The effects of plant domestication and cultivation on nematode communities and belowground tritrophic interactions in the highbush blueberry (Vaccinium corymbosum) agroecosystem

To address how plant domestication has impacted nematode populations and interactions, the highbush blueberry (Vaccinium corymbosum) agroecosystem within the Pinelands National Reserve was selected because of the availability of nearby wild-growing stands of V. corymbosum. Over 3 years, the rhizospheric soil of both wild and cultivated plants was sampled three times per year. Alongside sampling for entomopathogenic and plant parasitic nematodes, soil abiotic traits were measured. There was an overall trend for EPN abundance to be higher in cultivated soil than wild soil. The wild sites also showed seasonal variation in EPN abundance in 2011 but not in 2012 or 2013 while the cultivated environment had more consistent abundance. EPN diversity was higher in the wild environment, and isolates from the wild showed varying virulence to Anomala orientalis larvae. Conversely, plant parasitic nematodes were more diverse in the cultivated setting. The most prevalent isolate from cultivated plants was identified as Steinernema glaseri (B1) and used in subsequent laboratory studies. The attraction of two local EPN isolates, one from cultivated plants (B1) and one from wild plants (N9), to A. orientalis larvae and wild and cultivated V. corymbosum plant roots was assessed using two-choice olfactometers. B1 was more attracted to the cultivated plants than the wild and insect feeding enhanced this attraction. N9 was more attracted to wild plants alone than wild plants with feeding larvae. From preliminary GC-MS analysis, it appears that the plant alone constitutively produces more volatiles without third instar A. orientalis feeding than with it. To test if the B1 isolate attraction and infectivity could be increased by use of known chemicals [E)-β-caryophyllene and pregeijerene], we compared the two chemicals in the laboratory and field. In six-arm belowground olfactometers, B1 was significantly more attracted to (E)-β-caryophyllene. But in the field, the differences between the treatments were not significant. However, in counting the number of EPNs successfully establishing the host in the field, the blank treatment (without attractant) attracted 2× more EPNs. In conclusion, plant domestication in a perennial setting gives rise to selection pressures on the local EPN populations to the benefit of the attraction of EPNs.Ph.D.Includes bibliographical referencesby Monique Joy River