RUST FUNGI AND HOST PLANT COEVOLUTION: DO PRIMITIVE HOSTS HARBOR PRIMITIVE PARASITES?

Area of Science:

• * Fungal Phylogenetics
• * Plant Pathology
• * Evolutionary Biology

Background:

• * Classical view posits primitive rust fungi on ferns and conifers.
• * This was based on the assumption of host-parasite coevolution (co-speciation).
• * Assumed primitive hosts harbor primitive parasites.

Purpose of the Study:

• * To reconstruct the evolutionary history of rust fungi (Pucciniales).
• * To test the hypothesis of long-term co-speciation between rusts and their hosts.
• * To investigate evolutionary trends in rust spore stages and life cycles.

Main Methods:

• * Cladistic analysis of 30 rust genera using 28 representative characters.
• * Analysis focused on major patterns of rust fungi diversity.
• * Independent cladistic analyses of both hosts and parasites were stressed.

Main Results:

• * Tropical short-cycle rusts on angiosperms represent the basal group.
• * Rusts on conifers and ferns (Melampsoraceae) form a nested, derived clade.
• * Host transfer events appear as frequent as co-speciation.

Conclusions:

• * Rust fungi and their hosts have not undergone extensive parallel cladogenesis.
• * Heteroecism (requiring multiple hosts) is a derived trait that evolved multiple times.
• * Urediniospores likely preceded aeciospores and pycniospores in Uredinales evolution.