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April 2016
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The identification of diseases
on wheat and barley grown in
the Western Cape in 2015
S
mall grain cereals are predominantly grown in the Western
Cape and more than 50% of wheat and 80% of barley grown
in South Africa, are produced in this region.
The production of grains in South Africa, however, is burdened by
economic restrains as well as various abiotic and biotic stresses.
Input costs have increased substantially due to increased fertiliser
and fuel costs, while competitive international prices have placed
additional pressure on grain production.
The most common abiotic causes for the reduction in yield and
grain quality include drought and nutrient deficiency. Biotic con-
straints include insect damage and diseases caused by viruses,
bacteria and fungi. More than 40 different genera of fungi have
been associated with diseases of grains in South Africa, including
Fusarium, Gaeumannomyces, Rhizoctonia, Puccinia
spp
., Pyre-
nophora
and
Staganospora
. Bacterial diseases are typically caused
by species and pathovars of
Pseudomonas syringae
and
Xan-
thomonas translucens
.
The most common diseases of wheat and barley are mostly iden-
tified in the field by producers, chemical representatives and con-
sultants. When unfamiliar symptoms are observed in the field,
complicating disease diagnosis, samples are often sent to the
Disease Clinic at the Department of Plant Pathology, Stellenbosch
University, for analysis.
During the 2015 growing season, 19 diseased wheat and 22 diseas-
ed barley samples (one to 20 plants per sample), from various grow-
ers in the Western Cape, were submitted to the Disease Clinic.
These samples displayed a variety of symptoms on different plant
parts, ranging from obvious root and crown rot and foliar lesions, to
more elusive disease indicators. No small grain seed batches were
received during the 2015 season, although up to 80 seed batches
per annum have been received in past years, mostly for the determi-
nation of
Fusarium
contamination.
The diseases identified by the Disease Clinic on wheat and barley
are not an indication of the incidence, or prevalence, of specific dis-
eases for the 2015 season, as these diseases only represent diseases
which are more difficult to identify in the field. For instance, rust
pathogens are more easily identified, therefore less samples with
rust diseases were submitted to the Disease Clinic for identification.
It was, however, interesting to note that more fungal species were
identified on wheat (
Graph 1
) than on barley (
Graph 2
), and that
bacteria were only found on wheat samples submitted, even though
more barley samples were received. Weaker, secondary fungal
pathogens, such as
Alternaria
,
Botrytis
and
Stemphylium
were fre-
quently isolated from wheat and barley (Graph 1 and Graph 2). Sec-
ondary bacteria, such as
Pantoea
and
Pseudomonas
, are commonly
associated with diseased and stressed plants.
Diseases / Wheat / Barley / Western Cape
ON FARM LEVEL
Integrated pest control
ILZE BEUKES, TAMMY JENSEN
and
SONJA COERTZE,
plant disease consultants:
Disease Clinic, Department of Plant Pathology, Stellenbosch University
Graph 1: Pathogenic bacteria (in shades of blue), foliar fungi (in shades of green), root and crown rot fungi (in shades of brown-
orange) and other causes associated with symptoms, identified from 19 wheat samples grown in the Western Cape in 2015.
These results are only applicable to the samples submitted to the Disease Clinic