Sexual reproduction in populations of Austropuccinia psidii

Abstract

Austropuccinia psidii is a rust fungus that has expanded its known geographic distribution and host range on Myrtaceae. Invasions by rust fungi are often caused by asexual urediniospores that give rise to populations with low genotypic diversity. Recently it was shown that basidiospores, the gametic spores of A. psidii, were able to infect species of Myrtaceae under controlled conditions. The present study tested the hypothesis that sexual reproduction occurs through infection of Myrtaceae by basidiospores of A. psidii in recently invasive populations from New Zealand and South Africa. We provided three lines of evidence to test this hypothesis, i) presence of a sexual stage, ii) high genotypic diversity within an invasive population and iii) no genetic linkage between microsatellite markers in multilocus genotypes.Our results provide evidence that invasions of A. psidii are caused by both urediniospores that spread clonal genotypes, and teliospores that produce recombinant basidiospores, which infect Myrtaceae. We reject the hypothesis that field infections of A. psidii are only caused by asexual urediniospores, and support that sexual reproduction occurs in invasive populations and may accelerate adaptation to environmental change.

Susceptibility of native New Zealand Myrtaceae to the South African strain of Austropuccinia psidii: A biosecurity threat

“…psidii strains. The host range of the South African strain, based on artificial inoculations and field surveys (McTaggart et al, 2020; Roux et al, 2016), now includes 21 species. The wide host range of the South African and pandemic strains are unusual compared to other host‐specific A .…”

“…Recombination occurring at the teliospore stage creates genotypic diversity that could increase the speed at which A . psidii adapts to new hosts and environments (McTaggart et al, 2020). This could be further hastened by the ability of this strain to complete its life cycle within a short period of time (3 weeks observed in this study), demonstrating its increased adaptive potential.…”

“…psidii and the influence of environment, host, and strains are yet to be determined. It is still unknown whether the South African and the pandemic strains are reproductively compatible, but based on the life cycle described by McTaggart et al (2020), different strains of A . psidii could potentially hybridize if their basidiospores infect the same host.…”

“…The origin of this strain is not known, and to date it has not been reported in any other country, including those in South America. Since its first detection in 2013, this strain has expanded its distribution to seven of the nine provinces of South Africa (McTaggart et al, 2020; Roux et al, 2016). Seventeen host species for the South African strain have been reported from surveys and artificial inoculations, including near‐threatened native species and non‐native ornamental trees (McTaggart et al, 2020; Roux et al, 2016).…”

“…Evidence for genetic recombination in the field only seven years after its first detection in South Africa represents a major biosecurity risk. This is because the rust is increasing not only its genetic diversity, but also in its adaptability (McTaggart et al, 2020). Global movement of plant material (Wingfield et al, 2015) and the ability of A .…”