Infection process of Setosphaeria turcica in compatible, resistant and incompatible interactions

Northern corn leaf blight (NCLB) and sorghum leaf blight (SLB), caused by Setosphaeria turcica (syn. Exserohilum turcicum), are among the most important diseases affecting maize and sorghum globally. These diseases cause substantial losses underscoring the necessity for an in-depth study of this pathosystem. S. turcica strains exhibit host specificity, meaning that a particular strain can infect either maize or sorghum, but not both. This pathosystem provides a unique opportunity to study different interactions between plants and pathogen strains, and while progress has been made on the genetic characterization of these interactions, microscopic characterization has not been used on the incompatible interaction of this pathosystem. To assess variations in early colonization phenotypes among compatible, Ht resistant, and incompatible interactions (sorghum-strain on maize and maize-strain on sorghum), we inoculated maize lines B73, A619, A619_Ht1, and the sorghum line BTx623 with maize- and sorghum-specific strains of S. turcica. Early colonization phenotypes were quantified using epifluorescence microscopy. Confocal fluorescence microscopy was used to confirm results from epifluorescence microscopy and to obtain clear images of plant pathogen interactions. Significant differences in phenotypes were noted based on host-strain interactions. Incompatible interactions exhibited more appressoria, and conidia with multiple appressoria, than resistant and compatible interactions. Compatible interactions showed higher xylem and mesophyll penetration and colonization than incompatible and resistant interactions. Successful xylem penetration without colonization occurred in incompatible interactions, while resistant interactions demonstrated both xylem penetration and colonization without mesophyll colonization. These results suggest that incompatible interaction in S. turcica occurs by a different mechanism than the resistant interaction. The progeny strains derived from a biparental fungal population, resulting from a cross between maize and sorghum specific strains, were also inoculated to determine whether those strains resemble the phenotypes from the parental strains. Inoculating maize lines B73 and A619_Ht1, along with the sorghum line BTx623, with progeny strains virulent to only maize, virulent to only sorghum, virulent to both maize and sorghum, and avirulent to both maize and sorghum, yielded similar results as that of parental experiment. Incompatible interactions had more appressoria and conidia with multiple appressoria, while compatible interactions exhibited higher xylem penetration and colonization efficacy. These results largely confirm the observations with the parental strains and suggest that the mechanisms that cause incompatible resistant interactions in the fungus are heritable. Finally, propidium iodide staining was used to quantify the extent of plant cell death in compatible, resistant and incompatible interactions. The compatible interaction had a lower number of dead cells (maximum 3) under the appressoria at 8hpi. Incompatible and resistant interactions had higher number of death cells (N≅10) under an appressorium. Resistant interactions had fewer death cells than incompatible interaction but higher than the compatible interactions. These results also confirm that the incompatible interaction occurs by a separate mechanism than the resistant interaction and suggest that both incompatibility and resistance occur by a hypersensitive response.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Pokhrel, Rashmi

Contributors dc:contributor

• Mideros, Santiago
• Schroeder, Nathan
• Jamann, Tiffany

• Setosphaeria Turcica
• Host-pathogen Interactions
• Cell Death

Statement dc:rights

• Rashmi Pokhrel

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/124701

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F124701