Abstract :
Elicitor-active glucan was applied to leaves of genotypes
of barley expressing different levels of resistance to powdery
mildew (Erysiphe graminis f,sp, hordei) which was
assessed by measuring mildew colonies per leaf or speed
of papilla induction response to mildew challenge. The
influence of humidity was also assessed by treating leaves
with glucan, inoculating with mildew and imtnediately
sealing the leaves in Perspex containers in an apparatus
which enabled temperature, air speed and humidity to
be controlled accurately. In water-treated controls low
humidity alone reduced colonies per leaf, and at 60% r,h,
genotype 7204 showed significantly less effect of humidity
compared with other genotypes, although at 40% it
responded as other genotypes. At low humidity glucan
stimulated resistance for genotypes Proctor and 7204 but
not for Golden Promise or 9855; the effect of humidity
or elicitor alone was only significant on genotype 7204,
Chitin also proved an effective elicitor, but at high and
not at low humidity. Time of pre-treatment before mildew
challenge, leaf stage, type of elicitor, concentration of
elicitor, post-inoculation light regime, mildew isolate and
barley genotype all had major influences on papilla
response. Other factors were less important. Based on
papilla formation, the barley cultivar Proctor was most
and Golden Promise the least responsive to glucan as an
elicitor. The potential for exploiting the genetic basis of
inducible resistance is discussed
