scholarly journals Characterization of Rhizoctonia spp. Recovered from Crop Plants Used in Rotational Cropping Systems in the Western Cape Province of South Africa

Plant Disease ◽  
2006 ◽  
Vol 90 (11) ◽  
pp. 1399-1406 ◽  
Author(s):  
Y. T. Tewoldemedhin ◽  
S. C. Lamprecht ◽  
A. McLeod ◽  
M. Mazzola
Keyword(s):  
South Africa ◽  
Crop Production ◽  
Optimal Time ◽  
Limiting Factor ◽  
Western Cape ◽  
Optimum Growth ◽  
Western Cape Province ◽  
Binucleate Rhizoctonia ◽  
Weakly Virulent

Isolates of Rhizoctonia spp. associated with barley, canola, clover, lucerne, lupin, annual Medicago spp. (medic), and wheat were recovered during the conduct of a 4-year (2000 to 2003) crop rotation trial in the Western Cape province of South Africa. These isolates were characterized by determining their anastomosis group (AG), in vitro optimum growth temperature, and pathogenicity toward emerging and 14-day-old seedlings of all the aforementioned crops. During the 4-year rotational trial, 428 Rhizoctonia isolates, in all, were obtained. The most abundant multinucleate AG was AG-4 HG-II (69%), followed by AG-2-1 (19%), AG-3 (8%), AG-2-2 (2%), and AG-11 (2%). The population of binucleate Rhizoctonia spp. comprised AG-K (53%), AG-A (10%), AG-I (5%), and unidentified AGs (32%). The optimal time for isolating Rhizoctonia spp. was found to be at the flowering or seedpod stage (20 to 22 weeks after planting). Temperature studies showed that isolates belonging to AG-2-2, AG-4 HG-II, and AG-K had significantly higher optimum growth temperatures than those from other AGs. In pathogenicity assays conducted on emerging as well as 14-day-old seedlings, isolates of AG-2-2 and AG-4 HG-II were the most virulent on all crops. Rhizoctonia solani AG-2-1 was highly virulent on canola, moderately virulent on medic and lupin, weakly virulent on lucerne and barley, and nonpathogenic on wheat. AG-11 isolates were moderate to weakly virulent on all crops, with the exception of barley and wheat. AG-3 was weakly virulent on canola, lupin, and medic. AG-K was the only binucleate Rhizoctonia sp. capable of inciting disease in our assays. This is the first comprehensive study to elucidate the identity and potential importance of Rhizoctonia spp. as a yield limiting factor in crop production systems in the Western Cape province of South Africa.

scholarly journals Extent of Soil Acidity in No-Tillage Systems in the Western Cape Province of South Africa

Land ◽  
2020 ◽  
Vol 9 (10) ◽  
pp. 361
Author(s):  
Adriaan Liebenberg ◽  
John Richard (Ruan) van der Nest ◽  
Ailsa G. Hardie ◽  
Johan Labuschagne ◽  
Pieter Andreas Swanepoel
Keyword(s):  
South Africa ◽  
Crop Production ◽  
Acid Soils ◽  
Soil Survey ◽  
Annual Rainfall ◽  
Western Cape ◽  
No Tillage ◽  
Western Cape Province ◽  
Tillage Systems ◽  
Depth Increment

Roughly 90% of farmers in the Western Cape Province of South Africa have converted to no-tillage systems to improve the efficiency of crop production. Implementation of no-tillage restricts the mixing of soil amendments, such as limestone, into soil. Stratification of nutrients and pH is expected. A soil survey was conducted to determine the extent and geographical spread of acid soils and pH stratification throughout the Western Cape. Soil samples (n = 653) were taken at three depths (0–5, 5–15, 15–30 cm) from no-tillage fields. Differential responses (p ≤ 0.05) between the two regions (Swartland and southern Cape), as well as soil depth, and annual rainfall influenced (p ≤ 0.05) exchangeable acidity, Ca and Mg, pH(KCl), and acid saturation. A large portion (19.3%) of soils (specifically in the Swartland region) had at least one depth increment with pH(KCl) ≤ 5.0, which is suboptimal for wheat (Triticum aestivum), barley (Hordeum vulgare), and canola (Brassica napus). Acid saturation in the 5–15 cm depth increment in the Swartland was above the 8% threshold for production of most crops. Acid soils are a significant threat to crop production in the region and needs tactical agronomic intervention (e.g. strategic tillage) to ensure sustainability.

scholarly journals Rhizoctonia Anastomosis Groups Associated with Diseased Rooibos Seedlings and the Potential of Compost as Soil Amendment for Disease Suppression

Plant Disease ◽  
2015 ◽  
Vol 99 (7) ◽  
pp. 1020-1025 ◽  
Author(s):  
Y. T. Tewoldemedhin ◽  
S. C. Lamprecht ◽  
M. Mazzola
Keyword(s):  
South Africa ◽  
Internal Transcribed Spacer ◽  
Anastomosis Group ◽  
Disease Suppression ◽  
Western Cape ◽  
Damping Off ◽  
Western Cape Province ◽  
Internal Transcribed Spacer Region ◽  
Binucleate Rhizoctonia ◽  
Compost Amendment

Rhizoctonia spp. associated with rooibos in the Western Cape province of South Africa were recovered during the 2008 season by planting seedlings in rhizosphere soils collected from 14 rooibos nurseries. In all, 75 Rhizoctonia isolates were obtained, of which 67 were multinucleate and 8 were binucleate Rhizoctonia spp. The identity of these isolates to anastomosis group (AG) was determined through sequence analysis of the ribosomal DNA internal transcribed spacer region. The collection of multinucleate isolates included representatives of AG-2-2 (67%), AG-4 HGI (14%), AG-11 (5%), and R. zeae (3%). Binucleate AGs included AG-Bo (4%) and AG-K (4%) and an unidentified binucleate Rhizoctonia (3%). Rhizoctonia solani AG-2-2 was the most widely distributed species of Rhizoctonia detected among the 11 nurseries sampled. All AGs recovered from rooibos have been previously reported on crop plants in South Africa, with the exception of R. zeae. However, this is the first study to classify the Rhizoctonia AGs recovered from rooibos. In glasshouse bioassays, the most virulent Rhizoctonia AGs on rooibos and lupin were AG-2-2, AG-4 HGI, and AG-11. Although plant damage was less than that observed for lupin and rooibos, oat was significantly affected by AG-2-2 and AG-4 HGI. Two composts sourced from independent suppliers were evaluated for disease suppression under glasshouse conditions. Compost amendment suppressed damping-off by most R. solani AGs, except for AG-4 HGI. Furthermore, within AG-2-2, suppression by compost was isolate specific.

scholarly journals First Report of Togninia minima Perithecia on Esca- and Petri-Diseased Grapevines in South Africa

Plant Disease ◽  
2013 ◽  
Vol 97 (9) ◽  
pp. 1247-1247 ◽  
Author(s):  
M. A. Baloyi ◽  
F. Halleen ◽  
L. Mostert ◽  
A. Eskalen
Keyword(s):  
South Africa ◽  
Western Cape ◽  
Sterile Water ◽  
Western Cape Province ◽  
First Report ◽  
Phaeomoniella Chlamydospora ◽  
Petri Disease ◽  
General Decline ◽  
Spore Release

Esca and petri diseases are important grapevine trunk diseases in South Africa and most other grape-producing countries. The causal pathogens are Phaeomoniella chlamydospora and several species of Phaeoacremonium. In total, 25 species of Phaeoacremonium have been isolated from grapevines of which seven species have been linked to Togninia teleomorphs obtained through in vitro mating studies (3). Of these species, only perithecia of T. minima, T. fraxinopennsylvanica, and T. viticola have been found on grapevines in California (1,2,4). T. minima is heterothallic, and although both mating types are present in South African vineyards, perithecia have never been observed (3). In the current study, grapevine cordons and trunks were collected from vineyards and rootstock mother vines within Western Cape Province for examination in the laboratory under a dissecting microscope. The grapevines displayed general decline symptoms, including reduced vegetative growth, dead or dying shoots and cordons, as well as internal vascular streaking and/or a red/black/brown margin next to decayed wood typically associated with esca and petri disease. Rootstock mother vines were apparently healthy, although many old, cracked pruning wounds were visible. Togninia-like perithecia with distinctive long necks were found along the wood crevices, often on old pruning wounds. The perithecia were removed and placed on microscope slides with sterile water. Structures were measured and slides were washed with 500 μl of sterile water onto potato dextrose agar amended with chloramphenicol (250 mg/liter). Ascospores were allowed to germinate overnight to obtain single ascospore colonies. Perithecia were found on cultivars Muscat d' Alexandrie and Pinotage (Vitis vinifera) at Stellenbosch in May 2011 and on Ramsey (V. champinii) rootstock mother vines at Slanghoek in June 2012. Perithecia were globose to subglobose, black, and often embedded in the wood tissue but also present on the surface of the wood. The length of the necks was 250 to 300 × 47.5 to 55 μm. The asci were hyaline and ranged from 16 to 25 × 3.5 to 5 μm. Ascospores were hyaline, ellipsoid, and ranged from 5 to 6 × 1.5 to 2 μm. These measurements were similar to those reported by Mostert et al. (3) and Rooney et al. (4). Colony growth was typical of T. minima. DNA was extracted from the colonies and the partial betatubulin gene was amplified and sequenced using the primers T1 and Bt2b. Sequences were deposited into GenBank (JX962864 to 67). Based on a megablast search of the NCBI's GenBank nucleotide database, 100% similarity was found with other T. minima sequences (JQ691670.1, HQ605018.1, HQ605014.1; identities = 647/647 [100%], gaps = 0/647 [0%]). To our knowledge, this is the first report on the occurrence of T. minima perithecia on grapevines in Western Cape Province of South Africa. The removal of dead spurs and cordons will be instrumental in lowering the inoculum originating from perithecia, especially in rootstock mother blocks where no control strategies are applied for petri disease or esca. Spore trapping studies are currently in progress to study spore release patterns in order to determine whether pruning wounds are at risk during traditional pruning periods. References: (1) A. Eskalen et al. Plant Dis. 89:528, 2005. (2) A. Eskalen et al. Plant Dis. 89:686, 2005. (3) L. Mostert et al. Stud. Mycol. 54:1, 2006. (4) S. Rooney-Latham et al. Plant Dis. 89:867, 2005.

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