Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

components individually is quite laborious and time consuming, particularly
in the case of trials with many entries. A convenient option is use of the Area
Under the Disease Progress Curve (AUDPC) technique, which takes into
account all the factors collectively leading to manifestation of slow-rusting in a
genotype. The aim of the present study was to identify slow-rusting genotypes
for stripe rust among advanced breeding material and popular cultivars grown
in different agro-climatic zones, as sources for minimizing the occurrence of
new virulence.
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Materials and methods
A trial with 114 wheat genotypes (37 advanced lines of T. aestivum, 5 advanced
lines of T. durum, and 72 checks, including 62 T. aestivum, 9 T. durum and
1 T. dicoccum) from advance varietal trial (AVT)-2nd year and 122 entries (103
lines of T. aestivum, 2 lines of triticale, 15 lines of T. durum and 2 lines of
T. dicoccum) from AVT-1st year were sown in as 1-m long rows with a spreader
row of a susceptible check (A-9-30-1) every 20th row at Karnal during crop
season 2007/08. All lines were planted as 2-m rows at 23 cm intervals in the
2008/09 crop season. Three spreader rows (row to row gap of 15 cm) of a
mixture of susceptible cultivars (A-9-30-1, Bijaga Yellow, Sonalika) were
planted on the four edges of the plot and between the test material after every
10 rows. The crop was fertilized at a rate of 120 kg N/ha (split equally between
seedling and stem elongation stages), 60 kg P/ha and 40 kg K/ha. Irrigation
was provided at crown root initiation, stem elongation, flowering and grain
formation stages of crop growth. A stripe rust epidemic was initiated by
inoculating 3-week-old plants of the spreader rows with urediniospore-water-
Tween 20 suspension having equal proportions of predominant stripe rust
pathotypes (67S8, 47S102, 46S103, 70S69, 46S119, 78S84) collected from actively
sporulating plants of susceptible varieties maintained in isolation in a
polyhouse. Hypodermic syringes and sprays were used to inoculate the
spreader rows to ensure timely establishment of stripe rust in the field. High
humidity was maintained for rust development. The infection types (Tr-R, R,
Tr-MS, MS, Tr-S and S) were recorded by following McNeal et al. (1971). Stripe
Rust scores were recorded, combining the disease severity based on the
modified Cobb’s scale and the infection type(s) of Peterson, Campbell and
Hannah (1948). The rust intensities were recorded at 10-day intervals and a
Coefficient of Infection (CI) was calculated. AUDPC values were calculated
using a computer package developed at CIMMYT, Mexico (CIMMYT, 1988).
Wheat genotypes were grouped based on AUDPC value ranges 0, 1–100, 101–
200, 201–500, 501–1000 and >1000.