Chapter 19: Phylum Basidiomycota: Order Aphyllophorales—Polypores, Chantharelles, Tooth Fungi, Coral Fungi, and Corticioids

Rust fungi, classified within the order Uredinales and subphylum Pucciniomycotina, represent one of the most intricate and economically consequential groups of plant pathogens within the Basidiomycota. These obligate parasites demonstrate exceptional specialization through extraordinarily complex life cycles that frequently encompass five distinct spore morphologies, including spermatia, aeciospores, urediniospores, teliospores, and basidiospores, each serving specific ecological and reproductive functions. Many rust species are heteroecious, meaning they require two unrelated host plants to complete their developmental cycle, a feature that dramatically influences their epidemiology and control strategies. The chapter examines representative species such as Puccinia graminis, responsible for wheat stem rust disease, and Cronartium ribicola, the causative agent of white pine blister rust, illustrating how rust fungi have shaped agricultural history and prompted significant advances in plant pathology research. Structural specializations including uredinia, telia, and aecia are explored alongside the morphological characteristics and dispersal mechanisms of individual spore types, providing insight into how these fungi establish and maintain infections across host tissues. The obligate biotrophic nature of rust fungi, wherein they depend entirely on living plant cells for survival and reproduction, reflects intricate coevolutionary relationships between pathogen and host. The chapter emphasizes the substantial agricultural and ecological impacts of rust diseases, ranging from devastating crop losses in cereal and legume production to their influence on tree health and ornamental plant cultivation. Molecular investigations have refined our understanding of rust taxonomy and host-pathogen interactions, revealing the sophisticated mechanisms underlying their parasitic success. By synthesizing life cycle complexity, pathogenic strategies, and global significance, the chapter demonstrates how rust fungi exemplify fungal specialization and remain critical concerns for food security worldwide.