Associations Among Cultivar Cropping Sequence, 2,4-Diacetlyphloroglucinol–Producing Pseudomonad Populations, and Take-All Disease of Winter Wheat in Oregon

Take-all of wheat (<i>Triticum aestivum</i> L.), caused by <i>Gaeumannomyces tritici</i> (syn. <i>G. graminis</i> var. <i>tritici</i>), 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 <i>Pseudomonas fluorescens</i> 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.