Abstract
Scald, caused by Rhynchosporium secalis (Oudem), is an
important disease of barley in Tunisia particularly in northern,
northwestern and central parts of the country where the climate is
usually cold and wet during most of the barley growing season.
Pathogenic variability of the barley scald pathogen in Tunisia was
determined by testing the pathogenicity of 100 isolates from 5
different regions on 19 host differentials. Pathotypic diversity was
high, with 93 R. secalis pathotypes identified on two differential sets
(one comprising 9 and the other 10 barley lines) containing known
resistance genes. A few pathotypes comprised 2% of the isolates;
however, the majorities were represented by a single isolate. None of
the differential lines was resistant to all isolates. The differential
cultivar "Astrix" was the least compatible with the scald pathotypes
followed by the differential cultivars "Atlas" and "Abyssinia".
Compatibility of the pathotypes on "Rihane" (69%) was close to that on
"Osiris" (73%) and "La Mesita"(61%). None of the pathotypes was found
in all the five regions of Tunisia surveyed. Some pathotypes were
specific to a single region while others were found in several regions.
The incidence of pathotypes varied considerably among regions, with
region 3 (northwestern Tunisia) comprising the largest number of
pathotypes. Virulent pathotypes were recovered in all regions but more
pathotypic variability (44%) was observed in the semi-arid region 3.
Differential cultivars allowed classification of R. secalis in four
virulence groups. Canonical discriminant analysis showed no apparent
association between virulence and geographical origin of the
populations. Pathogenic variability in R. secalis in Tunisia was found
not to be associated with geographical region, hence, the necessity for
deployment of different resistance sources in major barley growing
areas.