Population genetic analysis of Fusarium circinatum in Colombia and Chile

Abstract

Fusarium circinatum is a fungal pathogen of Pinus species. The fungus causes a disease known as pine pitch canker on Pinus species. The emergence of Fusarium circinatum as a significant threat to Pinus species in commercial forestry worldwide sparked extensive research into its biology, ecology, and epidemiology. Despite considerable progress in understanding its global population biology and genetic diversity, a gap in knowledge regarding its populations in South America became apparent. Especially with reports of both mating types. This led to a focused investigation into the population biology of F. circinatum in two South American countries, Chile and Colombia. In Colombia, the study revealed a clonal population predominantly composed of 116 MAT 1-1 isolates, indicating limited genetic diversity. Moreover, comparisons between historical nursery samples and more recent field isolates suggested minimal differentiation over time, implying persistent gene flow within the population. Interestingly, the population structure analysis hinted at three distinct introductions of the pathogen into the country. Similarly, in Chile, the population exhibited a clonal nature, with only the MAT 1-2 mating type identified among the 71 nursery isolates. The population structure analysis pointed to two separate sources of inoculum introduction of the pathogen. Notably, low differentiation levels and substantial gene flow were observed among nurseries, indicating the simultaneous spread of a few dominant clones between and within the different nurseries. These findings underscore the widespread and persistent threat posed by Fusarium circinatum to pine forests. By enhancing our understanding of its population dynamics, this study enables the development of more targeted and effective preventative and management strategies in these regions.