Taxonomy of Fusarium fujikuroi species complex associated with bakanae on rice in Korea

Abstract

Bakanae occurs throughout rice growing regions of the world including Asia, Africa, America and Europe. So far the pathogen causing bakanae on rice has been widely known as F. fujikuroi in the Korean peninsula. However, previous studies have shown that Fusarium species within the Gibberella fujikuroi species complex are commonly associated with bakanae. Therefore the objective of this study is to determine the genetic diversity of the Fusarium species responsible for bakanae. Using morphological approaches and translation of DNA sequences belonging to elongation factor 1 α (TEF), histone H3 and calmodulin genes, the pathogen was identified and characterized. A total 590 isolates of Fusarium species were recovered from the rice plants with typical symptoms of bakanae and rice seeds. Out of one set of the 100 Fusarium isolates, the phylogenetic tree of 90 isolates amplified and constructed from DNA sequences of TEF gene consisted of three main clades. Futher it was observed that of the 89 Fusarium isolates amplified and constructed from 474 bp of DNA sequences of histone H3 gene, consisted of F. fujikuroi and F. proliferatum groups. Lastly, based on DNA sequences of clamodulin gene, 89 isolates including F. fujikuroi and F. proliferatum formed one clade with each reference strain. It could be again sub divided into F. proliferatum group and 2 F. fujikuroi groups. As clearly demonstrated in this study, identifying Fusarium species associated with bakanae only depending on morphological investigation is a highly challenging task, owing to its diverse characteristics. Moreover, other Fusarium species such as F. proliferatum, and F. andiyazi besides F. fujikuroi are also capable of causing bakanae. And also besides these there are other non-pathogenic F. fujikuroi which are hard to distinguish even with molecular identification protocols.