Resistance to Mycosphaerella graminicola causal agent of Septoria trit
ici blotch, was identified in progenies of crosses with European winte
r wheat cultivars, Tadorna and Cleo. This resistance was used to devel
op the resistant spring wheat cultivar Tadinia, selected from 'Tadorna
'/'Inia 66', released in 1985. Evaluation of the progeny of intercross
es between 'Tadorna', 'Cleo', 'Tadinia', and two short-statured resist
ant lines derived from hybrids with 'Tadinia' as one parent indicate t
he resistance was inherited as a single gene showing partial to strong
dominance. The gene in 'Tadinia' was designated Stb4. Crosses between
another resistant cultivar, 'Bulgaria 88', and 'Tadinia' suggest that
'Bulgaria 88' does not have Stb4. Successful introgression of Stb4 in
to RhtI + Rht2 short-statured lines revealed that plant stature and re
sistance to M. graminicola segregated independently. The Stb4 gene has
been effective since 1975 against M. graminicola extant in California
. A high positive correlation between seedling and adult plant disease
scores, based on scoring of lesions producing pycnidia, indicated tha
t the Stb4 gene is expressed throughout the life cycle under both fiel
d and greenhouse conditions, confirming that disease screening can be
carried out on seedling plants. Separate assessment of necrotic lesion
s with and without pycnidia indicated that leaf necrosis without pycni
dia, observed, especially under greenhouse conditions, can confound di
sease evaluations and lead to inaccurate genotype classification.