SMALL GRAIN INSTITUTE
Private Bag X29, Bethlehem 9700, South Africa.
Winter wheat breeding.
H.A. van Niekerk, H. Knobel, N. Warburton, A. Malan, D.J. Exley, O. Muller, B. Wentzel, L Kruger, and R. Pretorius.
Two new cultivars with Russian wheat aphid resistance,
`Gariep' and `Limpopo' were
released during the 1994ñ95 season and will be available
commercially during the 1997ñ98 season. These are intermediate
types with exceptionally good bread baking quality. These cultivars
are high-producing, widely adapted, stable cultivars for the dryland
conditions in the summer rainfall region of South Africa, which
is responsible for 60 % of the total wheat production in the country.
An aluminium tolerance program was initiated to
improve the level in all cultivars and assist in the production
of `widely adapted' cultivars. Aluminium tolerance
was identified as an important selection criterion and will be
studied using a laboratory seedling test and field evaluations
on aluminium-toxic soil. In addition, the level of Al tolerance
in all crossing parents will be increased using a backcross program.
Our shuttle program between South Africa and Turkey
(CIMMYT) has benefited our program, continues to do so, and has
enabled us to make a total switch to RWA-resistance cultivars
in the shortest possible time.
The molecular biology laboratory currently is using
the RAPD technique to screen a number of genotypes for molecular
markers linked to traits of interest, especially RWA resistance,
sprouting resistance, and Al tolerance.
Olaf Muller replaced Wayne Miles in the Oats and
Triticale Program. Barend Wentzel joined the molecular biology
laboratory from the quality laboratory and Liesel Kruger completed
her Technicon training year and was appointed as a technician
in the Molecular Biology laboratory.
H.A. van Niekerk, F. Koekemoer, A. de Villiers, T.G. Paxton, S. Jordaan, R Britz, F. Groenenwald, and S. Pelser.
The primary objective of the spring wheat breeding
programs is to release commercial cultivars for irrigated and
rainfed dryland conditions. The secondary objective is to develop
RWA-resistant spring wheat cultivars for the eastern Free State
area, which can be grown as a summer wheat crop. Regarding the
latter, five single-replicated junior trials with 66 entries were
evaluated. Two lines will be presented for provisional release
in the irrigated areas, namely BSP 94/3 and BSP 94/17. The cultivar
Marico is more popular among the farmers in the warmer irrigated
areas because of its resistance to lodging, whereas Kariega's
popularity is restricted to the cooler irrigated areas.
Hugo van Niekerk was nominated as the South African
representative to the Maize and Wheat Steering Committee of the
SADC (South African Developement Community). The leader of this
group is Dr. Thomas Payne of CIMMYT who is based in Harare, Zimbabwe.
The portion of the spring wheat program aimed at
the rainfed production areas still has the increasing of protein
content as its major objective. BC1-derived lines with the high
protein genes from T. dicoccoides will be submitted for
agronomic evaluation during the 1996 season.
Anri de Villiers joined the program as a replacement
for Anshen Grobbelaar.
International nurseries and germplasm bank.
I.B.J. Smit, T. Bredenkamp, and A. Otto.
The international nurseries are important components
of the breeding program, which continues to provide valuable information
about new germplasm. We evaluated 2,134 new wheat genotypes,
497 barley genotypes, and 202 triticale genotypes, which came
from Mexico, the United States, and Turkey. From these, 624 wheat
genotypes were selected for further evaluation and inclusion in
the germplasm bank.
The germplasm bank, which ensures that germplasm
is effectively used, stored, and freely exchanged, requested seed
and supplied seed internally, nationally, and internationally.
Selected wheat species were multiplied during the year in an
intensive process in tunnels. The germplasm bank is being run
according to the National Genebank policy as prescribed by the
secretariat of the Genetic Resources: Technical Task Team (Plant
Production)
I.B.J. Smit (Smitty) retired from the Small Grain
Institute on the 29th of February, 1996, after 24 years of service.
He has done invaluable work in the evaluation of international
germplasm for adaption to South African conditions.
J. Purchase, S. Ybema, A. Barnard, F. Bruin, H. Potgieter, T. Walsh, H. Hatting, A. Botha, C. Nel, M. Maritz, B. van Rensburg, and M. van der Merwe.
General crop conditions.
The Western Cape experienced a most favorable season with a near-record
wheat crop and a record barley crop. Dryland wheat in the Free
State produced average yields, but of rather poor quality because
of low bushel weights and fairly widespread preharvest sprouting.
Under irrigated conditions (25 % of national crop) fairly good
yields were achieved, but extensive frost damage along the Orange
River producing area caused major crop losses. An average national
crop of approximately 2.25 million tons is expected, which just
about meets the country's demand.
Cultivar evaluation.
In the Western Cape, experimental results and Wheat Board Statistics
indicate that `Palmiet' (released in 1983) remains
the principal cultivar in this region and accounted for the majority
of production in the Western Cape. This performance was followed
closely by the cultivars Nantes and Adam Tas (1989). However,
of the two recently released cultivars SST38 and SST55 (1993),
only SST55 produced comparable yields. According to experimental
results, this cultivar is better adapted to conditions in the
Western parts of the region (Swartland). The new generation of
RWA-resistant cultivars for the Free State is now available on
the market, and these cultivars will have a marked and significant
effect on production there (± 50 % of country's production).
Results from this program indicate general yield increases of
approximately 10 % on the susceptible varieties, and improved
quality in terms of bushel weight. Various new cultivars, SST825,
Kariega, Marico, and others, also are now available under irrigated
conditions. All released cultivars from all breeding institutions
are evaluated on an objective basis, and the results, analyzed
using AMMI, are available to farmers and other interested parties.
Outreach to Africa. The
Crop Science Division of Small Grain Institute will distribute
the SADC Wheat Yield Nursery to all member countries of the Southern
African Development Community (SADC) and to Ethiopia and Kenya
starting in 1996. This cooperative program has the objective
of distributing the best released cultivars in the different countries
to member countries for evaluation, possible release, and perhaps
commercial production. This program is conducted in very close
cooperation with CIMMYT and funded by the European Union.
Seed physiology. An accredited
seed laboratory was established and two seed physiologists, Dr.
Sierk Ybema, formerly of the Wheat Board, and M.Sc. Federika Bruin
of Margaretha Mes Seed Institute, were appointed to the laboratory.
Research contracts already are closed, and seed services are
being supplied on a commercial basis.
Preharvest sprouting. The
major objective in preharvest sprouting research is to solve the
practical problems faced by the cereal producers and the cereal
industry in general. In maize, preharvest sprouting was shown
to be exacerbated by a molybdenum deficiency. Also well-known
is that the lack of molybdenum occurs mainly in acid soils. Because
of the widespread incidence of acid soils in the major wheat-producing
regions of South Africa, a study was undertaken to investigate
the possible association between the acidity of the soil and susceptibility
of wheat genotypes to preharvest sprouting. Preliminary studies
indicate that certain cultivars, specifically those with moderate
resistance to preharvest sprouting, are less likely to sprout
when a liming program is implemented.
B.D. van Niekerk.
Leaf rust (Puccinia recondita
f. sp. tritici). Although
no leaf rust epidemics were reported in commercial fields, breeding
trials, or trap nurseries, the Swartland area in particular was
infected heavily during the 1995ñ96 wheat production season.
Also notable were the high infection of wheat in Natal and wheat
planted late in the Eastern Free Sate. Leaf rust samples were
collected during the annual rust survey are being processed currently.
The following pathotypes were recovered during the 1994ñ95
rust survey: 3SA122, 3SA129, 3SA132, 3SA133, 3SA134, 3SA137,
3SA140, and 3SA141. The season was dominated by three pathotypes,
namely 3SA132 (29 %), 3SA140 (20 %), and 3SA133 (20 %), whereas
3SA137 (14 %) was present to a lesser extent. This represents
no shift in virulence and can be explained by the virulence to
Lr24. Pathotypes 3SA132, 3SA133, and 3SA140 are virulent
on the cultivar Palmiet (Lr24), which makes up approximately
60 % of the Western Cape production, the latter being responsible
for most of the samples. Pathotypes 3SA137 and 3SA140 (virulent
to Lr24) possess virulence to Lr26, whereas 3SA133
also possesses virulence to Lr20. Although this was the
pattern for the last 6 years, it can be expected to change with
a declinine in the production of the cultivar Palmiet (Lr24)
and an increase in production of cultivars with other resistance
genes.
G.J. Prinsloo, V.L. Tolmay, J.L. Hatting, and R. Mare.
The inheritance and mechanisms of resistance in two
RWA-resistant lines was determined. Both the lines OSU ID 2808
and Aus 22498 contain single dominant genes, but it is not know
whether they differ from each other or not. The predominant mechanism
of resistance in the line OSU ID 2808 is antibiosis and a low
level of antixenosis may be present. The predominant mechanisms
of resistance in the line Aus 22498 appear to be tolerance and
antibiosis. A low level of antixenosis also may be present.
Acceptable levels of RWA resistance are being maintained
in the SGI winter and intermediate breeding programs, and the
backcross program is progressing well. Problems were experienced
with an entomopathogenic fungus in the RWA colony, which all but
closed down research projects from July to November, when the
problem was solved.
A field trial of seven resistant and three susceptible
cultivars was performed to determine the influence of insecticidal
control of RWA on yield.
Two fungal pathogen species were isolated successfully
from the Russian wheat aphid (Diuraphis noxia) cultured
on Sabouraud dextrose agar to which 1 % yeast extract was added.
Fungal cultures were maintained at 23 C and a 16-hour photoperiod.
Samples of both fungi were shipped to Dr. R.A. Humber, an insect
pathologist with the USDA-ARS, Ithaca, NY, USA, for identification.
To date, one of the species has been identified as Conidiobolus
thromboides (Entomophthorales: Ancylistaceae). Confirmed
identification of the second species is expected early in 1996.
Various methods for long-term storage of these fungi
were investigated during 1995. Two methods were tested: (1)
storage in -80_C freezers (in cryogenic vials containing filter-sterilized
10 % glycerol into which small blocks of the culture were placed)
and (2) storage of cultures in sterilized liquid paraffin at 15_C.
Viability tests after 4 months indicated better regrowth from
samples of both species stored in the freezers than from those
stored in liquid paraffin.
Practical issues in terms of disease management
during mass rearing of D. noxia also were considered. Sanitation
was found to be of critical importance in such a rearing protocol.
All cages, pots, and rearing equipment were washed periodically
with a 5 % hypochloric solution to eliminate any sources of inoculum.
Wheat seeds were surface sterilized (70 % ethanol for 30 seconds
and 5 % hypochlorite for 60 seconds, then washed in sterilized
distilled water) and planted in sterilized soil. Watering of
plants was restricted to twice per week in order to maintain relative
humidity levels of less than 50 % within the rearing cages.