Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

Breeding for yellow rust-resistant varieties should be regarded as the only
long-term remedy to protect the crop from the disease. The objective of the
programme reported here was to develop and screen wheat germplasm
against yellow rust under natural and high-stress inoculation conditions, to
monitor the lines that might have minor-gene-based resistance, and to transfer
that resistance to susceptible but high yielding, adapted varieties through
conventional hybridization, for the development of wheat varieties having
minor-gene-based resistance against yellow rust.
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Materials and methods
A programme for breeding for yellow rust resistance was initiated at the
Wheat Research Institute, Faisalabad, Pakistan, during 1992/93. Wheat
germplasm comprising 140 lines were screened for yellow rust resistance
under natural conditions at Islamabad, Pirsabak, Peshawar and Kaghan, and
under artificial inoculated conditions with diversified inoculum at Faisalabad.
All the entries were sown in two 2-m long rows at 30 cm intervals with a
susceptible check, cv. Morocco, after each ten entries. The material was planted
on two sowing dates one month apart at Faisalabad to provide a maximum
period of exposure under rust conditions for all growth stages. The nursery
was inoculated with yellow rust races in the second week of January. Rust
reaction was recorded when the susceptible check was 100S. The lines showing
a slow-rusting tendency with a 20–40% terminal rust rating were marked for
the crossing programme on the assumption that these might have minor-gene
resistance. These parents were crossed with local adapted high yielding
varieties. Twenty single crosses were developed in 1994–95, while in the next
season 30 three-way crosses were developed by crossing the F 1 with either of
the recurrent parents or a third parent. The material was advanced by using
the selected-bulk approach (Singh, Huerta-Espino and William, 2005) and
disease pressure in segregating populations was created by inoculating the
susceptible border rows with diverse races of yellow rust. Plants having rust
reactions up to 30MR were tagged from each cross in the F 2 to F 5 generations.
From the F 5 generation , single-head rows were raised from desirable selected
plants having 90–110 cm plant height, 10–30 tillers/plant, compact head, 50–
90 grains/head and with amber grain colour. Similarly, from the F 6 head rows,
selections were again made based on the same criteria together with low
terminal rust rating. The selected F 6 rows were harvested and allotted entry
numbers and were put in preliminary yield testing trials. The best were tested
in micro-yield trials and national uniform yield trials in different agroecological
regions of the country. These entries were also tested in disease
screening nurseries in hot-spot areas for yellow rusts (Islamabad, Pirsabak-
Nowshera, Peshawar and Kaghan). The data for disease resistance were
recorded following Roelfs, Singh and Saari (1992).