Inhibition of germination and sporulation of Claviceps africana from honeydew encrusted sorghum with seed treatment fungicides

The inhibitory effects of six fungicides on macrospore germination and prod uction of secondary conidia of Claviceps africana were studied. Effects of these fungicides on germination of sorghum seed also were determined. Panic les from male-sterile sorghums with honeydew exudate were harvested from th e USDA-ARS Research Farm, Isabela, Puerto Rico in the Spring of 1997. Honey dew exudate-infested panicles were used as inoculum to infest ergot-free so rghum seed. Seeds were placed on 1 and 2% water agar containing 100 mg/l ea ch of streptomycin sulfate and ampicillin and were also plated on soil. The y were incubated at 21-22 degrees C, 16 h of light. Al 24 and 48 h, samples were examined under a microscope, equipped with 50x and 100x objectives, f or germination of macroconidia and the formation of conidiophores and secon dary conidia on both seed, soil, and agar surfaces. Samples also were evalu ated for seed germination. Abundant conidiophores with conidia were observe d over the entire seed surface of (control) honeydew-infested seed while no ne were observed on untreated control seed. Fungicidal effects and seed ger mination results showed that captan (Captan 400(R)) and thiram (42-S Thiram (R)) effectively inhibited conidiophore production and secondary conidia fo rmation without severely reducing viability of the sorghum seed. (C) 1999 E lsevier Science Ltd. All rights reserved.