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 ability of biologically active products of Bipolaris .sorokiniana to induced chlorosis in intact (not detached) leaf blades of Poa pratensis, and to determine if the active products interact with leaf senescence. The presence of membrane disrupting substances in the extract was confirmed by the leakage of betacyanin from red beet root cells. The non-diluted extract induced severe leaf chlorosis in leaves of all ages. At dilutions of 10"ʹ and 10 -, the youngest leaf blade remained visibly green, and the second leaf blade showed mild chlorosis. The third and fourth (oldest) leaf blades showed severe chlorosis in response to the 10~ʹ dilution, and chlorosis occurred on about one-half the length of the leaf blades in response to the 10"^ dilution. Chlorosis of treated leaf blades developed slowly and toward the tip end of the leaf. Severely chlorotic leaves often developed necrotic flecks and/or necrotic midvein streaks. It was concluded that .the extract from B. sorokiniana induces chlorosis, interacts with leaf senescence, and contains substances active in pathogenesis