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Take-all of wheat (Triticum aestivum L.), caused by Gaeumannomyces tritici (syn. G. graminis var. tritici), is perhaps the most important soilborne disease of wheat globally and can cause substantial yield losses under several cropping scenarios in Oregon. Although resistance to take-all has not been identified in hexaploid wheat, continuous cropping of wheat for several years can reduce take-all severity through the development of suppressive soils, a process called “take-all decline” (TAD). Extensive work has shown that TAD is driven primarily by members of the Pseudomonas fluorescens complex that produce 2,4-diacetlyphloroglucinol (DAPG), an antibiotic that is associated with antagonism and induced host resistance against multiple pathogens. Field experiments were conducted to determine the influence of agronomically relevant first-year wheat cultivars on take-all levels and ability to accumulate DAPG-producing pseudomonads within their rhizospheres in second-year field trials and in greenhouse trials. One first-year wheat cultivar consistently resulted in less take-all in second-year wheat and accumulated significantly more DAPG-producing pseudomonads than other cultivars, suggesting a potential mechanism for take-all reduction associated with that cultivar. An intermediate level of take-all suppression in other cultivars was not clearly associated with population size of DAPG-producing pseudomonads, however. The first-year cultivar effect on take-all dominated in subsequent plantings, and its impact was not specific to the first-year cultivar. Our results confirm that wheat cultivars may be used to suppress take-all when deployed appropriately over cropping seasons, an approach that is cost-effective, sustainable, and currently being used by some wheat growers in Oregon to reduce take-all. 

Abstract Introducing and characterizing variation through mutagenesis plus functional genomics can accelerate resistance breeding as well as our understanding of crop plant immunity. To reveal new germplasm resources for fungal disease resistance breeding in elite durum wheat, we challenged the diverse alleles in a sequenced and cataloged ethyl methanesulfonate mutagenized population of elite tetraploid wheatTriticum turgidumsubsp.durumcv ‘Kronos’ with stripe rust. We screened 2,000 mutant lines and identified sixteen enhanced disease resistance (EDR) lines with persistent resistance to stripe rust over four years of field testing. To find broad-spectrum resistance, we challenged these lines with other major biotrophic and necrotrophic pathogens, including those causing Septoria tritici blotch, tan spot, Fusarium head blight and leaf rust. Enhanced resistance to multiple fungi was found in 13 of 16 EDR lines. Five EDR lines showed spontaneous lesion formation in the absence of pathogens, providing new mutant resources to study plant stress response in the absence of the confounding effects of pathogen infection. We mapped exome capture sequencing data of the EDR lines to a recently released long-read Kronos genome to aid in the identification of causal mutations. We located an EDR resistance locus to an 175 Mb interval on chromosome 1B. Importantly, these phenotypically characterized EDR lines are newly described durum germplasm coupled with improved functional genomics resources that are readily available for both wheat fungal resistance breeding and basic plant immunity research.