Wheat Cultivar-Specific Selection of 2,4-Diacetylphloroglucinol-Producing Fluorescent Pseudomonas Species from Resident Soil Populations

Abstract

An emerging body of evidence indicates a role for plant genotype as a determinant of the species and genetic composition of the saprophytic microbial community resident to the rhizosphere. In this study, experiments were conducted to determine the capacity of five different wheat cultivars to enhance resident populations and support introduced strains of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing fluorescent pseudomonads, a group of bacteria known to provide biological control of several soilborne diseases. When soils were cropped with three successive 28-day growth cycles of wheat, the 2,4-DAPG-producing strains were consistently recovered from the rhizosphere of the cultivar Lewjain, and commonly were present at populations higher than those recovered from other wheat cultivars. Based on restriction fragment length polymorphism and sequence analyses of phlD, a key gene involved in 2,4-DAPG production, two previously undefined phlD+ genotypes, referred to as genotypes PfZ and PfY, were discovered. Wheat cultivar Lewjain was the primary source of genotype PfY while cultivar Penawawa yielded the majority of genotype PfZ. Based on 16S rDNA sequence analysis, both new phlD genotypes were classified as P. fluorescens. Comparison of the rhizosphere competence of 2,4-DAPG-producing P. fluorescens Q2-87 (genotype B) and P. fluorescens LR3-A28 (genotype PfY) showed that both strains persisted at similar populations in the rhizosphere of all cultivars tested over a 30 day period when introduced as a seed inoculant. However, when strain LR3-A28 was applied as a soil inoculant, this strain was recovered at higher populations from the rhizosphere of wheat cultivar Lewjain than from the rhizospheres of two other cultivars. No cultivar effects were shown for strain Q2-87. Collectively, these results add further to evidence indicating a degree of specificity in interactions between plant cultivars and specific members of the saprophytic microbial community. Furthermore, as 2,4-DAPG-producing fluorescent Pseudomonas spp. have a central role in the spontaneous reduction in severity of take-all disease of wheat in response to continuous wheat monoculture, we postulate that the use of specific cultivars, such as Lewjain, which possess a superior capacity to enhance resident soil populations of these bacteria may have potential to reduce the length of the monoculture period required to induce natural suppressiveness of soils toward this disease.

Effect of sorghum seedlings, and previous crop, on soil fluorescent Pseudomonas spp.

“…Sorghum can be used in rotations, as a cover crop or as a preplant treatment because of its potentially negative impacts on weeds (reviewed in Anaya 1999) and plant parasitic fungi (Singh et al 1990) and nematodes (Rupe et al 1997). Cycling may be a way to enhance these effects (Raaijmakers and Weller 2001;Mazzola and Gu 2002;Mazzola et al 2004). In the present study, an examination of phenotypes and genotypes of fluorescent Pseudomonas spp.…”

“…Wheat (Triticum aestivum L.) cultivar Lewjain was used as a positive control for induction of growth of Phl-producing fluorescent Pseudomonas spp. (Mazzola et al 2004). Lewjain seed was obtained from K. Garland-Campbell (USDA-ARS, Pullman, WA).…”

“…Amplifications were conducted using primers Phl2a and Phl2b for Phl and PCA2a and PCA3b for PCA (Raaijmakers et al 1997). Reactions were 25 μl volumes including 1.5 mM MgCl 2 and 2.0 to 2.5 U of Amplitaq Gold [Applied Biosystems (AB), Foster City, CA USA] (Raaijmakers et al 1997;Mazzola et al 2004). Amplifications were conducted on Gene Amp® PCR System 9700 (AB).…”

Genotype-Specific Enrichment of 1-Aminocyclopropane-1-Carboxylic Acid Deaminase-Positive Bacteria in Winter Wheat Rhizospheres

“…Alternatively, RonL may be more effective at recruiting and selecting certain ACC+ bacteria than the other genotypes, presumably through production of root chemical signals. Soil microbial communities are known to vary under the influence of different genotypes of the same plant species, including wheat (Chanway et al, 1988;Mazzola et al, 2004;Micallef et al, 2009;Manter et al, 2010;Peiffer et al, 2013;Donn et al, 2015). Such biological interactions in the rhizosphere are primarily mediated by root exudates, which can serve as signals to promote chemotaxis (Gaworzewska and Carlile, 1982;de Weert et al, 2002), initiate symbiotic interactions (Oldroyd and Downie, 2008), act as substrates promoting growth of specific microbes, or any combination of these.…”

Caracterização morfocultural, biossíntese de autoindutor e formação de biofilme por rizobactérias de hortaliças

“…Possivelmente, a maior riqueza e a diversidade das estirpes encontradas na rizosfera de couve refletem a pressão exercida pelos genótipos vegetais sobre a comunidade microbiana associada, por meio da quantidade e da qualidade dos exudatos radiculares que atuam de forma seletiva sobre as populações de bactérias fluorescentes (Mazzola et al, 2004). É importante ressaltar que o manejo do agroecossistema do qual foram coletadas as espécies olerícolas, e o estádio de desenvolvimento do vegetal, época do ano, assim como o esforço na obtenção das amostras e metodologia de isolamento são variáveis que podem contribuir com os resultados obtidos.…”