Sunlight and viability of cereal rust uredospores

Abstract

Uredospores (urediniospores) of Puccinia striiformis West., P. graminis Pers. f.sp. tritici Eriks. & Henn. and P. recondita Rob. & Desm. f.sp. tritici Eriks. & Henn. were exposed to sunlight on cooled supporting surfaces at ground level, while control spores were held in shade at similar temperatures. Spores in shade remained highly germinable for the duration of the exposures. About 20 h exposure to sunlight on relatively clear days in midsummer in England reduced germinability of P. graminis uredospores to 10% whilst 6–10 h caused a similar reduction in germinability of uredospores of P. striiformis. Sparse data for P. recondita indicate its uredospores to be about two-thirds as resistant as those of P. graminis. Exposure for a complete day in relatively sunny conditions reduced the germinability of P. striiformis uredospores to less than 0·1%. Experiments with short-wave cut-off filters suggested that solar energy in wavelengths close to 300 nm was only partly responsible for inactivation; wavelengths within the 315–400 nm band were also involved. It is concluded that the detrimental effect of solar radiation on longdistance uredospore dispersal, although variable, is likely to be significant on certain occasions, particularly for P. striiformis.