Thesis
Utility of Brassica juncea seed meal soil amendment and Pseudomonas fluorescens SS101 for long-term suppression of apple root infection by Pythium spp.
Washington State University
Master of Science (MS), Washington State University
2011
Handle:
https://hdl.handle.net/2376/102203
Abstract
Apple replant disease is a serious obstacle to reestablishment of viable orchards on sites previously cultivated to apple or closely related species. Pythium spp. contribute to development of apple replant disease. Brassica juncea seed meal soil amendment can effectively suppress Pythium via generation of biologically active allyl isothiocyanate (AITC). Preliminary evidence indicates that long-term control of this pathogen may be attained despite the fact that more than 99% of AITC emission occurs within 24 h of seed meal amendment. Greenhouse trials were conducted to assess the capacity of B. juncea seed meal to suppress apple seedling root infection caused by Pythium abappressorium in AITC evacuated soils. Incorporation of seed meal into orchard soil consistently suppressed apple seedling root infection by P. abappressorium even after AITC release from soil. Incubation of soil under enclosed conditions for 48 h immediately after seed meal addition significantly reduced root infection. Seed meal particle size did not influence the degree of disease suppression in AITC evacuated soil. Pasteurization of seed meal-amended soil to diminish activity of the resident soil biology eliminated disease suppression in AITC evacuated soil. Distinct changes in fungal communities induced by seed meal amendment were associated with disease suppression. AITC evacuated soil also demonstrated the potential to suppress the stimulatory effect of B. napus seed meal application on root infection by P. abappressorium. Evacuation of AITC from orchard soils prior to infestation with P. abappressorium and observed changes in fungal community composition suggest that disease suppression does not operate completely via chemical means. Thus, changes in the structure of fungal communities in B. juncea seed meal amended orchard soils may affect the long-term disease suppression response. P. fluorescens SS101 was reported to be antagonistic to Pythium spp. due to its ability to produce the cyclic lipopeptide surfactant massetolide A. Strain SS101 initially became established and persisted in the rhizosphere of apple rootstocks of the Geneva and Malling series at high density but populations declined over time. Soil amendment of this bacterial strain effectively suppressed root infection caused by P. abappressorium for the rootstocks G16, M9 and MM106.
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Details
- Title
- Utility of Brassica juncea seed meal soil amendment and Pseudomonas fluorescens SS101 for long-term suppression of apple root infection by Pythium spp.
- Creators
- Dona Muditha Nilanthi Weerakoon
- Contributors
- Mark Mazzola (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Plant Pathology, Department of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525073401842
- Language
- English
- Resource Type
- Thesis