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Results and
Discussion
The wild species, Ae. variabilis, showed high resistance
to all five races of the pathogen in seedling stage, while the wheat
variety was susceptible (Table
1). DAL that
possessed a pair of alien chromosomes, expressed a moderate
resistance to powdery mildew fungus, except for 59 race. To two other
races, 59a and 111, DAL exhibited no pustules, but to 84
and 112 races it performed scant sporulation. In contrast, the wheat
parent was strongly affected by the pathogen.
As regards adult plant resistance, the difference between DAL and the
parents, was more distinguishable (Table
2). Variety
Roussalka manifested susceptibility, both on leaves and spikes, while
the wild species showed high level of resistance, but spikes were
affected by the fungus. DAL exhibited high resistance both on leaves
and spikes. In some cases, single pustules could be found on the
lowest 1-2 leaves, but to a greater extent on spikes (ear assessment
R, Table
2).
The resistance of DAL to powdery mildew fungus was due to the
presence of a pair of chromosomes, derived from Ae. variabilis.
Up to now, no information has been available as regards powdery
mildew resistance, carried by Ae. variabilis chromosomes.
Shepherd and Islam (1988) indicated the chromosome O of the same wild
species as a carrier of resistance to cereal cyst nematode, while
chromosome 6U (formerly A) of Ae. umbellulata (donor of U
genome to Ae. variabilis) as bearing resistance to leaf
rust.
Simultaneously, Ceoloni (1985), and Zeller and Heun (1985) used
chromosome G of Ae. longissima, assumed to be the second
genome donor of Ae. variabilis, to transfer powdery mildew
resistance into the genome of common wheat. Giura and Marinescu,
(1988) obtained some wheat addition lines with chromosomes of
tetraploid Aegilops species, including Ae. variabilis.
Three of those lines exhibited resistance to powdery mildew
fungus.
About 30 plants of DAL and 25 F1 hybrids of the cross DAL
x Roussalka were observed to find the mitotic chromosome number, and
all had the expected-44 and 43 chromosomes, respectively. Observation
in meiotic phases-diakinesis, metaphase I, anaphase I and tetrads led
to the conclusion that only 22-chromosome gametes had been
functioning in DAL. Consequently, the plants of DAL observed, were
meiotically stable, with normal chromosome pairing. The alien
chromosome did not carry a satellite.
Two-years field data showed that DAL had the same germination ability
as the wheat parent with white coleoptile (Table
3). Necrotic
symptom appeared in plants at shooting stage, mainly when grown in
the greenhouse. Chlorosis affected first the 2-4 leaves in all their
parts from the central to other tillers, then one or two leaves
withered and broke. This resulted in slight depression of growth that
might have been the reason for the late heading of DAL. Chlorosis on
the lowest leaves and some necrotic spots could be detected in field
conditions when compared to Roussalka wheat.
Data in Table
3 clearly
demonstrated the significant differences between the lines, when
grown on the field. DAL fully resembled wheat, but its spikes were
shorter and more compact, producing seeds with lighter grain weight
per plant than the wheat. The open fertility of DAL was
insignificantly higher in comparison to Roussalka wheat.
Data presented in this paper provide all evidence that the newly
obtained line is a stable, phenotypically distinct and crossable
aneuploid genotype of high level of resistance to wheat powdery
mildew fungus.
Literature Cited
Ceoloni C (1985) Genctica Agraria 3: 316-317
Giura A and Marinescu V (1988) Anal Inst Cerc p Cer Pl Tehn, Fundulea
56: 11-24 (In Rom.).
Iliev I (1989) Plant Science 9: 85-91 (In Bulg.).
Kimber G and Tsunewaki K (1988) Proc 7th Int Wheat Genet Symp
(Cambridge): 1209-1210.
Shepherd KW and Islam AKMR (1988) Proc 7th Int Wheat Genet Symp
(Cambridge): 1373-1381.
Zeller FJ and Heun M (1985) Theor Appl Gent 71: 513-517.
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