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Cytology and Histology

Ovarian Infection of Sporobolus poiretii by Bipolaris ravenelii. E. S. Luttrell, Department of Plant Pathology, University of Georgia, Athens 30602; Phytopathology 66:260-268. Accepted for publication 21 August 1975. DOI: 10.1094/Phyto-66-260.

False smut of Sporobolus poiretii, caused by the hyphomycetous fungus Bipolaris (Helminthosporium) ravenelii, is a local lesion disease in which infection is restricted to ovaries. Germ tubes from airborne conidia form appressoria and penetrate cells of the stigma, style, or ovary. Hyphae of the intracellular mycelium traverse host cell walls without constriction. They invaginate the host plasmalemma and become ensheathed during a brief period in which a compatible relationship exists between fungus and host. Hyphae mass within the host cells, which are soon completely absorbed. The pedicel of the floret remains green, but the ovary is replaced by a sclerotioid, pseudoparenchymatous fungus stroma. Hyphae arising from the stroma emerge between remnants of the palea and lemma and form olivaceous to black mats of long, branched conidiophores. The disease cycle may be completed in 3-4 days. Dew periods of 2-12 hours are sufficient for infection. Discoloration of the ovary is evident in 48 hours. Sporulation may occur within a minimum latent period of 60 hours, if moisture is available during the final 12 hours.