Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/19/2008
Publication Date: 1/1/2009
Citation: Mazzola, M., Brown, J., Zhao, X., Izzo, A., Fazio, G. 2009. Interaction of brassicaceous seed meal and apple rootstock on recovery of Pythium spp. and Pratylenchus penetrans from roots grown in replant soils. Plant Disease. 93:51-57. 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 conduct to assess whether the effectiveness of brassicaceous seed meal amendments for the control of pathogens that cause apple replant disease would be influenced by the apple rootstock employed. Significant interactions were detected between the seed meal type and apple rootstock in the level of control of two pathogen populations that contribute to apple replant disease; Pythium spp. and lesion nematode (Pratylenchus penetrans). Certain seed meals increased root infection by Pythium but seed meal from the mustard Brassica juncea effectively controlled disease incited by this pathogen. The composition of the Pythium population changed in response to all seed meal amendments, and addition of seed meal from the mustard Sinapis alba to soil resulted in a population composed of species with greater virulence toward apple. All seed meals evaluated significantly reduced lesion nematode populations recovered from apple roots, however, Brassica juncea seed meal was more effective than Sinapis alba seed meal or canola (Brassica napus) seed meal. S. alba and B. napus seed meal were only effective in reducing lesion nematode root populations when integrated with the use of a nematode tolerant rootstock. When used with a susceptible rootstock, only B. juncea seed meal was effective in suppressing lesion nematode root infection. New apple rootstocks from the Geneva breeding program demonstrated a significant level of tolerance to disease incited by Pythium spp. These findings demonstrate that optimal effectiveness of brassicaceous seed meals for control of apple replant disease will require integration of such soil amendments with the use of an apple rootstock possessing tolerance to individual pathogens, such as Pythium and Pratylenchus spp.,that cause apple replant disease.
Technical Abstract: Pythium spp. and Pratylenchus penetrans are significant components of the diverse pathogen complex that incites apple replant disease in Washington state. The structure of the Pythium population differs among orchard soils but is composed of multiple pathogenic species. Studies were conducted to determine the effect of brassicaceous seed meals and apple rootstock on the activity and composition of these pathogen populations. Apple rootstocks from the Geneva series consistently supported lower populations of P. penetrans than did rootstocks of the Malling or Malling-Merton series. Brassica juncea seed meal (SM) was superior to Brassica napus SM or Sinapis alba SM for the suppression of lesion nematode populations. Significant rootstock x seed meal interaction was detected, and nematode suppression in response to B. napus or S. alba SM was only observed when used in concert with a tolerant rootstock while B. juncea SM suppressed lesion nematode root populations irrespective of rootstock. Brassicaceous seed meals differed not only in capacity to suppress Pythium spp. numbers and apple root infection, but differentially transformed composition of the population recovered from apple roots. B. juncea SM was the sole seed meal examined to suppress Pythium numbers and root infection; however, a persisting population was always detected, which was dominated by Pythium irregulare. In general, the Geneva series rootstocks G11 and G30 were less susceptible to root infection by native populations of Pythium, whereas M26, MM106 and MM111 were highly susceptible. These findings demonstrate that utilization of brassicaceous seed meal amendments for replant disease suppression must employ an appropriate rootstock in order to achieve optimal disease control.