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Wheat Information
Service
Number 76:16 -19 (1993)
II.
Articles
Genes
for susceptibility to Ustilago nuda tritici in bread
wheat
V. N. Waghmare and H.C.Mathur
Division of Genetics, Indian Agricultural Research Institute, New
Delhi-110 012, India
Summary
Genetics of resistance in Chinese Spring (C. S.) to an Indian
collection of Ustilago nuda tritici was studied by using
ditelosomic and monosomic, lines. Chinese Spring was susceptible at
embryonic stage and resistant at the adult plant stage. At least
three hemizygous effective genes, causing susceptibility to U.
nuda tririci at embryonic stage in C. S., were located one
each on the long arm of chrosome 2A, 3A and 6B. Nullisomic condition
for any one of the three genes imparted resistance at the embryonic
stage to loose smut. This is the first study on genetics of
resistance to the smut at embryonic stage and also the first report
on nulli-condition resulting into resistance against loose smut.
Introduction
Loose smut (caused by Ustilago nuda tritici) is one of the
serious diseases of wheat in northern India but very little work has
been done on genetics and breeding of resistant wheat varieties
against this smut. The nature of fungal infection, difficulty in
creating artificial epiphytotic conditions and appearance of disease
in the next generation are some of the major causes responsible for
lack of genetic analysis of resistance to the smut and in hampering
breeding of resistant varieties against it. Though disease can be
contained by seed dressing with fungicides, breeding resistant
varieties remains the most economic method to reduce losses.
In order to undertake genetic analysis of loose smut, it is important
to note that floral infection is the rule for the transmission of
this disease. The smut spores (teliospores) are blown to the flowers
where they germinate and ultimately the mycelium infects embryo. This
mycelium. remains dormant in the seed. Next season when seed
germinates the mycelium gets activated and grows with the shoot tip
and causes disease at the time of ear development. In the present
experiment, genetics of resistance to the disease has been studied at
embryonic and adult plant stages which is being reported in this
paper.
Materials and methods
The plant material used in the present
study comprised of a
resistant wheat v variety, Chinese Spring and its aneuploid lines,
viz., monosomics and ditelosomics. Susceptible varieties namely, NP4,
Timagalen and Sonalika were used as checks. The inoculum used was a
mixture of unidentified isolates (collection from Northern India)
maintained on a susceptible cultivar, Sonalika.
Chinese Spring, its monosomic lines, ditelosomic lines and
susceptible cultivars including Sonalika (maintainer for inoculum)
were inoculated in 1988-1989 with the smut spores collected from
susceptible heads of Sonalika by the method described by Agrawal et
al (1963) and Mathur and Kohli (1963). Six ear heads were inoculated
repeatedly at an interval of 48 h till completion of flowering. On
maturity the inoculated seeds obtained from each ear head were
divided into two lots. One lot of seeds was used for detecting loose
smut mycelium in the embryo by "whole embryo count test" and the
other lot of seeds was sown in the field during 1989-90 to study
disease reaction at the adult plant stage.
Ten dried inoculated seeds from each ear head were tested for embryo
infection by whole embryo count test as suggesged by Mortan (1961).
The processed embryos were examined under Wild Stercobinocular
Microscope at 12, 25 and 50
x magnifications. The
presence of blue stained knotted mycelium in the embryo indicated the
loose smut infection.
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