Atypical, green leaf blotch lesions on barley leaves infected by Rhynchosporium secalis (Oud.) Davis

Atypical, green leaf blotch lesions were observed on senescent leaves in winter barley crops and sometimes developed on barley leaves inoculated with conidia of Rhynchosporium secalis in a glasshouse. Similar atypical lesions were induced on barley leaves inoculated with conidia of R. secalis and then grown in controlled environments at 10 degrees C and 80% rh. Microscopic examination of green lesions from these three sources showed that hyphae of R. secalis had colonized the subsidiary cells of stomata so that guard cells were swollen, resulting in enlarged stomatal pores. Additionally, spore initials had erupted through the leaf cuticle of some leaves. Most spore initials did not develop into mature conidia when leaves were incubated for 24 h at 20 degrees C in a closed chamber at 100% rh, but aerial hyphae grew out from the leaf surface. Thus, atypical green lesions produced a much smaller number of spores than typical leaf blotch lesions.