Image analysis for the identification of the quarantine pest Tilletia indica*

Diagnosis of the teliospores of Tilletia indica (Karnal bunt) detected in wash tests is complicated by the fact that wheat grain can be contaminated by ‘look‐alike’ species, namely Tilletia walkeri (ryegrass bunt) and Tilletia horrida (rice smut). Although morphological diagnosis is possible when there are relatively large numbers of teliospores present, it is difficult with only a few spores as there are significant overlaps in the characteristics of each species. Molecular methods can confirm presumptive identifications, but these take 2–3 weeks. Image analysis offers the potential for more rapid confirmation. An image analysis system was developed for use on bleached spores. Bleaching spores reveals additional morphological characters (spore profile and spore wall layers) that may be used in an image analysis system to discriminate species. The image‐processing software automatically locates spores on a given image and calculates perimeter, surface area, number of spines and spine size, maximum and minimum ray radius, aspect ratio and roundness. Principal components analysis (PCA) is performed on the parameters to obtain a linear separation of spore species. Accuracy of 97% in separating T. indica and T. walkeri has been achieved in preliminary tests using PCA, but further evaluation is required.