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

Development oflinear equations for predicting wheat rust epidemics - Mahir
INTRODUCTION
Stem rust ofwheat (Triticum aestivum) incited by Pucdnia graminis Per. f. sp. tritid Eriks &
Henn., and leaf rust induced by P. recondita Rob. ex. Desm. f. sp. trifid, are major wheat
production constraints in New HaIfa region, Sudan. Grain losses approaching 72%, and
kernel weight losses of up to 49.6% have been attributed to rust infections (Mohamed, 1995).
Epidemic development of stem rust can occur if disease development occurs early in the
season, around December (Mahir and Mohamed, 1997). It has been suggested that the
location of the Agricultural Production Scheme (15° - 15°15'N, 35°15' - 36° E) at the foot of
the Abyssinian Plateau confers favorable environmental conditions for rust disease
development and epidemiology. Given favorable environmental conditions and compatible
host/pathogen interactions, development and rapid progress of wheat rust epidemics are
dependent in part upon: 1) The amount of initial inoculum; 2) The effectiveness of factors
influencing size and availability of pathogen inocula (Burleigh et at., 1972). Within a 24-hour
period, concentration of airborne rust spores tended to fluctuate with wind velocity,
turbulence, dew, rain and storm fronts, as well as, periodicity in spore production
(Eversmeyer and Kramer, 1975; Gregory, 1945). Several factors affecting rust development
were studied under controlled environments (Chester, 1946).
From the author's point of view, studies on wheat rust epidemics at New HaIfa were
inadequately investigated and the results insufficiently interpreted (Mahir and Mohamed,
1997). Emphasis within ICARDA's regional programs was placed on following the seasonal
development of wheat rust diseases by the date of first appearance of uredinia in the field,
and by monitoring rust spore incidence in the ·air. Data obtained from volumetric spore
sampler were usually presented as average ,numbers of urediospores per cubic meter of air.
Except for the work reported by Mahir and Mohamed (1997), no attempt was made to
identify and quantify factors affecting urediospore incidence in the atmosphere, and ultimate
development of disease epidemics in New HaIfa.
With these considerations in mind, linear multiple regression models from biological and
meteorological data were developed to determine, if acceptable prediction was possible and,
if so, to select the most appropriate variables for the development of working models.
MATERIALS AND METHODS
The Nile Valley and Red Sea Wheat Disease Nursery (NVRSWDN98), and the Bread Wheat
Key Location Disease Nursery (KLDN99), modifications from the late Nile Valley and Red
Sea Wheat Rust Trap Nursery (NVRSWRTN), were received from the Wheat Rust Program
Coordinator, ICARDAIARC, Egypt. The nurseries consisted of newly released varieties and
advanced lines from throughout the region. A second trial representing the Sudanese National
Wheat Rust Program was received from the National Coordinator, ARC, Wad Medani,
Sudan. All trials were sown 20 th November, but received a first irrigation five days latter.
Location of trials, plot size, nitrogen fertilizer dose and application, and irrigation regime
were carried out as previously repOlied (Mahir and Mohamed, 1997).
Observations on disease development and severity, and wheat growth stage, in experimental
plots and random farmers' fields, were recorded several times each week during two
consecutive seasons, 1997/98 and 1998/99. The 1 to 5 scale wheat crop growth stage was
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