Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

23
Results and discussion
In the two years of study, yellow rust developed in most nurseries. The results
are summarized for four main regions (West, North, East and Central) of Iran,
and presented in Table 1. According to the results, virulence on Heines Kolben
(with gene Yr2), Kalyansona (Yr2), Lee (Yr7), Avocet R (YrA),
Federation*4/Kavkaz (Yr9), Yr6/6*Avocet “S”, Yr7/6*Avocet “S”,
Yr9/6*Avocet “S”, Yr17/6*Avocet “S” and TP 1295(Yr25) and YrSU was
common during those two years (Table 1).
The frequencies of virulence on plants with Yr2, Yr6, Yr7, Yr9 and YrA were
up to 70%. Virulence for Yr1 was common in Central Asia and China, rare in
most parts of the Middle East and absent in Iran (Afshari, unpublished). No
virulence was observed on plant with Yr1, Yr3, Yr4, Yr5, Yr8, Yr10, Yr15, Yr18,
Yr24, YrND, YrCV, YrSP or YrSK(27) genes in our trap nurseries. Ma and Singh
(1996) noted that Yr18 might not provide adequate protection when deployed
alone in a susceptible background. According to them, the preferred option for
achieving durable stripe rust control is to have combinations of adult plant
resistance (APR) genes giving protection approaching the levels of the most
effective seedling resistance genes.
The varieties with the Yr18 gene have remained resistant in Iran and the
gene is being used in the breeding programme in combination with other
resistance sources to obtain acceptable levels of resistance in new cultivars.
Virulence for Yr27 (Selkirk gene) was not reported from trap nurseries, but
virulence for this gene appeared in farmer's fields and was confirmed by
seedling tests in the greenhouse (Afshari, Torabi and Malihipour, 2004).
Moreover, the population of this pathotype is still limited. Virulence surveys of
pathogen populations have provided valuable information during last 10 years
and have been used in our breeding programmes.