CHLOROSIS OF SEQUENTIALLY OLDER LEAVES OF POA PRATENSIS INDUCED BY BIOLOGICALLY-ACTIVE PRODUCTS OF BIPOLARIS-SOROKINIANA

Research was initiated to develop a rapid assay for determining the ab ility of biologically active products of Bipolaris sorokiniana to indu ced chlorosis in intact (not detached) leaf blades of Poa pratensis, a nd to determine if the active products interact with leaf senescence. The presence of membrane disrupting substances in the extract was conf irmed by the leakage of betacyanin from red beet root cells. The non-d iluted extract induced severe leaf chlorosis in leaves of all ages. At dilutions of 10(-1) and 10(-2), the youngest leaf blade remained visi bly green, and the second leaf blade showed mild chlorosis. The third and fourth (oldest) leaf blades showed severe chlorosis in response to the 10(-1) dilution, and chlorosis occurred on about one-half the len gth of the leaf blades in response to the 10(-2) dilution. Chlorosis o f treated leaf blades developed slowly and toward the tip end of the l eaf. Severely chlorotic leaves often developed necrotic flecks and/or necrotic midvein streaks. It was concluded that the extract from B. so rokiniana induces chlorosis, interacts with leaf senescence, and conta ins substances active in pathogenesis.