Spore dispersal in Ophiobolus graminis and other fungi of cereal foot rots

Abstract

During Oct. 1953, air was sampled with a Hirst automatic volumetric spore trap at a height of 0·5 m. above the stubble of a wheat crop bearing fructifications of Ophiobolus graminis, Cercosporella herpotrichoides and Fusarium culmorum. Ascospores of O. graminis were never caught on rainless days; nor after rain of less than 0·01 in. They were caught within an hour of 0·01 in. or more rain and attained a maximum concentration of 3700 per m.3 of air within 2 hr. of 0·05 in. rain. Wind-tunnel tests showed that the peak rate of liberation occurred within 45 min. of wetting. All mature ascospores seemed to be discharged during 4 hr. of rain, but a few dry days sufficed for another batch to mature. C. herpotrichoides behaved differently : a few conidia occurred after a trace of rain, and more rain did not increase their numbers; their maximum concentration was only one-tenth of O. graminis. Concentrations of coloured basidiospores were more nearly constant, regardless of weather and time of day, and Cladosporium was more common by day than by night. No macroconidia of Fusarium were detected.