South African Wheat Cultivars Research Articles

Endophytic Effect of the South African Beauveria bassiana Strain PPRI 7598 on the Population Growth and Development of the Russian Wheat Aphid, Diuraphis noxia

The Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), is one of the main pests of small-grain cereal crops, including bread wheat, Triticum aestivum (Poaceae). In a series of glasshouse experiments, we evaluated the systemic effect of endophytic Beauveria bassiana strain PPRI 7598 on D. noxia biotype RWASA1 using three South African wheat cultivars, Gariep, Molopo, and Kariega. The objectives of the study were: (a) to determine the effect of endophytism on RWA reproduction and population growth, and (b) to assess the effect of the endophyte on aphid biomass and T. aestivum response to D. noxia herbivory using a damage rating index. Plant endophytic colonisation was confirmed before each trial using a B. bassiana-selective medium. Three independent trials were performed 10 days apart under glasshouse conditions. The effect of the endophyte-treated versus non-treated plants varied significantly in terms of net reproductive rate (R0) and the intrinsic rate of increase (rm) of the D. noxia population. Overall, the endophyte significantly reduced D. noxia R0 by approximately 14 nymphs/female and decreased the aphid mass by 13% in treated plants, whereas the mean aphid mass increased by 17% in control plants in all pooled cultivars. These findings demonstrated the endophytic potential of B. bassiana strain PPRI 7598 for suppression of D. noxia populations in RWASA1-susceptible cultivars. The integration of B. bassiana endophytism with host plant resistance may counteract biotype development and support a more sustainable approach towards RWA control in integrated pest management programmes.

Effect of salinity on the germination of wheat and barley in South Africa

AbstractField crops are most susceptible to salt stress in the early stages of growth. There is a general belief that barley (Hordeum vulgare L.) is more salt‐tolerant than wheat (Triticum aestivum L.), yet little is known regarding the response of different South African wheat and barley cultivars to saline conditions. An experiment was conducted to study the effects of salinity on seed germination in three South African spring wheat cultivars (SST 027, SST 056, and SST 087) and three spring barley cultivars (Nemesia, Erica, and Hessekwa). The experiment was conducted in petri dishes in a growth incubator at a constant temperature of 20 °C for 7 d. Seeds were exposed to five NaCl solutions with electrical conductivity (EC) levels of 4, 8, 12, 16, and 20 dS m−1 and were compared with those exposed to a solution with an EC of 0 dS m−1 (distilled water), which served as a control. The experiment design was a completely randomized design. The study showed that salinity influenced seed germination in all wheat and barley cultivars. Although all cultivars showed a reduction in total germination percentage with increasing salinity from EC levels of 0 to 20 dS m−1, the differences were only significant (P < .05) at high EC levels (16–20 dS m−1). Wheat cultivars outperformed barley cultivars at EC levels of 0, 4, 8, 12, and 16 dS m−1. The study showed that salinity influenced seed germination in both wheat and barley, but barley was less salt‐tolerant during germination than wheat.

Evaluation of Dryland Wheat Cultivars on the Market in South Africa for Resistance against Four Known Russian Wheat Aphid, <i>Diuraphis noxia</i>, Biotypes in South Africa

An increased wheat yield potential under changing environmental conditions is a challenge in agriculture. Resistant wheat lines can yield more than susceptible wheat lines in the presence of Russian wheat aphid infestation. There are currently four Russian wheat aphid (RWA) biotypes known in South Africa with different virulence against different wheat cultivars. To keep up with the ever-changing patterns it is necessary to screen the cultivars for resistance against these Russian wheat aphid (RWA) biotypes. All the dryland wheat cultivars on the market were evaluated for resistance against the four known Russian wheat aphid (RWA) biotypes in South Africa. Through this evaluation, the status of Russian wheat aphid (RWA) resistance in South African dryland wheat cultivars can be updated to adapt to environmental changes and the wheat industry can adapt to changes in virulence of Russian wheat aphid (RWA) biotypes that may cause damage to Russian wheat aphid (RWA) resistant cultivars, subsequently affecting yield. Evaluations were done in the glasshouse by screening wheat cultivars against four different South African Russian wheat aphid (RWA) biotypes, RWASA1-RWASA4, under controlled conditions. The glasshouse evaluations showed that out of the 19 dryland wheat cultivars currently on the market in South Africa 16 are resistant against RWASA1, 7 are resistant against RWASA2, 7 are resistant against RWASA3 and 5 are resistant against RWASA4. Dryland wheat cultivars were also evaluated under field conditions at four different field localities. In the field, 5 cultivars were resistant to RWASA3 at two localities, respectively, and 3 and 5 cultivars were resistant to RWASA4 at two localities, respectively. Since Russian wheat aphid (RWA) damage can influence the final yield of a wheat cultivar significantly, changing conditions can influence both resistant cultivars, and the virulence of Russian wheat aphid (RWA). It is advisable to evaluate wheat cultivars on the market under different conditions and with all known Russian wheat aphid (RWA) biotypes in an area.

Phenotypic and genotypic description of Puccinia graminis f. sp. tritici race 2SA55 in South Africa

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.

New Puccinia triticina races on wheat in South Africa

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.

Targeted Haplotype Comparisons between South African Wheat Cultivars Appear Predictive of Pre-harvest Sprouting Tolerance.

Pre-harvest sprouting (PHS) has been a serious production constraint for over two decades, especially in the summer rainfall wheat production regions of South Africa. It is a complex genetic trait controlled by multiple genes, which are significantly influenced by environmental conditions. This complicates the accurate prediction of a cultivar's stability in terms of PHS tolerance. A number of reports have documented the presence of major QTL on chromosomes 3A and 4A of modern bread wheat cultivars, which confer PHS tolerance. In this study, the SSR marker haplotype combination of chromosomes 3A and 4A of former and current South African cultivars were compared with the aim to select for improved PHS tolerance levels in future cultivars. A total of 101 wheat cultivars, including a susceptible cultivar and five international tolerant sources, were used in this study. These cultivars and donors were evaluated for their PHS tolerance by making use of a rain simulator. In addition, five seeds of each entry were planted out into seedling trays and leaf material harvested for DNA isolation. A modified CTAB extraction method was used before progressing to downstream PCR applications. Eight SSR markers targeted from the well-characterized 3A and 4A QTL regions associated with PHS tolerance, were used to conduct targeted haplotype analysis. Additionally, recently published KASP SNP markers, which identify the casual SNP mutations within the TaPHS1 gene, were used to genotype the germplasm. The haplotype marker data and phenotypic PHS data were compared across all cultivars and different production regions. A relative change in observed phenotypic variation percentage was obtained per marker allele and across marker haplotype combinations when compared to the PHS susceptible cultivar, Tugela-DN. Clear favorable haplotypes, contributing 40–60% of the variation for PHS tolerance, were identified for QTL 3A and 4A. Initial analyses show haplotype data appear to be predictive of PHS tolerance status and germplasm can now be selected to improve PHS tolerance. These haplotype data are the first of its kind for PHS genotyping in South Africa. In future, this can be used as a tool to predict the possible PHS tolerance range of a new cultivar.

The Content of Tocols in South African Wheat; Impact on Nutritional Benefits.

Wheat is a major component within human consumption, and due to the large intake of wheat, it has an impact on human nutritional health. This study aimed at an increased understanding of how the content and composition of tocols may be governed for increased nutritional benefit of wheat consumption. Therefore, ten South African wheat cultivars from three locations were fractionated into white and whole flour, the content and concentration of tocols were evaluated by high performance liquid chromatography (HPLC), and vitamin E activity was determined. The content and composition of tocols and vitamin E activity differed with fractionation, genotype, environment, and their interaction. The highest tocol content (59.8 mg kg−1) was obtained in whole flour for the cultivar Elands grown in Ladybrand, while whole Caledon flour from Clarence resulted in the highest vitamin E activity (16.3 mg kg−1). The lowest vitamin E activity (1.9 mg kg−1) was found in the cultivar C1PAN3118 from Ladybrand. High values of tocotrienols were obtained in whole flour of the cultivars Caledon (30.5 mg kg−1 in Clarens), Elands (35.5 mg kg−1 in Ladybrand), and Limpopo (33.7 mg kg−1 in Bultfontein). The highest tocotrienol to tocopherol ratio was found in white flour (2.83) due to higher reduction of tocotrienols than of tocopherols at fractionation. The quantity and composition of tocols can be governed in wheat flour, primarily by the selection of fractionation method at flour production, but also complemented by selection of genetic material and the growing environment.

Field Screening of Lesotho and South African Wheat Cultivars for Russian Wheat Aphid Resistance

Russian wheat aphid (Diuraphis noxia) is an international wheat pest and was first recorded in South Africa in 1978 in the Bethlehem area in the Eastern Free State. Le-sotho lies adjacent to one of the largest wheat producing areas in South Africa, the Eastern Free State, where winter wheat and facultative types are cultivated under dry land conditions. Wheat (Triticum aestivum L.) is an important crop adapted to all agro-ecological zones of Lesotho. Russian wheat aphid may have a significant impact on wheat yield. No monitoring or pest control is being done in Lesotho and at this stage there is very little information on the Russian wheat aphid resistance of wheat culti-vars cultivated in Lesotho. In view of this it is important to monitor the distribution of Russian wheat aphid biotypes in Lesotho and determine the level of Russian wheat aphid resistance in local Lesotho wheat cultivars. Two local Lesotho wheat cultivars, Bolane and Makalaote were screened together with South African cultivars Elands, Matlabas, Senqu, PAN3379, PAN3118 and SST387, in the glasshouse against all four known biotypes that occur in South Africa. All these cultivars were also planted in 5 m plots in the field at two localities Leribe and Roma in the lowlands of Lesotho. These cultivars were screened in the field for Russian wheat aphid resistance. The predomi-nant Russian wheat aphid biotypes in these areas were also determined. The Lesotho cultivar, Bolane had resistance against RWASA2 in the glasshouse, while Makalaote did not have any Russian wheat aphid resistance in either the glasshouse or field screenings. To contribute to food security an increasing wheat yield potential is a high priority. Russian wheat aphid has been included in the list of important international cereal pests. Russian wheat aphid adapts to changing environments and taking their ecology, distribution, virulence patterns, and variability into account is important in minimizing the gap between actual and attainable yields. Current management prac-tices for winter wheat in South Africa include the use of resistant cultivars, which is the most economical management strategy for Russian wheat aphid. Introducing Russian wheat aphid resistant cultivars in Lesotho will improve overall yield and as a result food security. This will also result in lower Russian wheat aphid pest pressure in the adjacent wheat production areas in the Eastern Free State, South Africa.

Tocochromanol concentration, protein composition and baking quality of white flour of South African wheat cultivars

Vitamin E has antioxidant properties and consists of four tocopherols and four tocotrienols (α, β, γ and δ), collectively called tocochromanols. This study was carried out to determine the tocopherol and tocotrienol concentration in white flour of 10 South African wheat cultivars grown in 3 environments, sourced from 2 breeding programmes α- and β-tocopherols; α- and β-tocotrienols were found in significant concentrations. The concentration of the tocochromanols in the white flour (4.87–11.73mgkg−1) was much lower than that in whole flour of soft wheat (74.3mgkg−1) and durum wheat (60.6mgkg−1). The concentration of tocochromanols was strongly influenced by genotype, the environment and the interaction between the two. Cultivars originating from one breeding programme had a significantly higher concentration (9.12mgkg−1) of tocochromanols than from the other breeding programme (5.28mgkg−1). All of the cultivars had good baking quality characteristics (such as high loaf volume, protein content and wet gluten content). Loaf volume was significantly positively influenced by the sodium dodecyl sulphate (SDS) insoluble small polymeric and small and large monomeric proteins, as well as the SDS soluble large polymeric proteins. White flour could therefore be a complementary source of vitamin E in the diet, and selection for increased tocochromanol concentration can lead to increased nutritional value of bread wheat flour without a penalty to baking quality.

Diversity in Puccinia triticina detected on wheat from 2008 to 2010 and the impact of new races on South African wheat germplasm

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.

Seedling resistance to stem rust race Ug99 and marker analysis for Sr2, Sr24 and Sr31 in South African wheat cultivars and lines

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.

First Report of a Puccinia graminis f. sp. tritici Race Virulent to the Sr24 and Sr31 Wheat Stem Rust Resistance Genes in South Africa.

Isolates of Puccinia graminis f. sp. tritici belonging to the Ug99 race group are virulent to a broad spectrum of resistance genes, rendering most of the world's wheat germplasm susceptible to stem rust (3). Following the initial detection of Ug99 (TTKSK, North American [NA] race notation) in Uganda, virulence to the widely used Sr31 resistance gene has been reported from Kenya, Ethiopia, Sudan, and Iran (2,3). In November 2009, a wheat genotype suspected to carry Sr31 showed a susceptible response to stem rust in a disease nursery (29°08'05.02''S, 30°38'29.18''E), inoculated with race TTKSP, near Greytown in KwaZulu-Natal, South Africa. Inoculation of urediniospores of the field collection (isolate UVPgt60) onto seedlings of line Federation4*/Kavkaz confirmed virulence for Sr31. In three independent, replicated, and comparative seedling tests, eight single-pustule isolates of UVPgt60 all typed to race PTKST following the NA race nomenclature. These isolates produced compatible infection types (ITs) (3+ to 4) on the Sr31 testers Gamtoos, Sr31/6*LMPG, Federation4*/Kavkaz, Kavkaz, and Clement, whereas isolate UVPgt59 (TTKSP) was avirulent (ITs ;1 to 1) on these genotypes. In addition to Sr31 virulence, the new race differed from TTKSP by producing a lower IT (2 to 2++) on Cns_T.mono_ deriv., the accepted entry for Sr21 in the NA differential set. The UVPgt60 isolates were clearly avirulent on Einkorn (Sr21) (IT ;1=), a response that also differed from those produced by BPGSC, TTKSF, and TTKSP (IT 2). With the exception of Sr21, UVPgt60 isolates had a virulence pattern similar to race TTKST (1), notably the virulence combination for Sr24 and Sr31. Isolate UVPgt60.6 was randomly selected for testing on additional Sr genes and South African wheat cultivars and breeding lines. Similar to the race identification experiments seedling tests were duplicated and compared with reactions produced by TTKSP and other races. Greenhouse temperatures for all seedling tests ranged between 18 and 25°C. On the basis of primary leaf responses, PTKST is avirulent (ITs 0; to 2++) for Sr13, 14, 21, 22, 25, 26, 27, 29, 32, 33, 35, 36, 37, 39, 42, 43, 44, Em, Tmp, and Satu and virulent (ITs 3 to 4) for Sr5, 6, 7b, 8a, 8b, 9a, 9b, 9d, 9e, 9g, 10, 11, 16, 17, 24, 30, 31, 34, 38, 41, and McN. From 103 South African wheat cultivars and lines tested as seedlings, 59 and 47 were susceptible (IT ≥ 3) to races PTKST and TTKSP, respectively. Simple-sequence repeat analysis (4) with selected primer pairs showed that PTKST clusters with isolates belonging to the Ug99 lineage. Subsequent to the collection made at Greytown, stem rust sampled in December 2009 from naturally infected breeders' lines at Cedara (29°32'19.59''S, 30°16'03.50''E), KwaZulu-Natal, revealed five isolates with a virulence profile similar to PTKST. On the basis of current evidence it appears that PTKST may be an introduction to South Africa rather than a single-step mutation from local stem rust races.

Grain yield, nitrogen uptake and use efficiency components of South African irrigation wheat cultivars under different nitrogen management strategies

The effect of different N management strategies on the grain yield, N uptake and use efficiency components of five commercial wheat cultivars were investigated for two consecutive years at Riet River and Loskop irrigation schemes. The cultivars ranged ingrowth period to initial flowering, from 95, 102, 106, 108 and 109 days for SST 822, Steenbras, SST 876, Olifants and Baviaans. Management strategies consisted of zero (NO) and recommended Napplication split-applied at different growth stages (N1 = 100% at planting; N2 = 54% at planting, 23% at stem elongation and 23% at flag leaf; N3 = 38% at planting, 44% at stem elongation and 18% at flag leaf; N4 = 100% at stem elongation in the first year, and 37% at planting and 63% at stem elongation in the second year). The lowest grain yield and N uptake resulted for N0, followed by N4 and then either N1, N2 and N3. The longer-growing Baviaans, Olifants and SST 876 (more than 106 days to flowering) responded more to N fertilization than the shorter growing Steenbras and SST 822 (less than 102 days to flowering). This also applied to grain yield, N uptake and N harvest index. The cultivars SST 822 and Steenbras had the lowest and SST 876 the highest N physiological efficiency (NPE). Application of N had limited effect on the agronomic (NAE) and recoveryefficiency (NRE) of the element. The results of this study showed that several factors must be considered in the selection of N efficient wheat cultivars.

Significance of kernel moisture content in determination of Hagberg Falling Number in wheat

The effect of early termination of kernel filling (early harvest) on the Hagberg Falling Number (HFN) was investigated over a four-year period. Selected South African wheat cultivars were harvested at different stages of kernel development, determined by kernel moisture content (KMC). HFN was determined at each stage of development. Difficulty in obtaining sufficient data points at each KMC necessitated the creation of two KMC ranges: 10–13.1% and 13.2–16.9%. Alpha-amylase activity was determined for each of the cultivars at the various KMCs during the 2003/04 and 2004/05 seasons. Data generated with three wheat cultivars (Elands, Gariep and Tugela-DN) over a four-year period indicated that the effect of KMC with harvest on the HFN of wheat is season dependant. Tugela-DN produced significantly (P≤0.05) higher HFN at the lower KMC range (10–13.1%) for two (2001/02 and 2004/05) of the four seasons during this study. Gariep showed similar results to Tugela-DN for the 2001/02 season. For Elands, the HFN remained constant over the four seasons at the various KMCs. Although there were no statistically significant differences between cultivars, it was observed that higher HFNs occurred at the lower KMC range. The effect of alpha-amylase activity at the KMC investigated in the study could not be successfully linked to reduced HFN measured at the higher KMC range. Late maturity alpha-amy-lase (LMA) was also excluded as a possible reason for reduced HFN. The current study indicated that some cultivars are prone to produce higher HFNs at lower KMCs but that the effect is limited to specific seasons.

Use of Size‐Exclusion High‐Performance Liquid Chromatography for Wheat Quality Prediction in Ethiopia

ABSTRACTWheat quality testing facilities in Ethiopia are limited. The aim of this study was to determine whether size‐exclusion high‐performance liquid chromatography (SE‐HPLC) could be used in breeding programs for quality testing. Thirteen Ethiopian and two South African wheat cultivars were evaluated in two diverse environments for milling and dough characteristics. SE‐HPLC was done on the same samples. Across environments, both SDS‐soluble and SDS‐insoluble polymeric proteins significantly influenced important quality characteristics such as SDS‐sedimentation and mixograph development time. The large monomeric proteins, which are mainly gliadins, had a consistently significantly negative effect on quality. The increase of polymeric protein as opposed to monomeric protein led to improvement of quality characteristics. The SDS‐soluble and SDS‐insoluble polymeric proteins were equally important in quality prediction. The amount of polymeric proteins was significantly higher in the high‐protein environment. Despite a large environmental effect on most fractions, a large ratio of polymeric proteins to monomeric proteins (both SDS‐soluble and SDS‐insoluble) can be a good indicator of baking quality. SE‐HPLC is therefore an option to use in breeding programs in Ethiopia for quality evaluation.

The influence of eyespot resistance genes on baking quality and yield in wheat

AbstractIn a backcross programme to introduce resistance genes, the retention of genes other than the resistance gene from the donor parent is possible owing to either chance, the simultaneous transfer of linked genes, incomplete compensation of replaced wheat chromatin, or other crossover segments being incorporated into the wheat genotype. This may cause unwanted characteristics in resistant cultivars. Eyespot in wheat is caused by Pseudocercosporella herpotrichoides (Fron) Deighton. This disease is widely spread throughout the world and can result in severe damage to wheat crops. Genetic control of the disease has been found to be very effective. The aim of this study was to determine the effect of the Pch1 eyespot resistance gene, backcrossed 8–10 times into South African wheat cultivars SST66 and Palmiet, on baking quality and yield in the absence of the disease. The presence of the gene had a detrimental effect on thousand‐kernel mass in two SST66 lines and on yield in one Palmiet line, but there were no detrimental effects on any measured quality characteristics. The presence of the gene will thus protect the plant from the disease without having a negative effect on baking quality.© 2002 Society of Chemical Industry

Reaction of South African spring wheat cultivars to head blight caused by Fusarium graminearum

Head blight caused by Fusarium graminearum (Schwabe) is an important wheat (Triticum aestivum L.) disease in the centrepivot irrigation areas of South Africa. Fifteen cultivars, Gamtoos, Inia, Kariega, Marico, Nantes, Palmiet, SST 38, SST 55, SST 57, SST 65, SST 66, SST 822, SST 825, SST 876, T4 and two breeding lines, Potch 92 and Potch 93 were evaluated in the greenhouse for their ability to resist the development of head blight (Type II resistance). Following inoculation of a single spikelet (growth stage 61) with a mixture of two F. graminearum isolates, disease progress in each cultivar was assessed over a 20 day period. Fourteen days after inoculation less than 29% of the spikelets of Gamtoos, T4 and Potch 93 were infected whilst Inia, Palmiet, SST 65, SST 825 and SST 876 had infection levels equal or above 58%. Kariega, Marico, Nantes, SST 38, SST 55, SST 57, SST 66, SST 822 and Potch 92 indicated an intermediate head blight response with disease severity differing between 36 and 48%, 14 days after inoculation. These results will be followed by evaluations for resistance to penetration (Type I) and ability to suppress toxin production (Type III).

Resistance in South African and foreign wheat cultivars to pathotypes 6E16A- and 6E22A- of Puccinia striiformis f. sp. tritici

Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks., has become an endemic disease of wheat (Triticum aestivum L.) in South Africa after being observed for the first time near Moorreesburg, Western Cape, during August 1996. The reaction of 55 South African and 18 foreign Triticum aestivum L. cultivars was determined to pathotypes 6E16A- and 6E22A- in the seedling and adult plant stage. The occurrence of stripe rust head infections was studied in 16 spring wheat cultivars and 17 supplemental lines. Six of the 55 local wheat cultivars expressed seedling resistance (infection type < 2+), 18 appeared heterogeneous and 31 were susceptible (infection type ≥ 2+). The mean area under the disease progress curve (AUDPC) determined in the field for 42 cultivars over a three year period showed that 11 cultivars expressed high levels of complete or adult plant resistance (AUDPC < 200). Twelve cultivars displayed intermediate levels of resistance (AUDPC 200 to 500) and 19 displayed AUDPC values of 500 to 1598. Terminal severity ratings were highly correlated with AUDPC for both winter (R2 = 0.91, P > 0.001) and spring (R2 = 0.82, P < 0.001) wheat cultivars. Stripe rust resistance expressed by local wheat cultivars appeared stable over five different environments. The percentage head infection was positively correlated (R2= 0.78, P < 0.001 during 1997 and R2= 0.84, P < 0.001 during 1999) to stripe rust severity on flag leaves. Cultivars and lines with seedling resistance showed no or a very low percentage (0 to 2%) head infection, whereas cultivars susceptible in both seedling and adult plant stages were severely infected in the heads. Cultivars and lines expressing adult plant resistance showed intermediate to low percentages of head infection. Of the 18 foreign cultivars evaluated 10 were resistant in both seedling and adult plant stages. The remaining eight cultivars were susceptible as seedlings but showed high levels of adult plant resistance in the field.

Biotypic differences in Russian wheat aphid ( Diuraphis noxia) between South African and Hungarian agro-ecosystems

The effect of Russian wheat aphid Diuraphis noxia (Mordvilko) from South Africa and Hungary was measured on susceptible and resistant South African wheat cultivars and a susceptible Hungarian barley cultivar. For the three cultivars (‘SST 333’, ‘Betta’, and ‘Isis’) tested in both countries, Hungarian D. noxia reduced plant weight and leaf area more than South African D. noxia and this difference increased over time. Hungarian D. noxia reduced plant weight and leaf area of the resistant wheat SST 333 more than the susceptible wheat Betta. Hungarian D. noxia also reduced plant weight of the resistant wheat ‘PI 262660’ more than the susceptible wheat Betta (although the opposite was true for leaf area). In Hungary the resistant SST 333 and PI 262660 showed similar severe symptoms of yellowing and leaf rolling as susceptible Betta. In addition, Hungarian D. noxia caused visible water imbalance in resistant wheats SST 333 and PI 262660. The differences in damage did not result from higher growth rate of Hungarian D. noxia colonies because aphid numbers did not differ consistently between countries or match the differences in damage. Differences between Hungarian and South African D. noxia suggest genetic differences between these populations. These results support the idea that resistant plant germplasm has geographical limits because of variation in agro-ecosystems.

Genetic relationships between South African wheat cultivars as measured by gliadin banding patterns

The use of gliadins in cultivar identification is a well-known practice that is used in many countries. The aim of this study was to determine the gliadin banding patterns of 35 commercial South African wheat cultivars and to use these data to determine genetic relationships between the cultivars using sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The index of genetic similarity was used to calculate pairwise distance matrices, which were converted to a dendogram. Most of the gliadin bands fell within the nomenclature used. Fourteen cultivars had one novel band and six had two novel bands. All the cultivars could be distinguished from one another. Genetic distances between clusters were small. This suggested that there was not enough unique genetic variability to set any cluster apart from the others.