Effect of sugary disease exudates on germination, seedling development and predisposition to seedling diseases of sorghum (Sorghum bicolor)

Abstract

Sorghum harvested for seed from Claviceps africana-infected fields becomes coated with sugary disease exudates in which the fungal spores are borne. The role of exudates in the inhibition of seed germination, seedling growth and predisposition to seedling diseases was investigated. In vitro studies showed that low exudate concentrations could reduce germination and seedling growth and that cultivars differed in their response to exudates. In the field and greenhouse, seed-borne exudate concentrations were quantified on the basis of spores g⁻¹ seed. Concentrations of 6.47 x 10⁶ spores g⁻¹ seed artificially applied to healthy seed reduced germination and seedling emergence, and predisposed seedlings to mesocotyl discoloration and post-emergence damping off. The spore concentration on seed from a naturally-infected field was 55 x 10⁶ spores g⁻¹ seed. This could be reduced by seed washing but large volumes of water were required to reduce exudate concentrations to levels which would not affect germination and seedling development.

Keywords:

• Exudates
• seedlings
• sugary disease