Variation in the identification of Fusarium spp. in maize samples due to enumerator and growth medium

Abstract

Fusarium spp. have variable phenotypic and morphological features when cultured on different media. Inaccurate identifications could result in variation in the quantification of Fusarium spp. associated with ear rot of maize when two or more researchers identify the same Fusarium isolates based on morphological characteristics. Two hundred and fifty kernels from maize samples collected from each of five localities were surface-sterilized and plated on selective rose Bengal-glycerine-urea (RbGU) medium from which isolates were subsequently transferred to split plates containing Carnation Leaf Agar (CLA) and Potato Dextrose Agar (PDA) for further identification. Three different enumerators independently identified and enumerated Fusarium spp. on RbGU and CLA/ PDA media to determine the relative frequency of Fusarium spp. within maize samples, to compare the accuracy of species identification on different media and to detect and quantify bias among enumerators (inter-enumerator reliability). It was concluded that enumerators were consistent in the identification and quantification of F. verticillioides and F. subglutinans on both RbGU and CLA/PDA media. F. proliferatum enumerations yielded an interaction between locality and enumerator with no significant differences for media. The significant locality x enumerator interaction for F. proliferatum suggests that enumerators had difficulty to distinguish between F. proliferatum and F. verticillioides. The use of RbGU and/or CLA/PDA media were eliminated as a possible source of variation in the identification of Fusarium spp. The inter-enumerator reliability study indicated that Fusarium spp. enumerations by three different enumerators were reliable and accurate and were not a source of variation in the quantification of Fusarium spp. associated with maize ear rot.