Bipolaris halepense: A New Species from Sorghum halepense (Johnsongrass)

Abstract

Bipolaris halepense sp. nov. from diseased leaves of johnsongrass (Sorghum halepense) in North Carolina is described. On leaves of susceptible johnsongrass plants, B. halepense induces ovate lesions 5-10 x 2-4 mm with straw-colored centers and dark-pigmented margins. Conidia of B. halepense are larger than those of B. sorghicola, which is a common foliar pathogen of Sorghum spp., and B. halepense has a much broader host range than B. sorghicola. In addition, the lesions of B. halepense on leaves of johnsongrass generally lack the zonate pattern typical of B. sorghicola lesions on johnsongrass. Morphologically, conidia of B. halepense most resemble those of B. maydis, a foliar pathogen of corn (Zea mays), but B. halepense is only weakly pathogenic to corn and did not mate with fertile isolates of either mating type of B. maydis. Bipolaris halepense induced lesions on numerous monocot and dicot plants in greenhouse tests, but failed to sporulate on detached leaves of dicots tested, or several of the monocots. Bipolaris halepense sporulated in lesions on detached leaves of johnsongrass with 24 h incubation at high relative humidity and on detached leaves of sorghum (Sorghum vulgare) and sundangrass (S. sudanense) within 48 h.