Somatic Hybridization in the Uredinales

Abstract

Rust fungi are cosmopolitan in distribution and parasitize a wide range of plants, including economically important crop species such as wheat. Detailed regional, national, and continental surveys of pathogenic variability in wheat-attacking rust pathogens over periods of up to 90 years have shown that in the absence of sexual recombination, genetic diversity is generated by periodic introduction of exotic isolates, single-step mutation, and somatic hybridization. Laboratory studies have provided evidence for somatic hybridization between many rust species and formae speciales, and there is evidence for the process in nature within and between rust species on Linum, poplar, Senecio, wheat, and several grass species. Although the mechanisms involved in somatic hybridization are not well understood, they are thought to involve the fusion of dikaryotic vegetative hyphae, nuclear exchange, and possibly exchange of whole chromosomes between nuclei or parasexuality via the fusion of the two haploid nuclei, followed by mitotic crossing over and vegetative haploidization. In three cases, hybrid isolates rendered resistant plant genotypes susceptible because of new combinations of virulence. Implications for resistance breeding and future prospects in understanding the process are discussed.

Phylogenetic Analysis Reveals a High Prevalence of Sporothrix brasiliensis in Feline Sporotrichosis Outbreaks

“…In many plant-pathogenic fungi, such as Fusarium and Alternaria , pathogenicity is determined by mobile, dispensable small chromosomes [80], [81]. Genetic processes such as hybridization of two distinct, sympatric species [82], parasexual recombination [83], [84] or mechanisms of inactivation/activation of virulence genes by insertion of transposons [85] can also drive the emergence of pathogenicity. Hybridization is one of the possible mechanisms of emergence of phytopathogenic fungi [86], [87] as well as fungi pathogenic to animals [88].…”

Rust fungi and global change

“…This process can be aided by rust somatic recombination and sexual hybridization, as demonstrated in hybrid cereal rusts (Park & Wellings, ) and poplar rust fungi (Spiers & Hopcroft, ). Global change is projected here to increase the rusts’ ability to generate new virulence combinations: (1) host plant homogenization leads to greater numbers of susceptible individuals, allowing higher numbers of recombinants to be produced (Park & Wellings, ); and (2) the bringing together of hitherto separate rust genotypes through global movement of pathogens provides the opportunity for novel hybrid species to be generated. While many of these new recombinations are expected to be less aggressive than their parent strains, occasional more highly adapted strains are likely to emerge and, given the availability of susceptible host plants, may cause unprecedented epidemics (Kerr & Keane, ).…”

Genome size analyses of Pucciniales reveal the largest fungal genomes

“…Rust fungi are able to infect plants from most families, including conifers, ferns and mosses, and are responsible for major diseases on agricultural and forest crops worldwide. Rust epidemics have impacted the development of human society, such as the early accounts of cereal rusts coming from the Bible and from Greek and Roman literatures (Park and Wellings, 2012), or the reports of coffee leaf rust epidemics in Sri Lanka in the 19th century (Silva et al, 2006). …”