Date of Graduation
Davis College of Agriculture, Natural Resources and Design
James B Kotcon
Gary K Bissonnette
Alan J Sexstone
Root-knot nematode (RKN) and dagger nematode (DN) are serious pests of agricultural crops, including peach trees of West Virginia. RKN is a sedentary endoparasite that feeds and reproduces within the roots of host plants, causing gall formation, loss of vigor, and plant death. DN is an ectoparasite that has the potential to vector devastating plant viruses. Many control options recommended for annual crops are not appropriate for orchards and the use of chemical nematicides is limited. The endospore-forming bacterium, Bacillus firmus (BF), is marketed as a bionematicide, though its mode of action and efficacy in controlling certain nematodes indigenous to West Virginia are unclear. The purpose of this study was to determine efficacy and mode of action of BF as a bionematicide against the northern RKN, Meloidogyne hapla and DN, Xiphinema americanum. Direct toxicity was determined by exposing RKN and DN to various concentrations of BF over a 72-hour period. Exposure to a 107 CFU/ml concentration of BF caused a 15 % decrease in living RKN and an 11 % decrease in living DN by 72 hours. No effect was observed with lower concentrations. In-vitro attraction assays were performed to determine if the presence of BF affects nematode migration and infection rates. Filter paper discs were treated with BF and sterile soil extract (SSE) and were placed at either end of a slide covered with Pluronic gel. Approximately 150 RKN or 30-50 DN were placed in the center of each slide and the number of nematodes that left the center and migrated to each side was counted at 1, 2, 4, and 24 hours post inoculation. A similar attraction assay was performed with tomato seedlings instead of filter paper. Filter paper assays showed that 93 % of motile RKN were observed on the SSE portion of the slides compared to 7 % on the BF side by hour 24. Attraction assays using tomato seedlings showed 71 % of motile RKN were observed on the portion of slides with SSE-treated roots, compared to 29 % on the side with BF-treated roots. DN results were contrary to RKN results. Filter paper assays showed 59 % of motile DN on the BF portion of slides compared to 41 % on the SSE side, while tomato seedling assays showed no significant difference between treatments at hour 24. Infection assays using seedlings on glass slides showed an average of three RKN successfully penetrated BF-treated roots compared to 20 in SSE roots. Attraction assays in sand, comparing RKN infection of BF and SSE-treated tomato seedlings, showed no significant difference between treatments. Nematode mortality observed after exposure to BF suggests that BF produces secondary metabolites that are directly toxic to RKN and DN, though these metabolites have limited potency. Behavior of RKN in the presence of BF suggests the involvement of a chemorepellent, while the behavior of DN suggests the involvement of a chemoattractant. The results of this study indicate that the mode of action of BF is linked to the production of chemorepellent compounds, though these chemotactic factors are species specific. BF is a promising biocontrol option for the management of RKN but may not demonstrate the same measure of control against DN.
Valencia, Lisa M., "Bacillus firmus for the biological control of Meloidogyne hapla and Xiphinema americanum" (2016). Graduate Theses, Dissertations, and Problem Reports. 6860.