ITEMS FROM SOUTH AFRICA

SMALL GRAIN INSTITUTE

Private Bag X29, Bethlehem, 9700, South Africa.

Because of low wheat price, high input costs, unfavorable weather conditions, and standards set by the "new free market environment" that has ruled South Africa since the end of 1997, wheat production has decreased drastically. Thus, wheat research is becoming increasingly important to aid the farmers in producing a cost-effective crop.

Winter and intermediate wheat breeding.

H.A. van Niekerk, J.C. Aucamp, O. Müller, and D.J. Exley.

Traditionally, between 50 % and 60 % of the total wheat production in South Africa can be accounted for by dryland wheat production in the summer rainfall region and results from the planting of mainly winter and intermediate bread wheat types in the Eastern, Central, and Western Free State. However, we are concerned that farmers planted 56 % less wheat (during 1998) than the 790,000 ha that was planted in the previous year.

The goal of research is to develop improved, high-yielding, well-adapted and stable cultivars of winter and intermediate wheat for dryland conditions in the Free State. Furthermore, these cultivars have to completely meet all the quality requirements set by the processing industry. To help reduce the farmer's risk, cultivars must have a high falling number; very good preharvest sprouting resistance; and resistance to disease (especially yellow, stem, and leaf rusts) and RWA to help the farmer reach maximum yield and keep input costs as low as possible.

The highlight of this past season was the release of Elands, an intermediate-type wheat cultivar, which almost complies with the above-mentioned idiotype. Elands is a high-yielding, well-balanced, bread wheat with high flour extraction, high water absorption, good mixing characteristics, and excellent protein quality. The cultivar completely meets with all the quality requirements of the new market environment in South Africa. Elands is resistant to stem rust, but unfortunately is susceptible to leaf and yellow rusts. Elands has very good RWA resistance, excellent preharvest-sprouting resistance, and exceptional hectoliter mass. This cultivar will be planted commercially for the first time during the 2000 wheat season.

Spring wheat breeding.

H.A. van Niekerk, A.D. Barnard, M.S.S. Jordaan, and T.G. Paxton.

Dryland conditions. The objective of spring wheat breeding is to develop and release improved high-yielding, well-adapted, stable cultivars superior for one or more important characteristics. The Western Cape is traditionally a low protein environment. Grain quality consists of a number of characteristics that are influenced by different factors, some genetic, some environmental, and some both. To successfully increase the most important quality characteristics and yield simultaneously, the choice of breeding parents is extremely important. Therefore, a study was undertaken to identify suitable parental lines that are stable over environments, which can be used to produce superior progeny for yield and quality characteristics in the Western Cape.

Six parental lines were planted at the Langgewens (Swartland) and Tygerhoek (Rûens) experimental farms. The climatic conditions and soil types of these two localities differ completely. A randomized complete block design with four replications was used. An ANOVA was performed, and showed locality, cultivar, and the 'locality x cultivar' interaction.

Some cultivars were more stable over environments; therefore, parents should be selected on good average performance across localities. From this study, three stable cultivars (Kariega, SST 57, and Palmiet) were identified as useful for the improvement of quality characteristics. Because of their stability across environments, the genotype plays a more important role in the expression of these traits. No stable-yielding cultivar was identified. Gamtoos proved to be the best parental line to improve both farinograph absorption and stability, but because of the negative association of the T1B·1R translocation with quality, this cultivar should be used to a limited extent.

Irrigation conditions. This breeding program is responsible for developing short-stature, spring wheat cultivars for the warmer and cooler irrigation areas.

The requirements for a new cultivar evidently intended for irrigation include the following:

• good and stable yield across environments;
• outstanding bread-baking quality characteristics (including hectoliter mass, protein content, extraction, mixograph mixing time, farinograph water absorption, alveograph strength, extensibility and P/L value, and bread volume);
• outstanding agronomic characteristics (lodging, growth period, vernalization requirements, and day length sensitivity); and
• disease resistance (leaf rust, stem rust, yellow rust, maize stripe virus, bacterial blight, take-all, mildew) and aluminium and salt tolerance.

Since 1990, the cultivars Marico (1992) and Kariega (1993) were released from this program. Currently, breeding varieties able to hold up to the outstanding bread-making quality characteristics of Kariega is extremely difficult.

New and future releases from the breeding program. The Wheat Technical Committee accepted KBSP95/26 for final classification, and this line will be marketed as Steenbras. BSP 97/1 was classified provisionally and will be sent for final classification at the end of this season. The average yield data for Steenbras (Fig. 1) show that the yield averages for later planting dates in the irrigation areas compare well to that of Palmiet. This cultivar also is a higher-yielding double dwarf than SST 822.

The yield performance of BSP 97/1 compares well to that of Kariega, whereas its hectoliter mass is higher and more stable over environments. The agronomic data for Steenbras and BSP97/1 are shown in Table 2.

New and interesting germ plasm developments. Thirteen lines selected from the drought-tolerance trial during 1997, together with five local standards, were evaluated in two trials at the Upington research station. The control trial received optimal irrigation, whereas the other trial was evaluated under water-deficient conditions. Both these trials were screened for heat tolerance with an infrared gun. CIMMYT researchers use canopy temperature depression (CTD) as a rapid, early generation screening tool for heat tolerance in wheat. The data still need to be analyzed statistically. If this technique can be implemented successfully at SGI, it would be possible to develop lines capable of keeping up their performance under water-deficient conditions. These lines can further reduce the risk and input costs for the irrigation farmer in a country with poor water resources.

A take-all trial at Potchefstroom was conducted for the second time to determine the resistance levels of all the most popular spring wheat cultivars currently in production in the summer and winter rainfall areas. A total of 13 cultivars, including Potch 92 and Potch 93, which showed high levels of resistance during the previous season, were evaluated. The aboveground infection was expressed as a percentage of the infected plants in each row compared to the total amount of plants in each row. Potch 92 and 93 again showed lower susceptible percentages than all the commercial cultivars, except SST 57. Potch 92 showed the best resistance, and T4 showed acceptable resistance levels. The F2 population, from crosses between Potch 92 and 93 with Kariega and other parents, was planted at the same locality. Five spikes were selected from rows that showed less than 15 % white spikes. These spikes were bulked and will be evaluated in the F3 generation at the same locality this season.

Nitroweat is a bacterial inoculant used on small grain crops like wheat in order to enhance root growth and nutrient uptake. Six trials were planted in the irrigation areas. Each trial consisted of large strips split into a control and a Nitroweat treatment. Small plots, each 1 m2, were cut from each trial. Hectoliter mass, yield, and protein content were determined for these samples. A minimum of 12 samples/treatment was taken at each locality. This data show significant positive increases in profits except for Delmas, where the trial was harvested too early, which negatively influenced hectoliter mass. The differences between the control and treatment for each locality are in Table 3.

New genetic diversity.

A.D. Barnard and A. Otto.

To prevent genetic narrowing, new germ plasm is evaluated annually for agronomic traits, disease resistance, and quality in the International Nurseries project. This evaluation is very critical and includes a wide array of germ plasm, which is collected on a worldwide scale. Most of these genotypes are recently developed and unique, representing the cream-of-the-crop from the previous year. During the past 3 years, these lines were especially useful for selecting sources of stripe rust resistance to a disease that currently occurs widely in South Africa. Various numbers of new sources of genetic diversity are obtained on a regular basis from CIMMYT (Mexico), the U.S.A., Turkey, Germany, Spain, and Romania. During the past season, wheat and barley lines from the ICARDA program in Syria also were added. Selections of lines from these nurseries and programs are included in the various breeding programs at the Small Grain Institute to further the development of suitably adapted cultivars for the wheat industry in South Africa. Purposeful crosses also are performed on outstanding germ plasm.

Quality laboratory.

H.A. van Niekerk, F.P. Koekemoer, C.W. Miles, K.B. Majola, and M.L.T. Moloi.

The wheat quality laboratory has completed the analyses of the South African wheat cultivars to determine the relative milling and baking worth, including bran carrying capacity, on a scientific and selection-index basis. The information obtained from these analyses will create clear market signals as to what the market requires and lead to concomitant higher prices for improved quality. Therefore, this laboratory has become an integral part of the breeding programs at the Small Grain Institute. Other departments at the Small Grain Institute, wheat producers in the area, small millers, and universities make use of this laboratory and contribute to the more than 50,000 analyses performed by this laboratory each year.

Biotechnology-double-haploid technique.

A.F. Malan and M. Ncala.

During the past 5 years, a protocol was developed to suit the needs of the Small Grain Institute for doubled haploids of wheat. Maize-wheat crossings were used to achieve the goal. Several maize pollinators and hormone treatments were tested, but the best results were achieved with the U.S. cultivar Miricle, followed by two consecutive treatments with the hormones 2,4-D and gibberellic acid.

This technique was standardized and currently is applied as a routine protocol in the tissue culture laboratory at the Small Grain Institute. The technique is used extensively on the early generation, segregating material to produce large amounts of pure breeding lines for selection purposes.

Furthermore, this laboratory is responsible for generating double-haploid material for the SGI barley breeding program. Between 15,000 and 20,000 anthers are placed on medium per year.

Biotechnology-molecular and tissue culture techniques.

R. Prins, V. Ramburan, and W.H.P. Boshoff; L.A. Boyd and T. Worland (Cereals Research department John Innes Centre, UK); Z.A. Pretorius (Plant Pathology Department, University of Free State, RSA); and J.H. Louw (University of Stellenbosch, RSA).

Results from a 'Kariega/Avocet 'S'' F2 population suggested that unidentified adult plant resistance to yellow rust in the South African wheat cultivar Kariega is not monogenic and that a quantitative genetics approach, employing QTL mapping procedures, should be followed. A DH-mapping population consisting of 150 lines has been developed by the wheat-maize technique from a 'Kariega/Avocet 'S'' cross, and AFLP and SSR markers were identified in the two parents. The primary aims are to increase the number of markers in order to cover the entire genome as far as possible and also to search for RFLP markers in regions where useful SSR markers cannot be identified. Initial greenhouse tests for adult plant resistance in genetic material derived from Cappelle Desprez shows that Yr16 (APR) is effective against the South African pathotypes (6E16 and 6E22). This material will undergo further testing in field trials this year. Should the result be confirmed, the Yr16 (APR) gene will be used in the breeding programs.

Soil management-soil acidity.

HJJ van Zyl.

Soil acidity is the most severe chemical limitation of crop production in the Eastern Free State. Continuous soil cultivation accelerated the natural process of acidification to such an extent that 75 % of the regions soils have pH-values of 4.5 (KCl) and lower. The stressful environment in which the plant is grown and an excess of aluminium in the soil can cause severe damage to the roots, resulting in significant yield losses.

The response of three wheat cultivars differing in aluminium tolerance was measured at different lime levels. Biomass and yield indicated that Tugela-DN (good tolerance) could produce economical yields on acid soils. The yield of Tugela-DN increased significantly when lime was applied. Gariep (medium tolerance) and Limpopo (susceptible) were not able to produce economical yields on acid soils. Liming increased the yield of both these cultivars to economic levels.

Soil management-micronutrients.

H.J.J. van Zyl.

Various soil factors influence the availability of micronutrients for plant uptake. Even though micronutrients are utilized in small amounts by the plant, they play an important roll in the physiology of the plant. When deficiencies of one or more of these elements occur, normal growth and production are not possible.

The influence of micronutrient foliar applications on wheat yield and quality were investigated. Different micronutrient products were applied at different growth stages. No significant differences were found between the different products. An early application ± 40 days after planting produced higher yields than applications at flag-leaf stage (± 90-100 days after planting). The protein content and hectoliter mass were not significantly different between the treatments.

Soil management-nitrogen applications under irrigation.

W. Otto, W. Kilian, H.C.S.A. van der Merwe, E. van der Merwe, B. van Rensburg, and C. Fourie.

Trials were planted in the Vaalharts-, Riet River-, and Loskop-irrigation schemes to evaluate the influence of split applications of nitrogen on the growth, yield, and grain quality of wheat cultivars. Kariega and SST 825 were planted at Vaalharts and Riet River, whereas Kariega and SST 822 were planted at Loskop. Nitrogen was applied at planting, at early and late tillering, and at the flag leaf/ear emergence growth stages. A total of 200 kg N/ha was applied at Vaalharts and Riet River and 175 kg N/ha at Loskop.

Yield levels in the trials in 1998 were on average 4 t/ha at Loskop and up to 8 t/ha at Vaalharts and Riet River. The split application of N resulted in significant yield responses. The split applications of 100-125 kg N/ha at Loskop and 125-150 kg/N ha at Vaalharts and Riet River applied at planting, followed by 25 kg N/ha applied at late tillering, and 25-50 kg N/ha at flag leaf stage produced yields of 8.2 to 8.4 t/ha (Riet River), 5.9 to 6.3 t/ha (Loskop), and 9.3 to 9.9 t/ha (Vaalharts). This treatment also produced the highest hectoliter mass of the grain, which indicates the positive effect of N applications on kernel size and weight during the later growth stages. Protein content of the grain was increased by application of N at the flag-leaf stage, with average increases of 0.51 % (Riet River), 0.29 % (Loskop), and 0.32 % (Vaalharts). These results indicate that the management of N up to the late-tillering stages is aimed at optimizing yield potential, and N applications during the later growth stages will benefit grain protein content. The results from this project are of great importance to the wheat producer in the current marketing system. They allow recommendations to producers regarding the amount of N and split applications of N to reach yield potential levels and produce acceptable levels of grain quality. The future aim of this project is to calculate and predict the contribution of N by the soil, determine N uptake curves of cultivars, and to use the resulting values to further adapt the N recommendations.

Soil management-long-term phosphorus in combination with nitrogen applications.

W. Otto and W. Kilian.

This project consists of a long-term trial site. In one trial, the long-term effect of phosphorus applications (0-45 kg P/ha, applied since 1983) on yield and soil analyses was determined. On an adjacent site (NXP), the effect of phosphorus applications (0-32 kg/ha) in combination with nitrogen applications (0-60 kg N/ha) on yield and soil analyses data were evaluated.

The soil analyses showed that the soil P values changed relatively slowly in response to P applications. The initial value of 12.5 mg/kg (Bray 1) changed to 11 mg/kg on the plots receiving no P application and increased to 38 mg/kg at the 45 kg P/ha level of application. Yields increased significantly in the long-term P trial (1983-97) (average yields were 1.8 ton/ha) with application of P up to 10 kg P/ha, but no differences occurred in measured yields between the 10-45 kg P/ha levels.

A similar response pattern was found in the NXP trial, with increases in yields up to the 8 kg P/ha level, but with no further significant yield responses up to the 32 kg P/ha level. Yields were increased with N applications up to the 30 kg N/ha level, but no differences occurred between the 30 to 60 kg N/ha levels. Protein levels of the grain were increased with nitrogen applications, and the largest response occurred at the 45-60 kg N/ha levels.

These results confirm the current recommendations for nitrogen and phosphorus applications under rain-fed conditions, at the yield levels measured in these trials. Furthermore, these results indicate the importance of balanced fertilizer application for the production of high-quality grain.

Soil management-soil nitrogen and nitrogen applications.

W. Otto, W. Kilian, and T. Steyn.

The aim of this project is to determine the influence of soil nitrogen applications on growth and yield of wheat. The project is conducted on trial sites representing three of the major wheat production areas in the summer rainfall region of the Free State Province. These trial sites are at Petrusburg (Western Free State), Kroonstad (Central Free State), and Bethlehem (Eastern Free State). Wheat was cultivated in a fallow-wheat/wheat-fallow rotation system, with nitrogen levels of 0 up to 60 kg N/ha applied. Aboveground biomass development and the N-uptake pattern in combination with soil N analyses were measured on selected treatments.

Initial soil mineral N content at planting (1997) indicated relatively high values of residual N in the profile (0-1,200 cm) following the fallow period (Petrusburg: 185, Kroonstad: 260, and Bethlehem: 299 kg N/ha). Biomass development was increased by N applications, but heat and moisture stress during the later growth stages depressed the response and yield levels. Average yields of 2.2 t/ha at Kroonstad, 0.9 t/ha at Petrusburg, and 2.4 t/ha at Bethlehem, were produced. Yields were increased significantly with N applications, with responses up to the 10-20 kg N/ha levels at Petrusburg, the 20-30 kg N/ha levels at Kroonstad, and the 30-45 kg N/ha levels at Bethlehem. Grain-protein content increased in response to increased N application: from 13.4 to 11.5 % (0 to 60 kg N/ha) at Kroonstad, from 11.8 to 12.2 % (0 to 30 kg N/ha) at Petrusburg, and from 10.1 to 12.3 % (0 to 60 kg N/ha) at Bethlehem.

Compared to 1997, the 1998 data showed lower yields and grain-protein contents at Bethlehem and Kroonstad and a similar response at Petrusburg. Lower soil mineral N values at the start of the growing season (Petrusburg: 45-50, Kroonstad: 116-150, and Bethlehem: 147-199 kg N/ha) and lower rainfall during the 1998 growing season partly of the explain the decrease. At Kroonstad, average yield levels were 0.9 t/ha, with no response to N applications, but grain-protein content increased from 10.9 to 11.5 % as N applications increased to 60 kg N/ha. Average yields of 1.88 t/ha were recorded at Bethlehem; positive responses occurred in yield to increased N applications (45-60 kg N/ha) and in protein content (9.1 to 10.0 %) with applications up to 60 kg N/ha. At Petrusburg, yields were increased at applications of 30-40 kg N/ha, which resulted in lowered protein values (13.6 to 10.5 %) for these treatments.

These response patterns indicate that in a wheat-wheat rotation system, N can become deficient, resulting in lowered yields and reduced grain-protein content, although lower yields also can occur as a result of moisture availability and rainfall distribution. Nitrogen response is in accordance with the current N recommendations for wheat production under rain-fed conditions at the yield levels produced. The possible effect of soil mineral N values, in combination with N applications on growth and yield, is influenced to a large extent by climatic conditions (rainfall and temperature) during the growing season. The interaction between these parameters must be investigated to integrate soil N analyses values into fertilizer recommendations.

Soil management-conservation tillage.

J.T. Steyn.

No-till. No-till has not been kind to maize farmers who tried the practice during the 1980s, because of the Diplodia crop-rot epidemic. However, deregulation of the crop industry and the high input cost/producer price squeeze have forced crop producers to consider alternative farming practices. Conservation tillage, including no-till, is once again considered a respectable crop-production technique. Two reasons are the availability of no-till planters today, which was not available a few years ago, and the increase information about no-till farming system.

No-till requires the highest level of management skills of all the forms of cultivation, conventional tillage included. One reason is that a very high degree of understanding of the requirements of the technique is necessary. A very definite change in mindset from that for conventional tillage is required, and once the mindset has been acquired, one really has arrived.

Minimum tillage. Tillage costs have risen drastically in the last few years, especially during 1996 and 1997. The weakening of the Rand against overseas currencies and elimination of the diesel subsidy to farmers are the most important reasons. Trial results indicated that input costs could be reduced when chemical weed control is used together with mechanical weed control practices. Furthermore, the results indicated that nitrogen levels should be increased during wet seasons to compensate for nitrogen loss through leaching and negative periods. Not burning stubble resulted in higher yields during 1997.

Entomology-Russian wheat aphid.

V.L. Tolmay, G.J. Prinsloo, J.H. Hatting, and R. Maré.

The Small Grain Institute is implementing an integrated program for control of the RWA. The basis of this program is the use of RWA-resistant cultivars; natural enemies of the aphid and cultural practices support these cultivars. Chemical control is intended to be used only when extremely high infestation levels occur. Six wheat cultivars with RWA resistance have been released by the SGI for commercial production in South Africa to date. They are Tugela-DN, Betta-DN, Gariep, Limpopo, Caledon, and Elands. A backcross program will transfer RWA resistance to agronomically acceptable lines for use in the winter and intermediate wheat breeding programs. Resistant cultivars released for commercial use are tested under field conditions, with and without chemical control methods, to determine the value of these cultivars. All resistant cultivars tested so far give yield and hectoliter advantages. The parasitoid Aphelinus hordei is being released in the field for the fourth year. More than 1.5 million individuals were released on six farms in the Eastern Free State. Second-year field trials with A. hordei show3e that this parasitoid is able to reduce RWA populations significantly on both susceptible and resistant wheat cultivars early in the season. Entomopathogenic fungi are being investigated simultaneously for development as mycoinsecticides against the cereal-aphid complex. Two hyphomycetous species, Beauveria bassiana and Paecilomyces farinosus, are being screened for their virulence against the RWA and other important cereal aphid species. Techniques for mass production of suitable indigenous isolates by both solid substrate fermentation and liquid fermentation are being investigated currently. Field trials with an exotic strain of B. bassiana (Mycotrol®) indicates that a commercial preparation of this pathogen is capable of significantly reducing RWA numbers on resistant wheat.

Plant pathology-leaf rust.

B.D. van Niekerk and O. Meintjes.

Leaf rust epidemics occurred in the Western and South Western Cape during the 1999 season and possibly can be attributed to the warmer weather early in the season and the susceptibility of cultivars planted in these regions. Only two pathotypes were identified, 3SA133, which dominated 95 % of the isolates, and 2SA140, comrising the other 5 %. Pathotype 3SA133 has virulence to resistance genes Lr1, Lr2c, Lr3a, Lr3ka, Lr10, Lr11, Lr14a, Lr20, and Lr24, and pathotype 3SA140 has virulence to resistance genes Lr1, Lr2a, Lr2b, Lr2c, Lr10, Lr14a, Lr15, Lr17, Lr24, and Lr26.

Notwithstanding the dry conditions earlier in the season, severe leaf rust epidemics occurred on barley along with the breakdown in the resistance of the cultivar SSG 532, which has the resistance gene Rph12. All South African barley cultivars are now susceptible to leaf rust.

Preharvest sprouting.

A. Barnard.

The major objective in preharvest-sprouting research is to solve the problems experienced by the cereal producers and the cereal industry. The major aims of this study are to characterize newly released cultivars, determine their sensitivity to the environment (G X E), and evaluate advanced breeding lines for their preharvest-sprouting tolerance.

The eastern parts of the Free State especially were subjected to heavy rainfall, and a considerable amount of wheat was lost from preharvest sprouting coupled with low falling numbers. More emphasis will be placed on falling number and a-amylase activity in future.

Seed-testing laboratory.

F. van Niekerk.

Seed plays a vital role in the potential crop yield of each small grain producer. Small grains must comply with the legal requirements for purity and germination percentage before they can be marketed. The Small Grain Institute now has an accredited Seed Testing Laboratory where international methodology of the International Seed Testing Association is used to determine the quality characteristics of seed.

The demand for genetic-purity testing, determined visually, has increased tremendously among seed companies and has accounted for 662 tests in the past year. For cultivar identification, 27 samples, analyzed during the grading of small-grained seed in accordance with the Southern African Grain Laboratory, resulted in 472 tests by the laboratory. The germination and purity testing over the past year resulted in 498 analyses, several of which identified seed lots not complying with the South African Plant Improvement Act. The laboratory provides a unique service and has the infrastructure and experience to conduct seed analyses objectively on a commercial and need-driven basis for the seed industry.

A number of contracts were finalized with chemical companies concerning the evaluation of seed treatments on wheat and maize. This work contributed favorably to the income of the Seed Testing Laboratory. The services were client-specific and extended the commercial services of the laboratory.

Personnel.

Suzette Jordaan resigned from the spring wheat breeding program at the end of March 2000. Felix Middleton was appointed as the plant breeder in this program during January 2000. Robbie Lindeque and Johan Smith resigned from the plant protection division. Kobus van Zyl was married during December 1999.

Publications.

• Barnard A and Purchase JL. 1999. The relationship of preharvest sprouted seed and seed treatment to emergence and yield of winter wheat (Triticum aestivum L.) in the Eastern Free State. Seed Sci Technol 26:711-718.
• Barnard A and Pretorius JC. 1999. The possible role of the oxidative pentose phosphate pathway in seed dormancy in winter wheat cultivars. Seed Sci Res (submitted).
• Boshoff WHP, Pretorius ZA, and Swart WJ. 1999. A comparison of head infection and blight development caused by Fusarium graminearum and Fusarium crookwellense in wheat. South Afr J Plant Soil 16(2):79-84.
• Boshoff WHP, Pretorius ZA, and Swart WJ. 1999. In Vitro differences in fungicide sensitivity between Fusarium graminearum and Fusarium crookwellense. Afr Plant Protect 5(1):65-71.
• Boshoff WHP and Pretorius ZA. 1999. A new pathotype of Puccinia striiformis f sp. tritici on wheat in South Africa. Plant Dis 83(6):591.
• Boshoff WHP, Swart WJ, and Pretorius ZA. 1999. Isozyme characterization of Fusarium graminearum isolates associated with head blight of irrigated wheat in South Africa. South Afr J Bot 65(4):281-286.
• Boshoff WHP, Van Niekerk BD, and Pretorius ZA. 1999. Pathotypes of Puccinia graminis f.sp. tritici detected in South Africa during 1991-1997. South Afr J Plant Soil 16(2):79-84.
• De Villiers BL, Smit HA, Lindeque RC, and Smit JJ. 1999. Optimizing MCPA (K-salt) activity with salt adjuvants. South Afr J Plant Soil (accepted).
• Hatting JL, Poprawski TJ, and Miller RM. 1999. Managing the entomopathogenic fungus Conidiobolus thromboides in Russian wheat aphid Cultures. Southwestern Ent 24:99-106.
• Hatting JL, Humber RA, Poprawski TJ, and Miller RM. 1999. A survey of fungal pathogens of aphids from South Africa, with special reference to cereal aphids. Biological Control 16(1):1-12.
• Koekemoer FP, Labuschagne MT, and Van Deventer CS. 1999. Selection strategy for combining high yield and high protein content in South African wheat cultivars. Cer Res Commun 27(1-2):107-114.
• Prins R and Marais GF. 1999. An extended deletion map of the Lr19 translocation and modified forms. Euphytica 103:95-102.
• Prins R and Marais GF. 1999. A genetic study of the gametocidal effect of the Lr19 translocation of common wheat. South Afr J Plant and Soil 16(1):10-14.
• Prinsloo GJ and Du Plessis U. 1999. Temperature requirements of Aphelinus sp. (Hymenoptera: Aphelinidae) a parasitoid of the Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae). Afr Ent (accepted).
• Robbertse B, Lennox CL, Van Jaarsveld AB, Crous PW, and Van Der Rijst M. 2000. Pathogenicity of the Rhyncosporium secalis population in the Western Cape province of South Africa. Euphytica (accepted).
• Smit JJ, Smit HA, and De Villiers BL. 1999. Differential efficacy of Tralkoxydim and Diclofop-Methyl on a suspected resistant ryegrass (Lolium multiflorum L.) biotype. South Afr J Plant and Soil 16(4):69-172.
• Smit JJ, De Villiers BL, and Smit HA. 1999. Chlorsulfuran and tribenuron antagonize tralkosadim activity. South Afr J Plant and Soil 16(4):186-188.
• Tolmay VL, Van Der Westhuizen MC, and Van Deventer CS. 1999. A six week screening method for mechanisms of host plant resistance to Diuraphis noxia in wheat accessions. Euphtica 107(2):79-89.
• Tolmay VL, Van Der Westhuizen MC, and Van Deventer CS. 1999. Inheritance of resistance to Russian wheat aphid, Diuraphis noxia (Homoptera: Aphididae) in two wheat lines. South Afr J Plant and Soil 16(3):127-130.
  

UNIVERSITY OF STELLENBOSCH

Department of Genetics, Stellenbosch 7600, South Africa

G.F. Marais, F.L. Middleton, and A.S. Marais.

Breeding programs.

A triticale-breeding program for the winter rainfall region was continued. No new releases were made, but promising advanced lines were selected. Three advanced lines of Medicago polymorpha, developed in collaboration with the company Agricol, were identified for possible release. The first cycle of recurrent selection was implemented in wheat. Large numbers of selected plants could be intercrossed readily, making use of the dominant male sterility gene Ms3 and a procedure for hydroponic culture of cut tillers. Male-sterile spikes on selected plants were cut during flowering, placed in a nutrient solution, and pollinated with spikes from selected male plants. Pollen plants were discarded after 5-6 days, and the female tillers kept in hydroponic culture for another 7-8 weeks when F1 seeds could be harvested. Seed set was approximately 70 %. Integrating recurrent selection steps in a pedigree-breeding program with minimal additional input appears possible. The procedure implemented involves different selection cycles for male and female plants. F1 female plants are subjected to a single selection for seedling resistance to leaf and stem rusts (mixed inoculum of various pathotypes). In addition to F1 seedling screening, F2-F4 male families are selected in the field for disease resistance, agrotype, and quality before being used in crosses.

Genetic studies.

Following the induction of allosyndetic recombination, four Lr19-149 recombinants that resulted from proximal exchanges were recovered. Recombinant Lr19-149-299 proved to be the shortest. Another recombinant, Lr19-149-478, exchanged a translocation segment distally from Lr19, which includes the Wsp-1 locus. Plants heterozygous for recombinant translocations 299 and 478 were identified and are being test crossed in an attempt to select double recombinants.

A DH-mapping population of approximately 90 clones was developed from the F1 'Chinese Spring/PI1294994', and will be used in an attempt to map certain chromosome 7DL loci in relation to the Dn5 locus.

Attempts to find molecular markers associated with chromosomes having genes for salt tolerance were continued making use of F1 'Th. distichum/4x rye//2x rye' plants (generally having 20-22 chromosomes) and B2F2 'triticale//Th. distichum/2*triticale' derivatives. Preliminary results indicate that more than one chromosome may be involved. Eleven putative disomic additions of unknown Thinopyrum chromosomes to triticale have been derived.

Backcrosses to transfer leaf and stripe rust resistance from several Triticum species to common wheat were continued. Chromosome locations of two leaf rust resistance genes from T. turgidum subsp. dicoccoides (on chromosomes 2B and 6B) and one gene from T. timopheevii (chromosome 2B) have been determined. Further genes from these two species as well as Ae. speltoides, Ae. kotschyi, Ae. peregrina, Ae. sharonensis, and Ae. columnaris appear to have been integrated into wheat chromosomes and are being used in monosomic analyses to determine the chromosome involved.

Publication.

• Prins R and Marais GF. 1999. A genetic study of the gametocidal effect of the Lr19 translocation of common wheat. SAJ Plant Soil 16(1):10-14.