Labyrinthula species associated with turfgrasses in Arizona and New Mexico

Labyrinthula terrestris, the causal agent of rapid blight disease in cool-season turfgrasses, is the first Labyrinthula species found to be associated with higher plants in terrestrial ecosystems. An initial study suggested a single common genotype associated with turfgrass in the US, but a later study revealed genetic diversity in this pathogen. In the present study, genetic diversity as well as differences in pathogenicity and morphology was determined in Labyrinthula spp. from turfgrasses in New Mexico and Arizona where rapid blight had not previously been identified. In total, 96 Labyrinthula isolates from New Mexico and four from Arizona were sequenced in 2011 and 2012. A phylogenetic approach based on 18S and ITS-LSU of ribosomal DNA was used for genotypic diversity, and pathogenicity and microscopy were used for phenotypic diversity. A maximum parsimony analysis revealed four genetic groups including two previously described Labyrinthula groups, Laby10 (L. terrestris) and Laby31. Laby10 was the most predominant with 70 % of isolates followed by Laby31 with 24 %. Two new groups, Laby879 and Laby2020, contained only five and one isolate, respectively. An association between genotypes and phenotypes was observed. Laby10 and Laby31 were highly virulent as well as larger in cell size (14.9 and 18.1 μm, respectively), while Laby879 was less virulent with an average cell size of 8.5 μm. Laby2020 was the smallest (0.8 μm) and non-pathogenic. Results showed a prevalence of pathogenic and non-pathogenic Labyrinthula spp. in turfgrasses in New Mexico and the presence of the Laby31 group in the US for the first time.