Interaction of Brassicaceae seed meal soil amendment and apple rootstock genotype on microbiome structure and replant disease suppression

Authors: WANG, LIKUN - Washington State University; Mazzola, Mark

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2018
Publication Date: 4/16/2019
Citation: Wang, L., Mazzola, M. 2019. Interaction of Brassicaceae seed meal soil amendment and apple rootstock genotype on microbiome structure and replant disease suppression. Phytopathology. 109(4):607-614. https://doi.org/10.1094/PHYTO-07-18-0230-R.
DOI: https://doi.org/10.1094/PHYTO-07-18-0230-R

Interpretive Summary: Organic soil amendments often have been promoted as a means to control soilborne plant diseases. However, the effective use of individual amendments for the control of biologically complex diseases seems improbable. Studies were conducted to assess whether the effective control of apple replant disease could be controlled at significantly lower Brassicaceae seed meal(SM) amendment rates than used previously if used in conjunction with the appropriate apple rootstock. Significant interactions were detected between seed meal formulation application rate and apple rootstock genotype in terms of rhizosphere microbiome composition, plant growth and root infection by two pathogens that contribute to apple replant disease; Pythium spp. and lesion nematode (Pratylenchus penetrans). Although apple rootstock growth was improved at all Brassicaceae SM application rates regardless of genotype, only rootstocks G.41 and G.210 had instances where similar plant biomass was attained at both the lowest and highest amendment rate. Likewise, composition of the G.41 and G.210 rhizosphere microbiome was similar at the low and high seed meal amendment rate. Root infection by P. penetrans and Pythium spp. was lower in rootstock G.41 and G.210 relative to MM.106 and M.9 when cultivated in the control soil. Thus, among the treatments evaluated, use of G.41 or G.210 rootstock with SM applied at a rate 4.4 t ha-1 may be the most economically viable alternative to pre-plant soil fumigation for control of apple replant disease.

Technical Abstract: Pre-plant soil application of a Brassica juncea/Sinapis alba seed meal (SM) formulation at a rate of 6.6 t ha-1 can alter composition of the orchard soil microbiome in a manner that yields sustainable long-term suppression of soil-borne pathogens in apple production systems. However, the cost of SM amendment has hindered the adoption of this tactic to manage apple replant disease in commercial orchards. Greenhouse trials were conducted to assess the effect of reduced SM application rate in concert with apple rootstock genotype on structure of the soil microbiome and associated disease control outcomes. At all application rates, SM treatment increased tree growth and reduced disease development relative to the control in a manner equivalent or superior to that attained in response to soil pasteurization. In general, total tree biomass and leader length were similar in soils treated with SM at 4.4 or 6.6 t ha-1 irrespective of rootstock genotype. Similar increase in plant biomass between the lowest and highest SM amendment rate was only attained with G.210 rootstock. Suppression of Pythium spp. or Pratylenchus penetrans root densities was similar at all SM application rates. When cultivated in non-treated replant orchard soil, Geneva rootstocks exhibited lower levels of Pythium spp. and P. penetrans root colonization relative to Malling rootstocks. For a given rootstock, composition of the rhizosphere microbiome was similar in soils treated with SM at 4.4 and 6.6 t ha-1 at three months post planting. G.41 and G.210 rootstocks, but not M.9 or MM.106, cultivated in SM at 2.2 t ha-1 treated soil possessed a rhizosphere bacterial community structure that differed significantly from the control. Findings indicate that similar replant disease control efficacy and plant growth will be achieved at a reduced SM application rate (4.4 t ha-1) and overall tree performance may be possible at a lower rate if employed with the appropriate rootstock genotype.