A population genetics study of Lecanosticta pharomachri, a growing threat to Colombian pine plantations.

Piso, A.*, Wingfield, M. J., Rodas, C. A., Barnes, I.

Forestry and Agricultural Biotechnology Institute (FABI), Department of
Biochemistry, Genetics and Microbiology, University of Pretoria, Pretoria 0002,
South Africa

Pine needle blight diseases are some of the most damaging foliage diseases affecting forestry plantations globally. Recent outbreaks of needle blight disease symptoms in Colombian pine stands have raised concerns, as these symptoms were on Pinus species, including P. patula and P. maximinoi, previously thought to be tolerant to needle blight diseases. Two pathogens were identified causing the symptoms, namely Dothistroma septosporum and Lecanosticta pharomachri. Lecanosticta pharomachri was first described from Central America and has only recently been discovered in Colombia. Nothing is known regarding the genetic diversity or the population structure of this pathogen. The aim of this study was to develop a robust set of polymorphic microsatellite markers for L. pharomachri to be used in population genetics studies on isolates obtained from Guatemala and Colombia, the native and introduced ranges of these pathogens, respectively. Genomes of L. pharomachri, one from each country, were sequenced using Illumina sequencing. These were used to design twenty primer pairs targeting di-, tri-, tetra-, penta- and hexa-nucleotide repeat regions. From these, a set of 12 polymorphic microsatellite markers was optimized and screened on a population of 115 L. pharomachri isolates from four host Pinus species, collected from 13 farms in Colombia and two from Central America. Preliminary data revealed 104 unique genotypes with isolates from Central America forming a separate cluster from the Colombian population. These markers will now serve as a resource for other population genetics studies on L. pharomachri, especially in countries where it is emerging as a significant threat.

Keywords: population genetics study, Lecanosticta pharomachri, Dothistroma needle blight, brown spot needle blight