Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

variation for yellow rust resistance exists among wheat cultivars (Anpilogova
and Levashova, 1995; Pasquini et al., 1998). Several studies (Cetin, Dusunceli
and Albustan, 1998; Dusunceli et al., 1998; Khan et al., 1998; Hussain et al., 1999;
Pasquini et al., 1998) have been conducted to determine reaction of wheat
genotypes, which have been variously classified as resistant, moderately
resistant, moderately susceptible or and susceptible to yellow rust (Pasquini et
al., 1998). Khan et al. (1998) also reported that wheat lines or cultivars tend to
rust faster under favourable environmental conditions. As the appearance of
new races of yellow rust poses a continuing threat, there is an urgent need to
identify new sources of yellow rust resistance from the wheat gene pool.
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Materials and methods
Plant material and sowing
Bakhtawar 92 was tested in the Trap Nursery during 1999–2000 and was
incorporated in the National Wheat Disease Screening Nursery (NWDSN) in
2001/02 and 2002/03. The Trap Nursery comprised 110 entries, whereas
NWDSN consisted of 468 and 432 entries, respectively. The Trap Nursery was
sown at 15 locations, whereas NWDSN was planted at 11 sites throughout
Pakistan. In each nursery, entries were planted in single 1-m-long rows and
30 cm apart. Two rows of varieties Local White, Morocco and Sonora, which
are susceptible to wheat rust, were planted around the nursery.
Additional field experiments were conducted under irrigated conditions at
NIFA from 1996 to 2000 and included two nurseries: the International Bread
Wheat Screening Nursery (IBWSN) and Semi-Arid Wheat Screening Nursery
(SAWSN), which originated from CIMMYT (Mexico). In the five seasons 1996–
2000, SAWSN consisted of 291, 283, 205, 174 and 166 entries each year,
respectively. The IBWSN consisted of 493, 445, 265 and 276 genotypes each
year, except 1997–98 when it was not tested. During each cropping cycle both
nurseries were separately planted in strips of small adjacent plots with 2 rows
per plot of 2.5 m length separated by 0.3 m. A susceptible wheat cultivar (Local
White) was sown around each nursery as spreader, and also served as an adult
plant susceptible check.
Development of yellow rust epiphytotics
Artificial inoculation with a mixture of field-collected bulk inoculum of known
prevalent races of the pathogen was carried out in February–March each year.
Initial inoculation of spreaders involved inoculating 3 to 5 tillers in a row, with
a hypodermic syringe containing aqueous urediospore suspension to which 1–
2 drops of Tween-20 were added in order to break surface tension.
Subsequently, all material was spray inoculated 2–3 times at fortnightly
intervals using a turbo-air sprayer to provide an aqueous spore suspension
conducive to heavy rust development.