Distinguishing the species - CIMMYT

Septoria leaf blotch of barley
Septaria passerinii
Leaf blotch of barley, caused by S. passerinii,
appears to be restricted to cultivated barley and
some of its wild relatives. The disease is common in
the northern area of North America, Eu rope and
Asia, but it is the least damaging of the septoria
complex.
The leaf blotch symptoms are similar to those
produced by S. avenae, including the dark specks
(embedded pycnidia - see Figure 77). Septaria
species that are pathogenic on barley produce dark
pycnidia in the lesions, thus microscopic examination
is necessary for accurate identification.
Figure 77. Typical leaf blotch symptoms on barley, caused
by S. passerinii.
Colonies of dark brown pycnidia develop in
the elongated lesions on leaf blades, leaf sheaths,
and stems (Figure 78). The conidia are hyaline, and
may be straight or curved, with one end tapering
slightly more than the other. They measure 26-42
11m x 1.5-2.0 11m and usually have three septa
(Figure 79). The fungus has been observed in the
leaf and stem lesions of mature barley grown on
the High Plateau of Mexico. These conidia are
sometimes curved, and may exceed 2.0 11m in width
(Figure 80).
The fungus persists in plant debris, particularly
on the dead leaves of Hordeum jubatum or other
wild barleys that are common in areas where this
disease occurs. Little attention has been given to
the development of resistant varieties and other
disease control measures.
Figure 79. Typical conidia of S. passerinii (10 x 40).
Figure 78. A close look at S. passerinii pycnidia on diseased Figure 80. Somewhat different conid ia of S. passerinii taken
barley. from diseased barley on the High Plateau of Mexico (10 x 40).
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