The Eleventh Regional Wheat Workshop For Eastern ... - Cimmyt

Performance offour new leafrust resistance genes - Temam
MATERIALS AND METHODS
Field Studies
Winter wheat accessions containing the new leaf rust resistance genes investigated in this
study are listed in Table 1. Several wheat varieties and gennplasm releases, including
Wrangler (PI477288), TAM 107 (PI495594), Karl 92 (PI564245), TAM 200 (PI578255),
Wichita (CII952), Century (PI502912), KS91WGRCI2-1, KS86WGRC2 (PI504517),
KS90WGRCIO (PI549278), KS91 WGRCII (PI566668), and S92WGRC 15 (PI566669), were
included as controls. Field nurseries were established at the Ashland experimental field,
Manhattan, Kansas during the growing seasons of 1992/93,1993/94, and 1994/95. The wheat
accessions were planted in three-row plots with 20 cm between rows. Plots were 2.7 m long
by 0.6-m wide with no border between plots. Experiments were arranged in a randomized
complete block design with four replications.
To enhance buildup of rust epidemics, test entries were inoculated unifonnly when they were
between boot and early heading stages (45-53 on Zadoks' scale) of development with a
mixture of urediniospores of different leaf rust fungal isolates collected from the Ashland
field in previous years. Three cultures of Puccinia recondite Rob. ex Desm. fsp. tritici,
CBBQ, CDBL, and MFBL were included in the rust population used to inoculate the test
entries. The avirulence/virulence fonnulae of these rust isolates are:
CBBQ = 1, 2a, 2c, 3ka, 9,11,16,17,24,26, 30/3a, 10, 18;
CDBL = 1, 2a, 2c, 3ka, 9, 11, 16, 17, 18,26, 30/3a, 10,24; and
MFBL = 2a, 2c, 3ka, 9, 11, 16, 17, 18,3011 ,.3a, 10,24,26.
These three isolates elicit a high infection type on the hexaploid parental lines involved in
producing the resistant gennplasm. Urediniospores were suspended in light-weight mineral
oil (Phillips Petroleum Company, Bartlesville, OK) and sprayed with a battery operated, fine
nozzle sprayer between 6:00 and 7:00 p.m. after dew fonnation to maintain conditions
necessary for spore gennination and infection.
Disease severity (percentage of leaf area infected by rust in each line was assessed in Kansas
twice a week between the early milk (73 on Zadoks' scale) (10) and hard dough stages (87 on
Zadoks' scale) of development using the modified Cobb scale (9). The host response to
infection was scored using "R" to indicate resistance or miniature uredinia; "MR" to show
moderate resistance that is expressed as small uredinia; "MS" to indicate moderately
susceptible, expressed as moderate-sized uredinia (smaller than the fully compatible type);
and "s" to indicate full susceptibility (9).
In Texas nurseries, single row entries of 3 m each were planted at the Texas Agricultural
Experiment Stations at Prosper and Beeville in 1994/95. These nurseries were exposed to
natural infection. Rust severity estimations were made at watery ripe to milky developmental
stages (71-77 on Zadoks' scale).
Growth Chamber Studies
Seedlings of the four accessions with new leaf rust resistance genes along with parental lines
and susceptible checks were tested twice in 12, 16, 20, and 24°C environments. The leaf rust
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