Role of Alternate Hosts in Epidemiology and Pathogen Variation of Cereal Rusts

Abstract

Cereal rusts, caused by obligate and biotrophic fungi in the genus Puccinia, are important diseases that threaten world food security. With the recent discovery of alternate hosts for the stripe rust fungus (Puccinia striiformis), all cereal rust fungi are now known to be heteroecious, requiring two distinct plant species serving as primary or alternate hosts to complete their sexual life cycle. The roles of the alternate hosts in disease epidemiology and pathogen variation vary greatly from species to species and from region to region because of different climatic and cropping conditions. We focus this review on rust fungi of small grains, mainly stripe rust, stem rust, leaf rust, and crown rust of wheat, barley, oat, rye, and triticale, with emphases on the contributions of alternate hosts to the development and management of rust diseases.

Saturation Mapping of a Major Effect QTL for Stripe Rust Resistance on Wheat Chromosome 2B in Cultivar Napo 63 Using SNP Genotyping Arrays

“…tritici ( Pst ) is a constant threat and as one of the most destructive diseases, it is capable of causing 5–25% yield losses, or sometimes more, in almost all wheat-growing regions (Chen, 2005; Wellings, 2011). Major stripe rust epidemics have occurred in China, with losses in some instances amounting to several million metric tons (Li and Zeng, 2002; Wan et al, 2007; Chen et al, 2009; Kang et al, 2010; Zhao et al, 2016). The most sustainable control strategy is resistant commercial cultivars (McIntosh et al, 1995; Li and Zeng, 2002; Wiesnerhanks and Nelson, 2016).…”

The transcription factor PstSTE12 is required for virulence of Puccinia striiformis f. sp. tritici

“…In addition, the expression of PstSTE12 was induced four‐fold compared with the control during the pycniospore stage in the aecial host barberry [11 days post‐inoculation (dpi)] (Fig. ), which is an alternative host for Pst (Jin et al ., ; Zhao et al ., ). The results suggest that, in addition to a role in sexual reproduction, PstSTE12 also participates in virulence.…”

Plants make galls to accommodate foreigners: some are friends, most are foes

“…If the part of the life cycle associated with a particular host is optional rather than obligatory, this alternate host is not used as frequently as the primary host. The stem rust fungus Puccinia graminis (also known as black rust) uses wheat Triticum aestivum L. as its primary host and barberry species (Berberidaceae) as its alternate host (Zhao et al , ). Barberry is where genetic recombination occurs through sexual reproduction (Berlin et al , ) and also is the only host that makes a gall for the fungus (Spooner & Roberts, ).…”

“…And yet, there is a connection between what happens on barberry and what happens on wheat: the new recombined genotypes that arise on barberry are often better equipped to overcome wheat defense mediated by Resistance genes (Singh et al , ). Removal of barberry from the landscape significantly reduces stem rust threats to wheat (Zhao et al , ).…”

“…Stem rust is a global pathogen of wheat. New stem rust strains arising on the alternate host barberry are sometimes able to overcome Resistance genes deployed in wheat (Zhao et al , ). Fortunately, hundreds of Resistance genes have been discovered in wheat and its relatives, among which have been found genes effective against new stem rust strains (Singh et al , ; Dean et al , ; Harris et al , ; Lorrain et al , ).…”