A rapid method of counting spores of fungal pathogens by infra‐red reflectance analysis

Abstract

A method of counting freshly harvested spores of powdery mildew (Erysiphe graminis f.sp. hordei), yellow rust (Puccinia striiformis) and brown rust (P. hordei) of barley as well as brown rust (P. recondita) of wheat, using infra‐red reflectance spectrophotometry was investigated. A Neotec 6350 Research Composition Analyser was used to scan spore samples on glass‐fibre filter disks in the near infra‐red region of the spectrum (1100–2500 nm) and the amount of energy reflected at 1400 different wavelengths recorded. Three wavelengths (1900, 2252 and 2308 nm) that together gave the best multiple correlation with spore populations counted on a haemocytometer slide were selected. Partial regression coefficients for each fungal species were derived by relating reflectance energy values to direct spore counts. Utilizing these and the energy reflected at the three selected wavelengths, it was possible to count spore samples with high precision. Correlations >0.9 between numbers estimated by the instrument and those obtained using a haemocytometer slide (within the range 0–30000 spores) were achieved with all the fungi examined. Application of the technique to smaller, fixed‐filter instruments as a routine method of counting spores is discussed.