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Bread wheat cultivars carrying Sr24 and Lr24 are widely
grown in Australia, North America and South Africa. In India too,
three cultivars viz., Vidisha, Vaishali and HW 2004 (C 306*7/TR
380-14*7/ 3Ag#14), carrying Sr24 and Lr24 have been
released commercially in recent years. Backcross line HW 2004 has
been released for cultivation under dryland conditions of Central
India. This backcross line has yielded significantly higher than that
of its recurrent parent C 306, particularly under high incidence of
leaf rust. The plains of Central India are the route of migration of
stem rust and leaf rust uredospores to the main wheat belt of
northern plains. Since the rainfed crop in central plains is early
sown, the inoculum built up on susceptible cultivars poses a major
threat to the timely and late sown crop of central and northern
plains. To cheek rust infection in this secondary source, cultivation
of HW 2004 is the only economic and effective answer. Sawhney and
Goel (1983) reported that Lr24 conferred effective seedling
resistance to all prevalent and virulent leaf rust pathotypes in
India. Though virulences for Lr24 have been reported from
North America (Gough and Merkle 1971; Long and Kolmer 1989), South
America (Singh 1991) and South Africa (Pretorius et al. 1990), this
gene is still very effective in India.
The authors observed that the chromosome segment with Sr24
and Lr24 enhanced resistance to Barley Yellow Dwarf Virus
(BYDV) in backcross lines, Kalyansona*6/TR 380-14*7/3Ag#14, HD
2329*7/ TR 380- 14*7/3Ag#14 and WL 711*7/TR 380-14*7/3Ag#14. The
recurrent parents viz. , Kalyansona, HD 2329 and WL 711 are
susceptible to BYDV. This disease is the most widely distributed
viral disease on cereals and can cause serious economic losses
(Zillinsky 1983); wheat, barley, oats, rye, triticale and grasses are
hosts of BYDV. Affected plants were stunted (reduced height, short
leaves with excessive tillering and had pale yellow leaves, most of
the spikes were sterile and had delayed anthesis). The frequency of
BYDV affected plants was 12-18% in HD 2329, Kalyansona and WL 711
compared to backcross lines carrying Sr24-Lr24 (2-3%)
(Table 3). Variability for resistance to
BYDV seems to be scanty among wheat germplasm (Fedak 1998) and must
be sought in tertiary gene pool. Cultivar Sonalika identified as
resistant in present study should be screened at multilocation where
BYDV infection is ensured. The authors also observed varying degree
of terminal clubbiness of spikes which seems to be associated with
the resistance imparted by Sr24 and Lr24; however,
cultivars with least or minimum clubbiness were selected to eliminate
the risk of shattering of seeds in the final variety constituted.
Acknowledgments
The authors express their deep gratitude to Drs. R.N. Sawhney,
Indian Agricultural Research Institute, New Delhi, India (now
superannuated) and R. A. McIntosh, Plant Breeding Institute,
University of Sydney, Australia for the supply of donor used in the
present study. Our grateful thanks are also due to Mr. S. Bojan for
providing technical assistance.
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