Tg. Fetch et Bj. Steffenson, Rating scales for assessing infection responses of barley infected with Cochliobolus sativus, PLANT DIS, 83(3), 1999, pp. 213-217
Spot blotch, caused by Cochliobolus sativus, is a common foliar disease of
barley that is controlled primarily through the deployment of resistant cul
tivars. Resistance is often assessed at the seedling and adult plant stages
, but currently no comprehensive visual scale exists that describes the ful
l spectrum of infection responses (IRs) occurring on barley. From the evalu
ation of a diverse collection of barley germ plasm and C. sativus isolates,
a 1 to 9 IR scale was developed based on the type (presence of necrosis an
d chlorosis) and relative size of spot blotch lesions observed on the secon
d leaves of barley seedlings. The nine IRs were classified into three gener
al categories of low (IRs 1 to 3), intermediate (IRs 4 and 5), and high (IR
s 6 to 9) host-parasite compatibility. Low IRs consisted of minute to small
necrotic lesions with no or very slight diffuse marginal chlorosis. Interm
ediate IRs consisted of medium-sized necrotic lesions with a distinct but r
estricted chlorotic margin, while high IRs consisted of large necrotic lesi
ons with distinct chlorotic margins and varying degrees of expanding diffus
e chlorosis. In addition to the seedling IR scale, a four-class adult plant
IR scale (R = resistant, MR = moderately resistant, MS = moderately suscep
tible, and S = susceptible) was developed based again on the type and relat
ive size of lesions present on the leaves. These rating scales should be us
eful for many types of studies on spot blotch of barley.