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The production of malting barley under dryland and irrigated environments in South Africa (SA) has increased recently, making it the second most important winter crop after wheat. To assess the potential vulnerability of adapted barleys from SA to wheat stem rust (caused by Puccinia graminis f. sp. tritici, Pgt, race PTKST) and rye stem rust (Puccinia graminis f. sp. secalis, Pgs, isolate UVPgs1), 50 accessions were evaluated as seedlings and as adult plants. The same barley germplasm was tested against Pgt and Pgs cultures from the USA that have proven useful for detecting the stem rust resistance genes Rpg1 and the rpg4/Rpg5 complex. The possible presence of these resistance genes was assayed using molecular markers and sequence analysis. Barley accessions exhibited mostly resistant infection types (ITs) to the South African cultures, whilst field data revealed that several of the barley varieties displayed high severities in combination with more compatible host response types to race PTKST. The barley accessions exhibited mostly high ITs to cultures from the USA. None of the seedling IT data was sufficiently distinct to reliably postulate the presence of possible resistance genes. This result was corroborated from the molecular assays for Rpg1 and rpg4/Rpg5. Except for one line that tested heterozygous for the Rpg1 gene, none of the test entries contained this gene or a functional rpg4/Rpg5 complex due to the prevalence of mutations in the rpg4/Rpg5 + carriers. Susceptibility among barley varieties to wheat stem rust race PTKST under field conditions in the present study is of concern.

Barley, host to the wheat and rye attacking forms of the stem rust pathogen, Puccinia graminis (Pg), is considered inherently more resistant to Pg than wheat. To investigate whether this enhanced basal defence is associated with early infection or colonisation processes, adult plants of selected barley and wheat entries were inoculated with Pg f. sp. tritici (Pgt) races BNGSC and PTKST, and Pg f. sp. secalis (Pgs) isolate UVPgs1. Flag leaf sheaths on the last stem internode were sampled for analysis. Using scanning electron microscopy and epidermal stripping, early Pg infection structure development was compared between barley and wheat. Sub-stomatal vesicle appearance and production of haustorial mother cells were similar at 24 and 48 h post inoculation (hpi), respectively. Significant variation occurred among host entries (P ≤ 0.01) for colony size and fungal biomass at 120 hpi. Differences between the Pgt races and the Pgs isolate as well as the host entry-Pg isolate interaction proved insignificant (P ≥ 0.05). The period between 120 and 240 hpi may hold some explanation for the perceived lower stem rust receptivity in barley, since a steep increase in accumulated fungal biomass observed in the susceptible wheat Line 37 − 07 was not seen in the susceptible barley entries at the same time interval.

Puccinia graminis f. sp. avenae (Pga) samples were collected from cultivated oat (Avena sativa L.) in trial plots and commercial fields and from wild oat (Avena spp.) during the 2016 and 2017 seasons. Field samples were purified through selection of single pustule isolates and subsequent urediniospore increases using the susceptible cultivar Swan. For race phenotyping, a set of 12 international differential lines was used that resulted in the identification of races RSJ, RJS and RJJ. Race RSJ was the most prevalent (60% of isolates) followed by races RJS (34%) and RJJ (6%). These races varied in virulence for Pg6 and Pg12, with no avirulence recorded for Pg1, 2, 4, 8, 9, 13 and Pg15 and no virulence for Pg3, 10 and Pg16. Seedling infection types of 32 oat cultivars to the three described races showed compatible phenotypes for all cultivars towards at least one of the races. Moderate levels of adult plant resistance against races RJS and RSJ were recorded for seven cultivars during field tests in 2017 and 2018. Thirteen microsatellite markers used to assess genetic variability amongst twenty four field isolates revealed three sub-populations of which only one correlated with the race phenotype. The results contributed to our understanding of the diversity of the Pga population in South Africa, including useful resistance sources and cultivar responses.

Triticale is derived from a cross between wheat and rye and the leaf rust pathogen of wheat, Puccinia triticina (Pt), and that of rye, P. recondita sensu stricto (Pr), can potentially cause disease in this crop. Recent studies showed that wheat rust fungi could adapt to warmer temperatures. In this paper, we report on the comparative virulence of three Pt races and one Pr isolate (all were collected in South Africa) on triticale as well as their in vitro response to temperature. Seedling infection types (SITs) of 169 triticale entries to Pt races 3SA144 (North American code SDDN), 3SA145 (CCPS) and 3SA248 (CFPS) and Pr isolate UVPr2 revealed that 3SA144 is the most virulent with 106 triticale entries found susceptible to this race. The three Pt races were avirulent to the four rye cultivars included as controls. UVPr2 was avirulent on all the triticale entries and 49 entries were considered resistant to the Pt races tested. Freshly harvested urediniospores of the above isolates were tested at constant temperature regimes of 10 °C, 22.5 °C and 35 °C to study germination characteristics. Mean urediniospore germination percentages as determined for 3SA144 (61.3%) and UVPr2 (62.6%) were significantly lower when compared to 3SA145 (83.7%) and 3SA248 (84.9%). Race 3SA144 was most sensitive to the higher temperature regime of 35 °C (5.2% germination). Among the investigated races, 3SA144 showed significantly lower mean germ tube elongation rates at all three incubation temperatures. This is the first report of differences in temperature adaptation between Pt races from SA.

Traditional race phenotyping of cereal rusts is based on the pathogenicity of field isolates on seedlings using a set of differential host lines. These lines are regularly planted in the field, often as part of trap nurseries. In trap nurseries the primary objective is to assess the occurrence of isolates with virulence or avirulence on key resistance genes. Although it is generally accepted that field nurseries cannot be used for race identification, the correlation between seedling and adult plant response of commonly used stem rust differential lines needs further clarification. To determine if any of the wheat stem rust differential lines in South Africa contains unknown genes for adult plant resistance, or are poorly expressed in the adult stage, entries were assessed over four seasons in a nursery inoculated with race PTKST of Puccinia graminis f. sp. tritici. A strong correlation between seedling infection type and field response occurred for differential lines carrying Sr5, 6, 7b, 8a, 8b, 9a, 9b, 9d, 9e (Vernstein), 10, 11, 24, 27, 31, 36, 38, 44, McN, Kw, and Satu. However, differential lines carrying Sr9e (Vernal), 9g (Acme), 30 (Festiguay), and Sr17 (Renown) failed to accurately predict virulence under epidemic conditions in the field. Importantly, higher than expected severity and response types were recorded for differential lines carrying SrTmp and Sr21, especially under prolonged epidemic conditions. It can be concluded that field ratings of the current set of South African stem rust differential lines do not accurately describe P. graminis f. sp. tritici race PTKST.

Race 2SA55 of the wheat stem rust pathogen, Puccinia graminis f. sp. tritici, was described for the first time during 2000 in South Africa. This race is of particular interest as it was the first local report of increased virulence towards barley cultivars by wheat stem rust. Using three original accessions of 2SA55 from the rust collection of the University of the Free State, nine single pustule isolates were established. Phenotyping of isolates to characterise 2SA55 according to the North American nomenclature system revealed variation in virulence for Sr9g on the tester lines Kubanka and Acme, which was not detected in the initial description of 2SA55. Seven isolates coded as BNGSC, which except for virulence on Sr9b resembled the initial avirulence/virulence description for 2SA55. The remaining two isolates with Sr9g virulence coded as BPGSC. The seedling infection types for the two 2SA55 derived races BNGSC and BPGSC on the Stakman differential set as well as on an extended set of Sr lines and 144 South African wheat cultivars and advanced breeding lines revealed no further distinction in reaction between them. Microsatellite analysis indicated that while race BN/PGSC shares phenotypic similarity with several of the South African non-Ug99 races, it was genetically distinct.

Virulence analysis of the South African Puccinia triticina Eriks. population from 2012 to 2016 revealed the presence of four new wheat (Triticum aestivum L.) leaf rust races, which coincided with the increased incidence of the disease during this period. Considering their infection types on 43 differential wheat entries, three of the new races namely 3SA10 (North American code CFPS), 3SA38 (CDPS) and 3SA248 (CFPS) were found to be similar to each other, and only varied in virulence for Lr20 and Lr26 whereas race 3SA115 (CBPS) was more avirulent. This was confirmed when seedling infection type data for 117 South African wheat cultivars and advanced breeding lines revealed that only 35 of the entries are susceptible to race 3SA115. Races 3SA10 (77 entries susceptible), 3SA38 (68) and 3SA248 (78) showed increased virulence when compared with the 51 entries susceptible to race 3SA145 (CCPS) which dominated in frequency during 2012 to 2016. SSR analysis confirmed the close genetic relationships between the four new races and race 3SA145. The results verified the adaptability of the leaf rust pathogen and by acquiring virulence for Lr24, the new races 3SA10, 3SA38 and 3SA248 are considered to become more prevalent and threatening compared to the current dominating race 3SA145.

The wheat leaf rust fungus, Puccinia triticina, is found in the major wheat growing regions of the world and is a leading cause of yield loss in wheat. Populations of P. triticina are highly variable for virulence to resistance genes in wheat and adapt quickly to resistance genes in wheat cultivars. The objectives of this study were to determine the genetic relatedness of worldwide collections of P. triticina using restriction site associated genotyping by sequencing. A total of 558 isolates of P. triticina from wheat producing regions in North America, South America, Europe, the Middle East, Ethiopia, Russia, Pakistan, Central Asia, China, New Zealand, and South Africa were characterized at 6745 single nucleotide loci. Isolates were also tested for virulence to 20 near-isogenic lines that differ for leaf rust resistance genes. Populations that were geographically proximal were also more closely related for genotypes. In addition, groups of isolates within regions that varied for genotype were similar to groups from other regions, which indicated past and recent migration across regions. Isolates from tetraploid durum wheat in five different regions were highly related with distinct genotypes compared to isolates from hexaploid common wheat. Based on a molecular clock, isolates from durum wheat found only in Ethiopia were the first to diverge from a common ancestor form of P. triticina that is found on the wild wheat relative Aegilops speltoides, followed by the divergence of isolates found worldwide that are virulent to durum wheat, and then by isolates found on common wheat.

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.

To determine phenotypic diversity of Puccinia graminis f. sp. tritici (Pgt) , the cause of stem rust of wheat, samples of infected stems were collected during 2009–2013 from commercial wheat fields, experimental plots, and rust trap nurseries across major wheat growing regions of South Africa (SA). Pgt races were identified based on their avirulence/virulence profiles on seedlings of 20 standard and five supplemental differential lines. Nine Pgt races were identified from 521 isolates pathotyped. Predominant races were TTKSF (2SA88, South African race notation) with 39%–85% frequency and BPGSC + Sr27 , Kiewiet , Satu (2SA105) with 10%–20% frequency. Race TTKSF is virulent on major resistance genes such as Sr5 , Sr6 , Sr9e , and Sr38 and is one of the variants of the highly virulent Ug99 race group originally detected in East Africa. Race TTKSP (2SA106), also a member of the Ug99 lineage, was detected in 2009 and 2010. A new race virulent on Sr31 , PTKST (2SA107), was detected in 2009. Two new races, TTKSF + Sr9h (2SA88 + Sr9h ) and BFBSC (2SA108), were identified in 2010. Race TTKSF + Sr9h is similar to TTKSF except for its virulence on Sr9h . Race BFBSC appears related to Pgt races characterized by avirulence for Sr5 and often attacking triticale. Simple sequence repeat (SSR) analysis indicated that race BFBSC forms part of the non-Ug99 group of South African Pgt races. Despite some similarity in avirulence/virulence phenotype with the non-Ug99 races, BFBSC represents a third distinct genetic lineage within this group. Genes Sr13 , 14 , 22 , 25 , 26 , 29 , 32 , 33 , 35 , 36 , 37 , 39 , 42 , and 43 that are effective against the new and other Pgt races can be used in resistance breeding in SA. Races like PTKST and TTKSF + Sr9h were also reported in other Southern African countries suggesting that they probably spread to SA from neighbouring regions. The new races are additions to nearly 30 Pgt races identified since the early 1980s, and suggest continued variability of the Pgt population in SA. Therefore, surveys should be conducted regularly to timely detect and manage new races, and utilize the latter in screening and identification of effective sources of resistance.

Screening for adult plant resistance in wheat to stem rust, caused by Puccinia graminis f. sp. tritici, is generally conducted in field plots. Although such evaluations are successful if managed properly, field ratings are time consuming, expensive, weather dependent, and open to inoculum of unwanted races or other confounding diseases. The objective of this study was to develop a dependable system of screening the response of adult plants to stem rust under greenhouse conditions. A comparison of inoculation methods and incubation environments showed that plants inoculated with urediniospores suspended in water, followed by a 24 h dew period in a plastic chamber constructed in a greenhouse, gave the most consistent results. Measurements of response type, stem rust severity, and frequency in follow-up experiments indicated that the most reliable infection was obtained when plants sprayed with 1.25 mg urediniospores per ml water were incubated in the plastic chamber. Using the optimized protocol, a Kariega × Avocet S doubled haploid population was inoculated with two P. graminis f. sp. tritici races. Depending on the race, composite interval mapping showed flag leaf infection type to be significantly influenced by regions on chromosomes 6A, 6D, and 7D. Stem rust severity and reaction type mapped to chromosomes 6D and/or 6A. The Lr34/Yr18/Sr57 gene derived from Kariega on chromosome 7D affected the rust response on flag leaves but not on stems of greenhouse-grown plants. This study showed that phenotyping and genetic analysis of especially major effect stem rust resistance in adult wheat plants is possible and reproducible under controlled conditions in a greenhouse.

Phenotyping of wheat stripe rust in genetic studies has traditionally relied on quantifying disease by means of the modified Cobb Scale. This approach requires scoring of disease severity and response type, either on flag leaves or on a whole plot basis. The use of spectral crop sensors in wheat phenotyping has raised the question of whether this objective methodology is suitable for detecting stripe rust resistance loci in genetic studies. An Avocet S X Francolin#1 recombinant inbred population developed at the International Maize and Wheat Improvement Center (Centro Internacional de Mejoramiento de Maiz y Trigo—acronym CIMMYT), and a Kariega X Avocet S doubled haploid population developed in South Africa, both with available genetic maps, were used in this study. Field trials for stripe rust evaluation of these populations were planted at Greytown, South Africa in 2013 and 2014. Severe and uniformly distributed infection of Puccinia striiformis race 6E22A+ occurred in both years. Populations and parents were phenotyped according to the modified Cobb Scale and with a handheld Trimble GreenSeeker® crop sensor (model HCS-100). The sensing device emits red and infrared light and measures the reflectance of each wavelength in terms of the normalized difference vegetation index (NDVI). In both years, NDVI detected four previously characterized quantitative trait loci (QTL) on chromosomes 1BL, 2BS, 3BS and 6AL in the Avocet S X Francolin#1 population. The same QTL were detected with visual estimates in 2013 but only 2BS was significant in 2014. In the Kariega X Avocet S population, all stripe rust traits, including NDVI, mapped to previously described QTL on chromosomes 2BS, 4AL and 7DS. Remote sensing of infection levels thus consistently detected the same QTL regions as described by using visual ratings in earlier studies, indicating that a crop sensor can be easily applied in genetic mapping of stripe rust resistance in wheat.

Crown rust, caused by Puccinia coronata Corda var. avenae f. sp. avenae (Urban & Markova) (Pca), can negatively impact oat (Avena sativa L.) production in South Africa and little is known about pathogenic variability and cultivar response. Pca infected leaves were obtained from oat trial plots, commercial fields and wild oat (Avena spp.) during the 2016 and 2017 growing seasons for race analysis. Uncharacterised collections from 1998 to 2005 were also included. Single pustule isolates were derived from field collections and used for race typing on 16 international differential lines. Six races were identified from 88 isolates pathotyped with race JBLL originating from wild oat samples, SGLL, SQPL and SSTL from commercial oat samples and SBLL+ from both wild and commercial oat samples. Isolates collected in 1998 typed as races SBLL and SBLL+ and the 2005 isolates as race SQPL. Race SBLL was not detected in the 2016 and 2017 samples with SBLL+ being dominant during 2016–17. This is the first report of South African races with virulence for the resistance genes Pc38, Pc58 and Pc59. Seedling infection types of 70 additional oat lines and cultivars to the described races showed incompatible phenotypes for 27 entries. Field data revealed moderate to high levels of adult plant resistance for a few cultivars to races SBLL+ and SSTL. Genetic analysis of 31 isolates, including two USA control isolates, revealed three genetic lineages. No apparent correlation was observed among year of collection, geographic origin, phenotype and genotype of isolates except for race JBLL that originated from wild oat collections in the Western Cape.

Asian soybean rust was first reported on soybean in South Africa (SA) in 2001 (3). The disease has occurred in all ensuing seasons, particularly in the humid, eastern production regions, causing significant losses in soybean fields not protected by fungicides. In April 2005, rust-infected Pueraria lobata (kudzu) was detected near Nelspruit, Mpumalanga, SA. At this location (25°20′41″S, 30°43′30″E), kudzu plants occurred abundantly on road sides, edges of pine plantations, and in natural vegetation. Most vines were infected, with abaxial surfaces of older leaves often showing 100% severity. Following inoculation with rust spores collected from kudzu, soybean line PI200492 (Rpp1) produced tan lesions typical of a susceptible reaction for Asian soybean rust. PI230970 (Rpp2), PI462312 (Rpp3), and PI459025 (Rpp4) showed red-brown lesions typical of a resistant reaction. Using Ppm1/Ppa2 and Ppm1/Ppm2 primer combinations, the amplification profiles of the internal transcribed spacer region (1) of rust DNA extracted from primary leaves of line PI200492 infected with spores collected from kudzu positively identified the pathogen as Phakopsora pachyrhizi. The Ppm1/Pme2 primer combination specific for P. meibomiae (1) did not yield an amplification product. The Qualiplate ELISA test kit (EnviroLogix Inc., Portland, ME) verified the identification of P. pachyrhizi on an original kudzu sample as well as the leaf material used for DNA analysis. A survey of kudzu at the Nelspruit site during July 2005 confirmed the presence of the pathogen during the offseason for soybean. At that time, incidence of kudzu rust remained high, but few leaves showed high severity. The susceptibility of kudzu to Asian soybean rust has been reported in controlled infection studies in SA (2). To our knowledge, this is the first report of P. pachyrhizi causing rust on a large, naturally occurring kudzu population in SA. References: (1) R. D. Frederick et al. Phytopathology 92:217, 2002. (2) A. Nunkumar. M.Sc. thesis. University of KwaZulu-Natal, South Africa, 2006. (3) Z. A. Pretorius et al. Plant Dis. 85:1288, 2001.

The wheat leaf rust resistance gene Lr32 was transferred from Aegilops tauschii Coss. to bread wheat (Triticum aestivum L.) (1). Despite virulence for Lr32 in some isolates from Bulgaria, Israel, and Turkey, the gene has been reported to be effective in Australia, Mexico, the United States, and South Africa (1,2). A leaf rust isolate that differed in its avirulence/virulence profile from previously recorded races of Puccinia triticina Eriks. in South Africa was collected from triticale (× Triticosecale) in the Western Cape in 2005. According to the South African leaf rust differential set (3), this isolate (UVPt19) was avirulent for Lr3a, 3bg, 3ka, 10, 11, 16, 20, 26, and 30 and virulent for Lr1, 2a, 2b, 2c, 14a, 15, 17, 24, and Thatcher (Tc, control). Except for Lr20 in cv. Thew, all differentials are Tc near-isogenic lines. In comparison with known South African races (3), it differed from race 3SA132 at the Lr10 locus. Using standard rust pathology protocols (3), an expanded set of Lr gene lines (non Tc lines indicated) showed that UVPt19 is avirulent on wheat seedlings containing Lr9, 19, 21, 25, 27+31 (Gatcher), 29, 36 (ER84018), 37, 41 (KS91WGRC10), 44, 45, 47 (KS90H450), 50 (KS96WGRC36), 51 (R05), and 52, and virulent for Lr12, 22a, 23, 28, 32, 33, and 35. In the seedling stage, UVPt19 was virulent for the temperature sensitive genes Lr13, 18, and 34 at 25°C, but produced lower infection types (ITs) on Lr18 and 34 at 14 to 18°C. Seedlings of Pavon 76 (Lr46) were resistant (IT ;1=) to UVPt19. The susceptible response of lines carrying Lr32 was confirmed by high ITs (3++4) on RL5713/2*Mq, RL6086 (TcLr32), and RL5713/2*Mq//6*Palmiet. A control isolate (UVPt9) produced ITs ;1+, ;1+, and ;;1= on these lines, respectively. UVPt19 was virulent on line RL6092 (TcLr20) but avirulent on Thew. When tested on adult plants of lines RL6011 (TcLr12), CT263 (TcLr13), RL6044 (TcLr22a), RL6058 (TcLr34), RL6082 (TcLr35), RL6081 (TcLr37), and Tc (control), UVPt19 was only virulent (IT 3+) on CT263 and Tc. Flag leaves of RL6011 (IT ;1), RL6044 (IT 1), RL6058 (IT Z3-), RL6082 (IT 0;), and RL6081 (IT ;1) were resistant. UVPt19 was virulent on seedlings of 11 of 13 triticale cultivars and lines tested as opposed to UVPt9, which was virulent to only one entry. From a collection of 105 South African bread wheat cultivars and elite breeding lines, UVPt19 was virulent on 13 and five were mixed in their response to this isolate. All IT experiments were repeated. Although virulence has emerged for Lr32 in South Africa, the gene has not been used in local cultivars. Previously, McIntosh et al. (1) also reported that Lr32 has not been exploited in wheat production. On the basis of current evidence, UVPt19 appears to be potentially more damaging to triticale than bread wheat. Furthermore, the race seems rare because it was not collected in a recent wheat leaf rust survey in South Africa (3). References: (1) R. A. McIntosh et al. The Wheat Rusts: An Atlas of Resistance Genes, CSIRO-Kluwer, Dordrecht, the Netherlands, 1995. (2) Z. A. Pretorius. Phytophylactica 21:195, 1989. (3) T. Tarekegn et al. S. Afr. J. Plant Soil 26:51, 2009.

Seven races have been described in the Ug99 race group of Puccinia graminis f. sp. tritici (2). Ug99-related races previously recorded in South Africa are TTKSF, TTKSP, and PTKST (4). In December 2010, severe stem rust infection of the winter wheat cv. Matlabas was observed for the first time in South Africa. Race analysis using the 20 North American (NA) stem rust differential lines and letter code system classified the race as TTKSF. In comparative infection studies in a greenhouse, cv. Matlabas seedlings were susceptible (infection type [IT] 4) to isolate UVPgt61/1 (TTKSF+) collected from Afrikaskop in the eastern Free State, whereas the cultivar was resistant (IT 1 to 2) to stem rust isolates 2013 (TTKSF), UVPgt55 (TTKSF), UVPgt59 (TTKSP), and UVPgt60 (PTKST). Isolate 2013 represents the original collection of race TTKSF in South Africa (1). In addition to the NA differentials, no variation in the IT range of seedlings of lines with Sr7a, 8b, 12, 13, 14, 16, 18, 19, 22, 25, 26, 27, 28, 29, 32, 33, 34, 35, 39, 41, 42, 43, 44, Em, R, Tt2, and Satu was observed between UVPgt61/1 and UVPgt55. With the exception of cv. Matlabas, ITs of 106 South African cultivars likewise did not differentiate UVPgt61/1 and UVPgt55. Seedling IT studies were conducted at least twice. Microsatellite analysis (4) showed that all single pustule isolates established from the original Matlabas isolate formed part of the Ug99 group. When characterized with selected single nucleotide polymorphisms (SNPs), all single pustule isolates shared an identical genotype that differed from UVPgt55 (TTKSF), a foreign introduction into South Africa (1,3). SNP genotype analysis suggests that UVPgt61/1 is genetically dissimilar to UVPgt55, as is Zim1009, another TTKSF+ isolate that was collected from Birchenough in Zimbabwe. Studies are underway to determine the identity of the defeated Sr gene in Matlabas and the cultivar has been added to the South African stem rust differential set. TTKSF+ is the eighth race detected in the Ug99 group. Since no other cultivars or advanced lines were found to carry the Matlabas gene, it is unlikely that race TTKSF+ will threaten wheat production in South Africa. However, the occurrence of a new Ug99-related race emphasizes the variability within this internationally important group. References: (1) W. H. P. Boshoff et al. Plant Dis. 86:922, 2002. (2) R. F. Park et al. Euphytica 179:109, 2011. (3) B. Visser et al. Mol. Plant Pathol. 10:213, 2009. (4) B. Visser et al. Euphytica 179:119, 2011.

Triticale (×Triticosecale), an amphiploid of wheat (mainly Triticum turgidum) and cereal rye (Secale cereale), is an excellent source of resistance to wheat stem rust, caused by Puccinia graminis f. sp. tritici. A collection of 567 triticale accessions originating from 21 countries was evaluated at the seedling stage for reaction to races of P. graminis f. sp. tritici with broad virulence, including TTKSK, TRTTF, and TTTTF. A high frequency (78.4%) of accessions was resistant to race TTKSK, with low infection types ranging from 0; to X. A selection of 353 TTKSK-resistant accessions was evaluated for reaction to three South African isolates of P. graminis f. sp. tritici with single and/or combined virulences to stem rust resistance genes SrSatu, Sr27, and SrKw present in triticale. Genes SrSatu, Sr27, and SrKw were postulated to be present in 141 accessions and contributed to TTKSK resistance. The remaining 212 resistant accessions may possess uncharacterized genes or combinations of known genes that could not be determined with these isolates. These accessions were further evaluated for resistance to races TTKST, TPMKC, RKQQC, RCRSC, QTHJC, QCCSM, and MCCFC. Resistance remained effective across the entire set of races in the majority of the accessions (n = 200), suggesting that the resistances are effective against a broad spectrum of virulence. In all, 129 (79.6%) resistant accessions with noncharacterized genes were resistant to moderately resistant in field stem rust nurseries at Debre Zeit (Ethiopia) and St. Paul (Minnesota). Results from evaluating F2 populations derived from resistant–susceptible crosses revealed that resistance to TTKSK in triticale was conferred mostly by single genes with dominant effects.

Wheat breeders worldwide are seeking new sources of resistance to Puccinia graminis f. sp. tritici race TTKSK. To prioritize field-resistant landraces for follow-up genetic studies to test for the presence of new resistance genes, seedling response to P. graminis f. sp. tritici race TTKSK, molecular markers linked to specific Sr genes, segregation ratios among progeny from crosses, and bulked segregant analyses (BSA) were used. In total, 33 spring wheat landraces with seedling resistance to P. graminis f. sp. tritici race TTKSK were crossed to a susceptible genotype, LMPG-6. The segregation ratios of stem rust reactions in F2 seedlings fit a single dominant gene model in 31 populations and progeny from two crosses gave ambiguous results. Using the 90K wheat single-nucleotide polymorphism genotyping platform, BSA showed that the seedling resistance in 29 accessions is probably controlled by loci on chromosome 2BL. For the three remaining accessions, BSA revealed that the seedling resistance is most likely controlled by previously unreported genes. For confirmation, two populations were advanced to the F2:3 and screened against P. graminis f. sp. tritici race TTKSK. Segregation of the F2:3 families fit a 1:2:1 ratio for a single dominant gene. Using the F2:3 families, BSA located the TTKSK locus on chromosome 6DS to the same location as Sr42.

International audience; Many plant pathogenic fungi have a global distribution across diverse ecological zones and agricultural production systems. Puccinia triticina, the wheat leaf rust fungus, is a major pathogen in many wheat production areas of the world. The objective of this research was to determine the genetic relatedness of P. triticina in different worldwide regions. A total of 831 single-uredinial isolates collected from 11 regions were characterized for multilocus genotype at 23 simple sequence repeat loci and for virulence to 20 lines of wheat with single genes for leaf rust resistance. A total of 424 multilocus genotypes and 497 virulence phenotypes were found. All populations had high heterozygosity and significant correlation between virulence and molecular variation, which indicated clonal reproduction. The populations from North America and South America, Central Asia and Russia, and the Middle East and Europe were closely related for multilocus genotypes and many individual isolates from other continental regions were closely related. Twenty-seven multilocus genotypes were found in more than one continental region, and 13 of these had isolates with identical virulence phenotypes. The wide geographic distribution of identical and highly related multilocus genotypes of P. triticina indicated past and more recent migration events facilitated by the spread of clonally produced urediniospores.

Volatile organic compounds emitted from plant tissues have been implicated to play many roles. Interplant signalling is an experimentally proven phenomenon whereby volatiles produced under stress conditions may diffuse to neighbouring plants to induce a response. The current project was undertaken to investigate a putative signalling event between leaf rust (Puccinia triticina Erikss.) infected and uninfected wheat (Triticum aestivum L.) using a continual air-flow system. Exposure to volatiles emitted by either infected resistant or susceptible plants decreased the percentage leaf area infected and pustule size in recipient plants after a subsequent infection with leaf rust, but in the case of infected resistant plants, the decrease in percentage leaf area infected was significant. The activation of a defence response was confirmed through a significant induction of β-1,3-glucanase activity at 8 h post volatile exposure in exposed resistant and susceptible seedlings, depending on the source of the volatiles. Increased PR1 gene expression supported the activation of the defence response. Emitted volatiles were captured by solid phase micro-extraction and identified by GC-MS. Based on their detection and the literature, ocimene from infected resistant seedlings and green leaf volatiles from infected susceptible seedlings are suggested as likely candidates for the inter-plant communication.

To identify races of Puccinia triticina in southern Africa, samples of infected wheat leaves obtained from Zimbabwe, Zambia and Malawi were analysed at the University of the Free State, Bloemfontein and the Agricultural Research Council-Small Grain Institute, Bethlehem, South Africa (SA). Four races were identified from 63 isolates obtained during 2011–2013. Using the North American notation, these races coded to MCDS (74.6 %), TCPS (12.7 %), FBPT (6.3 %) and SCDS (6.3 %). MCDS and TCPS occurred in both Zimbabwe and Zambia whereas FBPT and SCDS were only detected in Zimbabwe and Malawi, respectively. Three of these races (MCDS, FPBT and SCDS) are also known in SA. SSR analysis of races detected in southern Africa suggested that MCDS and FPBT are more closely related to CCPS (3SA45), a race identified in SA in 2009. Occurrence of similar races across southern Africa indicates migration of inoculum between countries, and highlights the need for each country to monitor and share information on virulence changes in the region. In seedling tests, over 72 % of Zimbabwean commercial cultivars were susceptible to race TCPS which occurred in both Zimbabwe and Zambia. To predict occurrence of adult plant resistance (APR) in these cultivars, they were tested for the presence of gene Lr34 which confers durable resistance to multiple fungal pathogens. Only three cultivars were positive for this gene suggesting that most of the current Zimbabwean commercial cultivars may be susceptible to leaf rust both as seedlings and adult plants, assuming the absence of other APR genes. Three cultivars and 15 breeding lines, all highly resistant as seedlings across races, carried Lr19. One line contained Lr19 and Lr34. It is suggested that sources of race non-specific resistance genes be included in wheat breeding programs in Zimbabwe.

Three major quantitative trait loci (QTL) contribute to the durable adult plant stripe rust resistance in the high-quality bread wheat cultivar Kariega; QYr.sgi-2B.1 and QYr.sgi-4A.1, and the pleiotropic resistance gene Lr34/Yr18/Sr57. While marker-assisted selection is currently being used to incorporate the Kariega stripe rust adult plant resistance into new South African wheat breeding lines, effective selection of the large QTL intervals remains a challenging task. In this study, we describe the development of expressed sequence tag (EST)-derived markers as an effective strategy for increasing the marker density in the selected QTL intervals and the conversion of Diversity Arrays Technology (DArT) and EST-derived markers to sequence tagged site (STS) markers to enable high-throughput screening. To reduce the QTL intervals, a high-resolution mapping population was developed, consisting of 1,020 F2 individuals, from the cross Kariega × Avocet S. Through recombinant selection, QYr.sgi-2B.1 was shown to reside within a 6.1 cM interval on the short arm of chromosome 2B, between marker loci Xbarc55 and Xwmc344, a reduction from the previous interval size of 23 cM. Previously, QYr.sgi-4A.1 was poorly defined, but by mapping selected recombinants for the QYr.sgi-4A.1 interval, the QTL region was narrowed to a 16.3-cM interval between marker loci Xbarc78, Xwmc313 and Xwmc219 on the long arm of chromosome 4A. An EST-STS marker, Xufs1-4A, was also developed for QYr.sgi-4A.1, which improved selection for this slow-rusting QTL. The EST marker strategy was useful in increasing marker density and contributed to improved selection for the Kariega QTL in resistance breeding. In addition, BC4F2 families were developed to study the expression of QYr.sgi-2B.1 and QYr.sgi-4A.1 individually, and in combination with Lr34/Yr18/Sr57 in the common, stripe rust susceptible background of Avocet S.

Samples of wheat and triticale infected with leaf rust were collected from 2008 to 2010 in South Africa to identify Puccinia triticina races. Races were identified based on their virulence profile on standard differential lines. Eight races were identified from 362 isolates. The dominant races were 3SA133 (syn. PDRS) in 2008 (78 %) and 2009 (34 %), and 3SA145 (47 %) in 2010. Race 3SA145 (CCPS) identified in 2009 was a new race in South Africa with virulence for the adult plant resistance gene Lr37. Another new race, 3SA146 (MCDS), was identified in 2010. Race 3SA146 is also virulent for Lr37 but unlike 3SA145, it is virulent for Lr1 and Lr23 and avirulent for Lr3ka and Lr30. Microsatellite analysis showed that 3SA145 and 3SA146 shared 70 % genetic similarity with each other, but only 30 % similarity with other races in South Africa, suggesting that both represent foreign introductions. In seedling tests of 98 South African winter and spring cultivars and advanced breeding lines, 27 % were susceptible to 3SA145 and 3SA146 but resistant to 3SA133. In greenhouse studies of 59 spring wheat adult plants, 19 % of breeding lines and 46 % of cultivars were susceptible to 3SA145, whereas 29 % of the lines and 53 % of cultivars were susceptible to 3SA146. The cssfr6 gene-specific DNA marker confirmed the presence of Lr34 gene for leaf rust resistance in a homozygous condition in 28 wheat entries. Five entries were heterogeneous for Lr34. Several entries which were susceptible as seedlings to the new races carried Lr34. These lines are expected to show lower levels of leaf rust as adult plants. Results of these studies indicate a continued vulnerability of South African wheat cultivars to new races and emphasise the importance of regular rust monitoring and the need to incorporate genes for durable resistance.

A gene for Ug99 resistance from wheat landrace CItr 4311 was detected on the long arm of chromosome 2B. Wheat landrace CItr 4311 has seedling resistance to stem rust caused by Puccinia graminis f. sp. tritici race TTKSK and field resistance to the Ug99 race group. Parents, F1 seedlings, 121 doubled haploid (DH) lines, and 124 recombinant inbred lines (RILs) developed from a cross between CItr 4311 and the susceptible line LMPG-6 were evaluated for seedling resistance to race TTKSK. Goodness-of-fit tests indicated that a single dominant gene in CItr 4311 conditioned the TTKSK resistance. The 90 K wheat iSelect SNP platform was used to genotype parents and the DH population. The seedling resistance locus was mapped to the chromosome arm 2BL. Parents and the DH population were evaluated for field resistance in Kenya. One major QTL for the field resistance was consistently detected in the same region on 2BL as the seedling resistance. Using KASP assays, five linked SNP markers were used to verify the result in the 124 RIL, 35 wheat accessions, 46 DH lines from the LMPG-6/PI 165194 cross and F1 seedlings, and susceptible bulks derived from crosses between six resistant landraces with LMPG-6. Race specificity, mapping results, and haplotype similarity with lines with Sr9h (Gabo 56, Timstein, and PI 670015), support the hypothesis that the Sr gene in CItr 4311 and the landraces is Sr9h. The KASP assays developed in this study will be useful for pyramiding the TTKSK resistance from CItr 4311 with other Sr genes effective against Ug99.

Characterising resistance at different levels of expression is important in understanding host defence mechanisms and the improvement of durable disease resistance in crop plants. Histological reactions of the lentil cultivars EL-142 (susceptible) and Gudo (resistant) to infection by Uromyces viciae-fabae, were investigated by means of fluorescence and confocal laser microscopy. Components of resistance included the proportion of successful penetrations, early abortion, host cell necrosis and colony size. The percentage of germinated urediniospores that had not penetrated was significantly higher for Gudo than for EL-142. Furthermore, Gudo had a higher percentage of early aborted colonies, frequently associated with host cell necrosis, than the susceptible cultivar. The host cell necrosis index for Gudo was 1.13, indicating an excessive hypersensitive response to lentil rust. At the macroscopic level, rust pustules on Gudo were surrounded by chlorotic and necrotic flecks. Results indicated that the resistance to lentil rust in Gudo is the result of prehaustorial and posthaustorial mechanisms. However, resistance to rust may not be durable because of its hypersensitive nature.

Following the appearance of stripe rust in South Africa in 1996, efforts have been made to identify new sources of durable resistance. The French cultivar Cappelle-Desprez has long been considered a source of durable, adult plant resistance (APR) to stripe rust. As Cappelle-Desprez contains the seedling resistance genes Yr3a and Yr4a, wheat lines were developed from which Yr3a and Yr4a had been removed, while selecting for Cappelle-Desprez derived APR effective against South African pathotypes of the stripe rust fungus, Puccinia striiformis f. sp. tritici. Line Yr16DH70, adapted to South African wheat growing conditions, was selected and crossed to the stripe rust susceptible cultivar Palmiet to develop a segregating recombinant inbred line mapping population. A major effect QTL, QYr.ufs-2A was identified on the short arm of chromosome 2A derived from Cappelle-Desprez, along with three QTL of smaller effect, QYr.ufs-2D, QYr.ufs-5B and QYr.ufs-6D. QYr.ufs-2D was located within a region on the short arm of chromosome 2D believed to be the location of the stripe rust resistance gene Yr16. An additional minor effect QTL, QYr.ufs-4B, was identified in the cv. Palmiet. An examination of individual RILs carrying single or combinations of each QTL indicated significant resistance effects when QYr.ufs-2A was combined with the three minor QTL from Cappelle-Desprez, and between QYr.ufs-2D and QYr.ufs-5B.

The appearance and spread of races of Puccinia graminis f. sp. tritici with virulence for the Sr31 resistance gene has renewed interest in breeding for durable resistance to stem rust of wheat. Since the occurrence of stem rust has been low in South Africa until the detection of race TTKSF in 2000, breeding for resistance to this disease has not been a primary objective. The aim of this study was to test bread wheat cultivars and lines at the seedling stage for their infection response to stem rust, thus determining their level of resistance or vulnerability. A collection of 65 bread wheat entries was tested with one USA race, two Eastern African races, and three South African races of P. graminis f. sp. tritici. The Eastern African and South African races all belong to the Ug99 lineage. The cultivars Duzi, Caledon, Elands, PAN 3364, PAN 3191, SST 047, SST 399, and Steenbras produced resistant infection types (IT < 3) to all races. The molecular marker Sr24#50 indicated the presence of Sr24 in 12 entries. In cultivars resistant to TTTTF, TTKSF, and TTKSP but susceptible to TTKSK and PTKST, the iag95 DNA marker indicated the presence of Sr31 in five wheat lines. Using the cleaved amplified polymorphic sequence marker csSr2, Sr2 was detected in PAN 3377, Inia, and Steenbras. Few South African wheat cultivars appear to have a broad-based resistance to stem rust, as 88% of the entries were susceptible as seedlings to at least one of the races tested. Diversification of resistance sources and more directed breeding for stem rust resistance are needed in South Africa.

Activities of potential reactive oxygen species generating enzymes and the subsequent production of H2O2, were investigated during the rust (Puccinia helianthi)—sunflower interaction using resistant (PhRR3) and susceptible (S37–388) lines. The resistance response was associated with induced activities of NADPH oxidase and peroxidase, and resultant high levels of hydrogen peroxide that peaked 9 h after inoculation. This was confirmed by a concomitant induction of superoxide dismutase, an antioxidative enzyme. The induced high levels of reactive oxygen species generating enzyme activities and hydrogen peroxide preceded the development of considerably less disease symptoms in resistant plants, suggesting possible early involvement of reactive oxygen species generation during the resistance response.

The potential to control leaf rust (Puccinia triticina; pathotype UVPt9) in vivo in susceptible (Thatcher) and resistant (Thatcher/Lr15) near-isogenic wheat (Triticum aestivum) lines by foliar applications of crude plant leaf extracts from Tulbaghia violacea and Agapanthus africanus, as well as a commercially available natural product, ComCat®, and a Lupinus albus seed suspension (SS) was investigated. In vitro activities of the PR-proteins, β-1,3-glucanase, chitinase and peroxidase were quantified in these two wheat lines under both non-infected and infected conditions. Although foliar application of the different plant extracts accelerated the activities of all three enzymes in resistant infected wheat plants, it was only the A. africanus extract that increased the in vitro activities of the three apoplastic pathogenesis-related proteins significantly in both susceptible and resistant wheat cultivars, whether uninfected or infected. The latter resulted in the reduction of pustule and necrotic lesion formation in the susceptible and resistant wheat lines, respectively. Foliar treatment of wheat seedlings with either ComCat® or SS had no effect on pustule and necrotic lesion formation. The A. africanus crude extract also had a significant in vitro inhibitory effect on both leaf rust spore germination and subsequent germ tube development.

Adult plant resistance to stripe (yellow) rust in the wheat cultivar Kariega has previously been ascribed to a major quantitative trait locus (QTL) on each of chromosomes 2B and 7D, along with a number of minor QTL. We have extended both the size of the cv. Kariega × cv. Avocet S mapping population, and the marker coverage within it, by assembling a set of Diversity Array Technology (DArT) markers. This has allowed for the analysis of the genetic basis of the adult plant and seedling resistances to stripe, leaf and stem rust present in the two mapping population parents. The stripe rust reactions of the segregating material were assessed in both field (three scoring dates) and greenhouse experiments. The chromosome 2B QTL became more important than the Lr34/Yr18 complex on chromosome 7D as the plants aged. As the infection progressed, the two QTL explained an increasing proportion of the variance for percentage leaf area infected. The cv. Kariega allele at the minor chromosome 4A QTL had a consistent effect on the severity of stripe rust infection and the overall plant reaction at the earlier scoring dates, but lost importance as the disease progressed. Several rust resistances were detected using an improved greenhouse-based test.

The Lr56/Yr38 translocation consists primarily of alien-derived chromatin with only the 6AL telomeric region being of wheat origin. To improve its utility in wheat breeding, an attempt was made to exchange excess Ae. sharonensis chromatin for wheat chromatin through homoeologous crossover in the absence of Ph1. Translocation heterozygotes that lacked Ph1 were test-crossed with Chinese Spring nullisomic 6A tetrasomic 6B and nullisomic 6A-tetrasomic 6D plants and the resistant (hemizygous 6A) progeny were analyzed with four microsatellite markers. Genetic mapping suggested general homoeology between wheat chromosome 6A and the translocation chromosomes, and showed that Lr56 was located near the long arm telomere. Thirty of the 53 recombinants had breakpoints between Lr56 and the most distal marker Xgwm427. These were characterized with additional markers. The data suggested that recombinants #39, 157 and 175 were wheat chromosomes 6A with small intercalary inserts of foreign chromatin containing Lr56 and Yr38, located distally on the long arms. These three recombinants are being incorporated into adapted germplasm. Attempts to identify the single shortest translocation and to develop appropriate markers are being continued.

Yield loss in lentil (Lens culinaris Medik.) due to rust (Uromyces viciae-fabae [Pers.] J. Schrot) was determined by assessing crop and disease parameters at different growth stages and leaf canopy layers in field epidemics at Akaki, Ethiopia. The epidemics were created by inoculation of the rust-susceptible cultivar EL-142 with U. viciae-fabae and spraying plots with tebuconazole at different frequencies. The epidemics produced disease progress curves that varied significantly in the rate (rL ) of temporal progression and area under the disease progress curve (AUDPC). The rust epidemic, in particular between early flowering and early pod formation, had a significant influence on seed yield, pods per plant and seed mass. Mean seed yield losses up to 41.6% were recorded. The number of seeds per pod remained unaffected by the disease. The effect of rust on seed yield of lentil can be predicted with AUDPC and critical-point models using disease severity assessed on the upper canopy layer in the early floweri...

The tendency of unpaired meiotic chromosomes to undergo centric misdivision was exploited to translocate leaf rust and stripe rust resistance genes from an Aegilops kotschyi addition chromosome to a group 2 chromosome of wheat. Monosomic and telosoanic analyses showed that the translocation occurred to wheat chromosome arm 2DL. The introgressed region did not pair with the corresponding wheat 2DL telosome during meiosis suggesting that a whole arm may have been transferred. Female transmission of the resistance was about 55% whereas male transmission was strongly preferential (96%). The symbols Lr54 and Yr37 are proposed to designate the new resistance genes.

Rust in common bean (Phaseolus vulgaris L.) is caused by Uromyces appendiculatus Pers.:Pers. (Unger) which exhibits a high level of pathogenic diversity. Resistance to this disease is conditioned by a considerable number of genes. Pyramiding resistance genes is desirable and could be simplified by the use of molecular markers closely linked to the genes. The resistance gene Ur-13, present in the South African large seeded cultivar Kranskop, has been used extensively in the local breeding program. The purpose of this study was the development of a molecular marker linked to Ur-13. An F(2) population derived from a cross between Kranskop and a susceptible (South African) cultivar Bonus was used in combination with bulked segregant analysis utilizing the amplified fragment length polymorphism (AFLP) technique. Seven AFLP fragments linked significantly to the rust resistance and five were successfully converted to sequence characterized amplified region (SCAR) markers. The co-dominant SCAR markers derived from a 405 bp EAACMACC fragment, KB 126, was located 1.6 cM from the gene. Two additional SCAR markers and one cleaved amplified polymorphic sequence marker were located further from the gene. The gene was mapped to linkage group B8 on the BAT 93/Jalo EEP 558 core map (chromosome 3).

Infection of dry beans (Phaseolus vulgaris L.) by rust, caused by Uromyces appendiculatus Pers.: Pers. (Unger), results in regular yield and quality losses in South Africa. The growing of resistant varieties is generally considered the most cost effective control measure. To meet this objective, rust resistance has been an important selection criterion since the dry bean breeding programme of the Agriculture Research Council (ARC) was initiated at Potchefstroom in the 1970's. The breakdown of resistance in earlier varieties indicated that pathogenic variation occurred in U. appendiculatus in South Africa and that a more coordinated resistance breeding programme, including race surveys, was needed. This article describes the approach that was followed at the ARC and reviews progress made with germplasm improvement by means of backcrossing. Rust resistance has been transferred from 16 donor lines, including the genes Ur-3+, Ur-5, Ur-11 and uncharacterized genes, to adapted germplasm. Results from field test...

An inoculation technique resulting in uniform spore deposition for obtaining reproducible and accurate data on host responses is required for quantitative studies of resistance expression. The feasibility of obtaining uniform spore deposition on Lens culinaris, a plant with compound leaves, was investigated using a settling tower. Uniformity of spore deposition on adhesive coated glass slides was assessed by dispersing 1,2,4 and 8 mg spores of Uromyces viciae-fabae, the causal agent of lentil rust, into the tower. When an 8 mg spore quantity was discharged the number of spores deposited per square centimetre did not vary significantly (P > 0.05) between the different locations of the glass slides on the target area. A linear, relation was found between mass of spores discharged into the tower and spores deposited. Counts for 1, 2, 4 and 8 mg were, respectively, 82, 244, 384 and 972 spores per square centimetre. Uniformity of spore deposition increased as the amount discharged increased, and the coefficien...

Langdon durum D-genome disomic substitution lines were used to study the chromosome locations of adult-plant leaf rust resistance genes identified from tetraploid wheat accessions. The accessions are 104 (Triticum turgidum subsp. dicoccum var. arras) and 127 (T. turgidum subsp. durum var. aestivum). The complete sets of the substitution lines were crossed as female parents with the accessions and F1 double monosomic individuals selected at metaphase I. Segregating F2 individuals were inoculated during the flag leaf stage with pathotype UVPrt2 of Puccinia triticina. The substitution analysis involving accession 104 showed that the gene for leaf rust resistance is located on chromosome 6B. The analysis with accession 127 indicated that chromosome 4A carries a gene for leaf rust resistance. The two novel genes are temporarily designated as Lrac104 and Lrac127, respectively from accessions 104 and 127.

Linked leaf rust and stripe rust resistance genes introduced from Triticum dicoccoides protected common wheat seedlings against a range of pathotypes of the respective pathogens. The genes were chromosomally mapped using monosomic and telosomic analyses, C-banding and RFLPs. The data indicated that an introgressed region is located on wheat chromosome arm 6BS. The introgressed region did not pair with the ‘Chinese Spring’ 6BS arm during meiosis possibly as a result of reduced homology, but appeared to pair with 6BS of W84-17 (57% of pollen mother cells) and ‘Avocet S’. The introgressed region had a very strong preferential pollen transmission (0.96–0.98) whereas its transmission through egg cells (0.41–0.66) varied with the genetic background of the heterozygote. Homozygous resistant plants had a normal phenotype, were fertile and produced plump seeds. Symbols Lr53 and Yr35 are proposed to designate the respective genes.

For accurate lentil (Lens culinaris) rust phenotyping in controlled environments, conditions for infection should be optimized. Therefore, the effects of temperature on germination and germ tube growth of Uromyces viciae-fabae, as well as the effect of different dew periods, were quantified. In all experiments urediniospores of a single-pustule isolate were applied using a previously calibrated settling tower. After 3 h of incubation, a high percentage (‡80%) of spore germination was observed on 1.5% water agar at 10, 15, 20 and 25� C, with an optimum (99%) at 20� C. At this sampling time the length of germ tubes ranged from 66 lm (10� C) to 196 lm (20� C). Growth of germ tubes increased progressively from 10 to 20� C and then declined at 25� C. For minimum infection of lentil cultivar EL-142 at 20� C, a dew period of at least 3 h was required, whereas maximum infection occurred with a dew period of 24 h. Infection efficiency increased linearly as the duration of dew period increased from 0 to 24 h. Regression models that best described the quantitative relationship between the environmental variables and growth of the pathogen and development of rust were derived empirically. Such models are of significance in optimizing studies of the particular pathosystem as well as eventual lentil rust prediction models.

A doubled haploid wheat population of 150 lines was constructed from the F1 of a cross between cultivars Kariega and Avocet S using the wheat-maize technique. Segregation and linkage analysis of 203 DNA markers, two storage protein markers and the stem rust resistance gene Sr26 yielded 31 linkage groups of which 28 were chromosome-anchored. These linkage groups covered the entire genome of 21 chromosomes. SSR markers were advantageous for chromosome anchoring and AFLP markers for consolidation of the various linkage groups. A significant feature of the linkage map is a relatively low level of polymorphism for markers on the D genome, viz, 18.5% of all markers mapped. The Kariega × Avocet S doubled haploid population and linkage maps have emerged as valuable resources for further genetic studies of qualitative and quantitative traits of economic importance in bread wheat.

Three hundred and fifty three Triticum accessions, several also classified as Aegilops and comprising 13 diploid, tetraploid or hexaploid species, were screened for seedling and adult-plant resistance to Puccinia triticina Eriks. using a mixture of pathotypes UVPrt2, 3, 9 and 13. Seedlings were spray-inoculated with a suspension of freshly collected urediospores in distilled water containing Tween 20® seven days after planting. Infection types (ITs) were scored 10 days post-inoculation (d.p.i.). Fully expanded flag leaves were inoculated and ITs and leaf rust severity were scored 16 d.p.i. One hundred and eighty two of the accessions were resistant to moderately resistant in the adult stage, whereas 126 were resistant or moderately resistant as seedlings to the pathotype mixture. Hypersensitive adult-plant resistance was particularly apparent in lines of T. timopheevii, T. sharonense, T. longissimum, T. searsii and T. turgidum. In T. turgidum, which comprised 272 accessions, approximately 44% of the adult plants were resistant to moderately resistant compared to 28% of the seedlings. The expression of these adult-plant resistances varied between hypersensitive flecking of flag leaves, and small pustules commonly associated with chlorosis and/or necrosis of leaf tissue. Partial resistance, expressed by small pustules without any apparent chlorosis, was observed in species such as T. tauschii, T. turgidum ssp. durum and T. turgidum ssp. pyramidale.

The life-cycle of Puccinia sorghi, a heteroecious fungus, consists of five well-defined spore stages. The uredinial and telial stages are completed on the primary maize host whereas pycnial and aecial stages occur on Oxalis comiculata (creeping sorrel), a perennial and widespread weed. Although the sexual phase of maize rust has been known to occur in South Africa for many years, accurate descriptions of spore stages are not readily available. Surface-sterilised discs of maize leaves containing telia were placed on water agar plates and inverted over O. comiculata plants covered with a settling tower. Removal of plants at different time intervals showed that 6 h of high humidity at 19–21°C were sufficient for germination of teliospores and infection of the alternate host by basidiospores. Both light and scanning electron microscopy of O corniculata leaf sections provided detailed descriptions of the pycnia, containing receptive hyphae and spermatia. and aecia with aeciospores. The frequent detection of ae...

The inheritance of resistance to race RSA-Ua7 of the rust pathogen Uromyces appendiculatus in the South African dry bean (Phaseolus vulgaris) cultivar Kranskop, as well as the relationship of rust resistance between Kranskop and the international rust differential cultivars Redlands Pioneer and PC-50, were determined. Segregation of progeny from a Bonus x Kranskop cross, and the backcross to Bonus, indicated that rust resistance in Kranskop is conditioned by a single dominant gene. It is proposed that this gene be named Ur-13, according to standard protocol. No segregation occurred in the F1 and F2 plants of a Redlands Pioneer x Kranskop cross and its reciprocal, implying that resistance to race RSA-Ua7 is conditioned by the same gene in Kranskop and Redlands Pioneer. Segregation of progeny from both the PC-50 x Kranskop and Kranskop x PC-50 crosses indicated the presence of two independent genes, with an additive effect to race RSA-Ua7.

Sclerotium rolfsii Sacc. causes disease of numerous crop plants worldwide, including groundnuts. Control of this pathogen is difficult as it produces sclerotia which overwinter in the soil to emerge as inoculum and cause disease the following season. Various chemical, biological and cultural control strategies have been suggested and implemented, some of which have reduced disease incidence in the field. No studies have yet been undertaken in South Africa to control this disease on groundnut, either chemically, biologically or by cultural practices. In this study, several strategies were investigated for the control of S. rolfsii on groundnuts. Difenoconazole was identified as a fungicide that could possibly be applied in combination with Trichoderma harzianum, a biological antagonist of S. rolfsii, above carbendazim and flusilazole, and chlorothalonil. Difenoconazole significantly reduced the growth rate of S. rolfsii but not of T. harzianum. The cultivation of infected fields with an inversion plough significantly reduced infection of groundnuts by S. rolfsii and also improved the quality of the produce, while yield was not increased. Lower plant density increased the incidence of disease in an infected field, and is therefore not considered to be a viable form of cultural control.

A programme aiming to transfer leaf rust resistance genes identified in a collection of wild Triticum species was initiated in 1993. In 2000, 25 promising backcross populations were available, 19 of which bred true for resistance. Seedlings of the above lines were tested with nine leaf rust, four stem rust and two stripe rust pathotypes endemic to South Africa. A subset of five lines in which resistance (derived from T. dicoccoides, T. sharonense, T. speltoides and T. peregrinum) appeared to be integrated on wheat chromosomes and six addition lines with added chromosomes from T. kotschyi, T. peregrinum, T. umbellulatum, T. macrochaetum and T. neglectum appeared to have wide spectrum resistances, and were retained. In several instances promising stem rust and/or stripe rust resistance genes were co-transferred with leaf rust resistance. The stripe rust resistance was also effective to four Australian pathotypes and appeared to be novel. Temporary gene designations were assigned to the resistance genes in f...

Field trials were conducted from 1997 to 1999, in both the winter and summer rainfall areas of South Africa, to determine the effect of Puccinia striiformis Westend, f. sp. tritici Erikss. on yield and quality of bread wheat (Triticum aestivum L). During 1997 in the south Western Cape, combined seven and flag leaf treatments of five tri- azole fungicides, over three cultivare, resulted in a 43% yield increase. Stripe rust head infections were most effectively controlled by the application of fungicides closely to or just after head emergence. Yield was negatively correlated with the area under the disease progress curve (AUDPC [R2 = 0.23]). In the absence of disease during 1998 fungicide treatments failed to significantly increase yield or hectolitre mass. During 1999 the most effective control of stripe rust was obtained by applying propiconazole at both the seven and flag leaf stages as well as where triticonazole seed-treatment was applied in additjon to the latter treatments. The latter two treatments...

Leaf rust, caused by Puccinia triticina, is considered one of the most important diseases of wheat. In South Africa the genes Lr29, Lr34, Lr35 and Lr37 confer effective resistance to leaf rust, qualifying them for use in cultivar improvement. To study possible secondary effects of these genes, a collection of BC6 lines containing each of the genes singly, was evaluated for breadmaking quality. The recurrent parent Karee, and Thatcher NILs used as resistance donors in the primary crosses, as well as Thatcher, were included as checks. The presence of Lr29, Lr34, Lr35 and Lr37 caused a significant increase in flour protein and water absorption. For most of the other characteristics the NILs performed statistically similar to the recurrent parent. Some sib lines performed significantly better than others, emphasising the value of selecting for improved quality among backcross lines.