Differential Susceptibility of Diverse Salix spp. to Melampsora americana and Melampsora paradoxa

Abstract

Melampsora spp. willow rust is the most serious disease of shrub willow bioenergy production in the northeastern United States. Recent phylogenetic studies have identified several Melampsora spp. present on willow in the Northeast; however, in-depth understanding of Melampsora spp. host susceptibility remain unresolved. In this study, a panel of 82 rust isolates collected from the northeastern United States were genotyped via ribosomal DNA sequencing and a subset of these isolates were assayed for host susceptibility. This work revealed that Melampsora americana is the most prevalent species in the sampled geographic region and that there is potential for rust resistance breeding using the Salix spp. taxa assayed. Additionally, leaf morphology traits of these Salix spp. hosts were quantified for correlation analysis, revealing that trichome density and stomata density are possible contributors to resistance. This work provides foundational rust pathology information, which is crucial for M. americana resistance breeding.

Comparative Transcriptomics And eQTL Mapping Of Response To Melampsora Americana In Selected Salix Purpurea F2 Progeny

“…Melampsora americana has previously been shown to be the dominant rust species infecting S. purpurea willow in the northeast United States, yet little is known about the mechanisms of pathogen virulence or host resistance (11,12). By applying transcriptomics on willow leaf rust and the S. purpurea host over a time series post-inoculation, we de ned gene networks associated with a reduction in photosynthesis and an increase in defense response, while simultaneously revealing candidate effectors for pathogenicity.…”

“…Plants were established from dormant stem cuttings in the greenhouse and grown for two months before inoculation. For the inoculated treatment, 1 mg of uredospores of M. americana rust isolate R15-033-03 was applied to each of ve mature leaves per plant of each genotype using a paintbrush as previously described (12). Plants were incubated for 12 h in mist chambers at 20°C with 100% humidity, then returned to greenhouse under 14:10 photoperiod at 24 o C:18 o C respectively.…”

“…Melampsora rusts infecting willow are lesser-known members of the order Pucciniales that includes wheat stem rust (Puccinia graminis), coffee rust (Hemileia vastatrix) and over 7,000 other species (9,10). Previous work has identi ed M. americana as the primary contributor to disease epidemics on S. purpurea in the northeastern US (11,12). De ned as a macrocyclic and heteroecious obligate biotroph, M. americana requires an alternate host to complete all ve spore stages in its life cycle and cannot be cultured outside of its living host (13,14).…”

“…Given the proli c nature of this disease, durable genetic resistance is essential to achieving sustained shrub willow biomass yield. Recent investigations have identi ed morphological characteristics that may impact rust infection, including stomatal density and trichome density (12), however, the genetic basis for M. americana rust resistance in willow is not well understood.…”

Mapping the sex determination region in the Salix F1 hybrid common parent population confirms a ZW system in six diverse species

“…Here, we introduce the Salix F 1 hybrid common parent population (Salix F 1 HCP). The parents, described in Fabio et al (2019) and Crowell et al (2020), represent a diverse selection of species from Salix subgenus Vetrix (Dickmann and Kuzovkina 2014). Six Salix species (S. viminalis, S. suchowensis, S. integra, S. koriyanagi, S. udensis, and S. alberti) were crossed to common male and female S. purpurea parents to form eight species hybrid families.…”