Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

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Introduction
Yellow rust (Puccinia striiformis f.sp. tritici) caused substantial losses of wheat
production in some major wheat growing areas of Morocco in 2009, due to
rapid systemic infection of affected plants resulting in defoliation and shrived
kernels. This is primarily a disease of cool climates. In Morocco, it had
occurred in continental areas, without causing major losses. However,
outbreaks of yellow rust have been reported in the past in the neighbouring
countries in western Mediterranean. Thus, serious attacks of the disease
occurred in Portugal in 1957 and 1960 (Zadoks, 1965), in Spain in 1957, 1960
and 1978 (Zadoks, 1965; Nagarajan et al., 1984), and in Italy, Tunisia and
eastern Algeria in 1977 (Ghodbane, 1977; Vallega and Zitelli, 1979). A recent
epidemic of yellow rust was reported in Algeria in 2004, but not documented.
The outbreak of yellow rust could be attributed to favourable climatic
conditions for disease onset and spread, to the widespread adoption of
susceptible cultivars and the presence of virulent pathotypes (Zadoks and
Bouwman, 1985). The objective of this paper is to analyse the components of
the epidemic (climate, host and pathogen) that had occurred in the growing
season 2008/09 in yellow rust-prone areas and to assess its impact on wheat
production.
Materials and methods
Disease survey
Field trips were organized to locate yellow rust foci and to assess the
subsequent disease development. There were four surveys: 12–13 March, 27–28
April, 15 May and 13 June. The areas surveyed were the Sais plains and the
Middle Atlas Mountains. Stops were made each 20 to 30 km. At each stop we
recorded the location (using GPS), the cultivar, the growth stage and disease
severity (percentage of leaf area infected). An estimate was made each time on
the potential yield and predicted yield loss.
Experimental yield loss estimation
A fungicide trial was conducted to determine potential yield loss caused by
yellow rust. We compared one and two fungicide applications in addition to
the control. The plot size was 50×12 m. The widely grown susceptible cv.
Achtar was used. The fungicide was applied when the first yellow rust foci
were observed on a neighbouring field, and the wheat was at the two-node
growth stage. Opus (epoxiconazole) was sprayed at the rate of 1 L/ha on 26
February 2009. The second fungicide application took place four weeks later, at
heading stage. Disease severity data were recorded each week after the first
fungicide application. Yield components were determined at harvest in May.