Rating scales for assessing infection responses of barley infected with Cochliobolus sativus

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.