Suppression of Specific Apple Root Pathogens by Brassica napus Seed Meal Amendment Regardless of Glucosinolate Content

Abstract

The impact of Brassica napus seed meal on the microbial complex that incites apple replant disease was evaluated in greenhouse trials. Regardless of glucosinolate content, seed meal amendment at a rate of 0.1% (vol/vol) significantly enhanced growth of apple and suppressed apple root infection by Rhizoctonia spp. and Pratylenchus penetrans. High glucosinolate B. napus cv. Dwarf Essex seed meal amendments did not consistently suppress soil populations of Pythium spp. or apple root infection by this pathogen. Application of a low glucosinolate containing B. napus seed meal at a rate of 1.0% (vol/vol) resulted in a significant increase in recovery of Pythium spp. from apple roots, and a corresponding reduction in apple seedling root biomass. When applied at lower rates, B. napus seed meal amendments enhanced populations of fluorescent Pseudomonas spp., but these bacteria were not recovered from soils amended with seed meal at a rate of 2% (vol/vol). Seed meal amendments resulted in increased soil populations of total bacteria and actinomycetes. B. napus cv. Dwarf Essex seed meal amendments were phytotoxic to apple when applied at a rate of 2% (vol/vol), and phytotoxicity was not diminished when planting was delayed for as long as 12 weeks after application. These findings suggest that B. napus seed meal amendments can be a useful tool in the management of apple replant disease and, in the case of Rhizoctonia spp., that disease control operates through mechanisms other than production of glucosinolate hydrolysis products.

The rhizosphere: a playground and battlefield for soilborne pathogens and beneficial microorganisms

“…and the nematode Pratylenchus penetrans, but did not consistently suppress soil populations of Pythium spp. and control apple root infection (Mazzola et al 2001). Mazzola (2007) suggested that the role of the isothiocyanates could be mediated by select groups of indigenous populations of microorganisms whose presence and sufficient population density are necessary to achieve disease control.…”

Cyclic Lipopeptide Surfactant Production by Pseudomonas fluorescens SS101 Is Not Required for Suppression of Complex Pythium spp. Populations

“…Brassicaceae seed meal amendments have demonstrated the capacity to suppress various components of the pathogen complex that incites apple replant disease, including Rhizoctonia solani and Pratylenchus penetrans (21,22). In contrast, the diverse populations of Pythium spp.…”

“…In contrast, the diverse populations of Pythium spp. that contribute to this disease phenomenon is stimulated by soil amendment with seed meals of Sinapis alba or low glucosinolate-containing cultivars of Brassica napus (4,20,21), thus placing limits on the utility of this approach for disease control. An integrated system which employs a post-plant application of mefenoxam in concert with pre-plant seed meal amendment is a viable control practice in conventional orchard production (22), but is not compatible with organic production systems.…”

Revitalizing the winter turnip rape crop in the northern latitudes

“…Glucosinolates and their degradation products do not, however, solely explain the allelochemical effects of Brassica species in crop rotations and some caution should be paid in application of brassica seed meal, since at high concentrations (2% vol/vol) it can be phytotoxic, for example to apple (Malus )domestica Borkh.) (Mazzola et al, 2001).…”