Presence of Only ‘Ca. L. africanus’ in Commercial Citrus

Plant Disease ◽  
2010 ◽  
Vol 94 (2) ◽  
pp. 244-249 ◽  
Author(s):  
G. Pietersen ◽  
E. Arrebola ◽  
J. H. J. Breytenbach ◽  
L. Korsten ◽  
H. F. le Roux ◽  
...  
Keyword(s):  
South Africa ◽  
Western Cape ◽  
Chain Reaction ◽  
Citrus Production ◽  
Candidatus Liberibacter ◽  
Citrus Orchards ◽  
Polymerase Chain ◽  
Serious Disease ◽  
Production Areas ◽  
Representative Samples

Greening disease of citrus is a serious disease known in South Africa since the late 1920s. In South Africa, it is associated with infection by ‘Candidatus Liberibacter africanus’, a heat sensitive, phloem-limited, noncultured alpha-proteobacterium. Huanglongbing (HLB), a similar, but more devastating disease that was described initially from China but which now occurs in several citrus producing countries, is associated with a different Liberibacter species, ‘Ca. L. asiaticus’. A ‘Ca. L. africanus’ subspecies, ‘Ca. L. africanus subsp. capensis’, has been found only in South Africa infecting an indigenous Rutaceous species, Calodendrum capense (Cape Chestnut), in the Western Cape in 1995. The discovery of a new Liberibacter species in Brazil, ‘Ca. L. americanus’, and the spread of ‘Ca. L. asiaticus’ to a number of additional countries over the last few years prompted us to assess whether only ‘Ca. L. africanus’ is present in commercial citrus orchards in South Africa. Samples displaying greening or similar symptoms were collected from 249 citrus trees from 57 orchards distributed throughout the greening affected citrus production areas of South Africa. Multiplex polymerase chain reaction (PCR) was performed on DNA extracts to detect the known citrus Liberibacters. Amplicons were obtained from 197 samples. None of the samples yielded a 1,027-bp amplicon indicative of ‘Ca. L. americanus’ infection. The amplicons of 84 samples were sequenced, and all were identical to the cognate ‘Ca. L. africanus’ Nelspruit sequence in GenBank. No instance of ‘Ca. L. asiaticus’ or ‘Ca. L. africanus subsp. capensis’ sequence was found. Geographically representative samples that tested negative for Liberibacter also tested negative for phytoplasmas based on real-time PCR results. Based on the results of this survey, it is concluded that to date only ‘Ca. L. africanus’ is associated with citrus greening in commercial citrus in South Africa.

scholarly journals Psittacine beak and feather disease virus in budgerigars and ring-neck parakeets in South Africa

2004 ◽  
Vol 71 (1) ◽  
Author(s):  
J. Albertyn ◽  
K.M. Tajbhai ◽  
R.R. Bragg
Keyword(s):  
South Africa ◽  
Polymerase Chain Reaction ◽  
Genetic Variation ◽  
Disease Virus ◽  
Common Disease ◽  
Sample Collection ◽  
Chain Reaction ◽  
Polymerase Chain ◽  
Feather Disease Virus ◽  
Viral Isolates

Psittacine beak and feather disease (PBFD) is a common disease of the psittacine species and is caused by the psittacine beak and feather disease virus (PBFDV). In this study the occurrence of the disease in ring-neck parakeets and budgerigars in South Africa suffering from feathering problems, using polymerase chain reaction as a diagnostic test was investigated. The genetic variation between viral isolates was also studied. Results indicate that PBFDV can be attributed to being the cause of feathering problems in some of the ring-neck parakeets and budgerigars in South Africa. Genetic variation of isolates occurs between species and individuals. A cheap and easy to use method of blood sample collection on filter paper for diagnostic purposes was also evaluated. It proved to be less stressful to the birds and did not inhibit further processes.

scholarly journals In Planta Distribution of ‘Candidatus Liberibacter asiaticus’ as Revealed by Polymerase Chain Reaction (PCR) and Real-Time PCR

2008 ◽  
Vol 98 (5) ◽  
pp. 592-599 ◽  
Author(s):  
Satyanarayana Tatineni ◽  
Uma Shankar Sagaram ◽  
Siddarame Gowda ◽  
Cecile J. Robertson ◽  
William O. Dawson ◽  
...  
Keyword(s):  
Polymerase Chain Reaction ◽  
Real Time ◽  
Real Time Pcr ◽  
Citrus Tree ◽  
Candidatus Liberibacter Asiaticus ◽  
In Planta ◽  
Chain Reaction ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Polymerase Chain

Huanglongbing (HLB) is one of the most devastating diseases of citrus worldwide, and is caused by a phloem-limited fastidious prokaryotic α-proteobacterium that is yet to be cultured. In this study, a combination of traditional polymerase chain reaction (PCR) and real-time PCR targeting the putative DNA polymerase and 16S rDNA sequence of ‘Candidatus Liberibacter asiaticus,’ respectively, were used to examine the distribution and movement of the HLB pathogen in the infected citrus tree. We found that ‘Ca. Liberibacter asiaticus’ was distributed in bark tissue, leaf midrib, roots, and different floral and fruit parts, but not in endosperm and embryo, of infected citrus trees. Quantification analysis of the HLB bacterium indicated that it was distributed unevenly in planta and ranged from 14 to 137,031 cells/μg of total DNA in different tissues. A relatively high concentration of ‘Ca. Liberibacter asiaticus’ was observed in fruit peduncles. Our data from greenhouse-infected plants also indicated that ‘Ca. Liberibacter asiaticus’ was transmitted systemically from infection site to different parts of the plant. Understanding the distribution and movement of the HLB bacterium inside an individual citrus tree is critical for discerning its virulence mechanism and to develop management strategies for HLB.

Steinernema citrae n. sp. (Rhabditida: Steinernematidae), a new entomopathogenic nematode from South Africa

Nematology ◽  
2011 ◽  
Vol 13 (5) ◽  
pp. 569-587 ◽  
Author(s):  
Nomakholwa F. Stokwe ◽  
Antoinette P. Malan ◽  
Khuong B. Nguyen ◽  
Rinus Knoetze ◽  
Louwrens Tiedt
Keyword(s):  
South Africa ◽  
New Species ◽  
Body Length ◽  
Entomopathogenic Nematode ◽  
Tail Length ◽  
Morphological Characters ◽  
The Body ◽  
Infective Juvenile ◽  
Western Cape ◽  
Citrus Orchards

Abstract During a survey for entomopathogenic nematodes in citrus orchards throughout South Africa, a new species of Steinernema was isolated from a citrus orchard on Rietkloof farm, near the town of Piketberg in the Western Cape Province, South Africa. The nematode was isolated from soil using the Galleria-baiting technique. Steinernema citrae n. sp. is characterised by the following morphological characters: third-stage infective juvenile with a body length of 754 (623-849) μm, distance from head to excretory pore of 56 (49-64) μm, tail length of 71 (63-81) μm, and ratio E value of 110 (85-132). The lateral pattern for the new species is 2, 7, 8, 6, 4, 2 and is not typical for the genus. Steinernema citrae n. sp. is closely related the feltiae-group. The body length of the IJ is close to that of S. texanum and S. weiseri, though it differs in body diam., the length of the pharynx and E%. The male of S. citrae n. sp. differs from S. feltiae in the length and shape of the spicule and body diam. Steinernema citrae n. sp. differs from all species in the feltiae-group in the morphology of the vulva, as it has a single flapped, low, epiptygma. It also differs from the most closely related species, S. feltiae, as there is no interbreeding between the two species. In addition, the new nematode differs from other species of the feltiae-group by characteristics of the ITS and D2D3 regions of its rDNA.

scholarly journals A New Pathotype of Puccinia striiformis f. sp. tritici on Wheat in South Africa

Plant Disease ◽  
1999 ◽  
Vol 83 (6) ◽  
pp. 591-591 ◽  
Author(s):  
W. H. P. Boshoff ◽  
Z. A. Pretorius
Keyword(s):  
South Africa ◽  
Stripe Rust ◽  
Puccinia Striiformis ◽  
Single Step ◽  
Western Cape ◽  
Monogenic Resistance ◽  
Major Resistance Gene ◽  
New Variant ◽  
Production Areas ◽  
Wheat Lines

Following the detection of Puccinia striiformis f. sp. tritici for the first time on wheat (Triticum aestivum) in the Western Cape in August 1996, stripe rust has spread to all the important wheat production areas in South Africa. Only the introduced pathotype (pt. 6E16) was detected in surveys of these areas during 1996 and 1997. In 1998, a severe stripe rust epidemic occurred in the eastern Free State on the extensively grown cultivars Hugenoot and Carina, both which are resistant to pt. 6E16. Stripe rust severities of 100% were common on flag and lower leaves, and widespread applications of fungicides were necessary. Avirulence/virulence characteristics of P. striifomis f. sp. tritici isolates collected from Hugenoot and Carina were determined on 17 standard stripe rust differential wheat lines and 11 supplementary testers. The latter testers included the wheat lines TP981 and TP1295 (supplied by R. Johnson, Cambridge, UK), both of which have a major resistance gene in common with the differentials Heines Peko, Reichersberg 42, Strubes Dickkopf, Clement, and Heines VII (1). Isolates obtained from Hugenoot and Carina differed from pt. 6E16 based on virulence to Reichersberg 42 (Yr7,25), Heines Peko (Yr2,6,25), TP981 (Yr25), and TP1295 (Yr25). The new variant, designated as 6E22, was also identified in collections from the province KwaZulu-Natal. Seedling tests with 6E16 and 6E22 have shown that Hugenoot, Carina, and Tugela-DN are the only local cultivars affected by the new pathotype. The occurrence of pt. 6E22, which appears to be a single-step adaptation from 6E16 adding virulence to Yr25, emphasizes the vulnerability of monogenic resistance to this disease. Reference: (1) R. A. McIntosh et al. Wheat Inform. Serv. 85:56, 1997.

Population genetic analyses of Phytophthora cinnamomi reveals three lineages and movement between natural vegetation and avocado orchards in South Africa

2022 ◽  
Author(s):  
Juanita Engelbrecht ◽  
Tuan A. Duong ◽  
Trudy Paap ◽  
Joseph Michael Hulbert ◽  
Juanita Joyce Hanneman ◽  
...  
Keyword(s):  
South Africa ◽  
Genetic Diversity ◽  
Phytophthora Cinnamomi ◽  
Resistance Breeding ◽  
Natural Vegetation ◽  
Economic Losses ◽  
Western Cape ◽  
Natural Ecosystems ◽  
Agricultural Industries ◽  
Production Areas

Phytophthora cinnamomi is the causal agent of root rot, canker and dieback of thousands of plant species around the globe. This oomycete not only causes severe economic losses to forestry and agricultural industries, but also threatens the health of various plants in natural ecosystems. In this study, 380 isolates of P. cinnamomi from four avocado production areas and two regions of natural vegetation in South Africa were investigated using 15 microsatellite markers. These populations were found to have a low level of genetic diversity and consisted of isolates from three lineages. Shared genotypes were detected between isolates from avocado orchards and natural vegetation, indicating the movement of isolates between these areas. The population from the Western Cape natural vegetation had the highest genotypic diversity and unique alleles, indicating this could be the point of introduction of P. cinnamomi to South Africa. Index of association analysis suggested that five out of six populations were under linkage disequilibrium suggesting a clonal mode of reproduction whereas genotypes sampled from a recently established avocado orchard in the Western Cape were derived from a randomly recombined population. This study provided novel insights on the genetic diversity and spread of P. cinnamomi in South Africa. It also reported on the predominance of triploidy in natural occurring populations and provided evidence for recombination of P. cinnamomi for the first time. The presence of two dominant genotypes in all avocado production areas in South Africa highlight the importance of considering them in disease management and resistance breeding programmes.

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