Hazelnuts rank 6th in world tree nut production, with approximately 800,000 metric tons produced per year. Commercial hazelnut production in the United States (the third largest producer of hazelnuts in the world) has been limited, due to the fungal pathogen Anisogramma anomala, the causal agent of eastern filbert blight (EFB). Interestingly, A. anomala is most deadly to the European hazelnut species (Corylus avellana), the only species used for commercial production, but is harbored by and does not cause symptoms in the native American species (C. americana). This fungal pathogen invades the vascular system of hazelnuts, girdles branches, and ultimately leads to death of the tree. Control measures to combat EFB are expensive and labor intensive, thus the most cost effective means of combating this disease is the use of disease resistant plant material. The Corylus genus holds 10 additional species, many of which carry EFB resistance. Over the past 15 years, extensive germplasm collection trips have been made to develop a broad hazelnut germplasm collection at Rutgers University, the entirely of which has been screened for resistance to EFB. The purpose of this study was to genetically characterize the novel collection of largely EFB resistant germplasm at Rutgers University using simple sequence repeat (SSR) markers. In addition, these same tools were used to further enhance the utility and better direct the use of this germplasm in the breeding program by performing a population structure analysis of A. anomala isolates collected from the United States and Canada. The final aspect of this dissertation investigates additional Corylus species by conducting a lipid content and profile analysis of four hazelnut species and interspecific hybrids to determine if there is a species effect on important kernel characteristics. Both the hazelnut germplasm collection and A. anomala isolate collection were found to be highly genetically diverse, and the analysis resolved 11 and 22 genetic populations, respectively. It was also found that the lipid content and profiles of hazelnuts will likely not be negatively affected by the introgression of different species into the breeding program. This work has demonstrated that there are a number of diverse sources of resistance in the Rutgers University hazelnut germplasm collection to the exceedingly genetically diverse fungus A. anomala, and introgression of sources of resistance in non C. avellana species will likely not effect commercially important kernel characteristics.

Advisors/Committee Members: Molnar, Thomas J (chair), Simon, James E (internal member), Honig, Joshua A (internal member), Hillman, Bradley I (internal member), Wadl, Phillip (outside member).

Colletotrichum fioriniae is an important hemibiotrophic pathogen limiting both highbush blueberry (Vaccinium corymbosum L.) and cranberry (V. macrocarpon Aiton) production worldwide. Since fungicide applications during bloom are most effective in both crops, the link between host floral signals and pathogen disease cycles were investigated. C. fioriniae as well as two other latent infection forming cranberry fruit rot pathogens C. fructivorum (C. gloeosporioides s.l.) and Coleophoma cylindrospora (C. empetri s.l.) and a mature fruit infecting fungi Allantophomopsis lycopodena were investigated to better describe the temporal dynamics of pathogen stimulation in response to host derived signals produced during bloom. In order quantify this relationship and visualize pathogen responses, host signals isolated via water or chloroform were utilized in extract-dependent bioassays. The results showed that blueberry and cranberry (as well as multiple other ericaceous species) floral extracts (FEs) affected two important disease cycle stages by stimulating an increased rate (+ 200%) and quantity (+ 500%) of secondary conidiation (inoculum build-up) and appressorial formation (infection structures) of C. fioriniae and all other pathogens evaluated, except A. lycopodena, linking bloom period infecting fungi to floral signals. Conidia in the presence of FEs also conferred higher levels of disease on detached fruit than conidia alone, suggesting that apparent disease was a function of increased appressorial formation. Bioactivity was readily detected in floral rainwater runoff and became more stimulatory as proximity to flowers or the bloom period increased, thus indicating both mobility of floral signals and the importance of phenology-specific cues. Chloroform-based extractions provided a chemical mirror of the host cuticles first encountered by pathogens. Characterization of multiple tissue types elucidated fatty acid derivative compositional patterns, where specific stimulatory compounds were more abundant in flower cuticular waxes. Multiple fatty acids were identified that stimulated appressorial formation, however, hexadecanoic fatty acid derivatives were concluded to be the most likely source of stimulation due to the paired bioactivity observations and occurrence of this compound within both water- and chloroform-based extraction types. This research provides strong evidence that flowers contribute substantially to the disease cycle events of replication (sporulation and secondary conidiation) and infection of fruit by C. fioriniae and other bloom period infecting fungi, thus providing evidence as to why the bloom period is often referred to as the critical disease control window.

Advisors/Committee Members: Oudemans, Peter V. (chair), Hillman, Bradley I. (internal member), Kobayashi, Donald Y. (internal member), Polashock, James J. (outside member), School of Graduate Studies.

The transmission of insect-borne pathogens mainly relies on the foraging and feeding behavior of their insect vectors. Changes in phytochemicals, especially volatiles, nutrients and chemical defenses, of host plants from pathogen infection can facilitate the performance and preference of insect vectors. Moreover, in the ecosystem, these changes in infected host plants can also affect non-vector herbivorous insects. In the American cranberry, Vaccinium macrocarpon Ait., false blossom disease is caused by a phytoplasma that requires the blunt-nosed leafhopper, Limotettix vaccinii Van Duzee, as a vector. In this study, we hypothesized that (1) phytoplasma infection enhances L. vaccinii performance and preference on infected plants, (2) phytoplasma infection enhances the performance of three non-vector leaf feeders, and (3) phytoplasma infection alters levels of phytochemicals and expression of gene related to primary (i.e., nutrients) and secondary (i.e., plant defenses) metabolism in cranberries. Phytoplasma infection had conflicting effects on its vector. L. vaccinii had similar survival rates on infected and uninfected cranberries; however, nymphs developed more slowly and adults had higher mass on infected plants than on uninfected plants, indicative of a short-term positive effect. In contrast, female L. vaccinii laid less eggs on infected plants than uninfected plants, indicative of a potential negative long-term effect on population size. In no-choice tests, L. vaccinii preferred volatiles from uninfected plants; uninfected plants emit higher volatile emissions than infected plants. Besides these effects on the vector, larvae of three common non-vector herbivores: spotted fireworm (Choristoneura parallela Robinson), Sparganothis fruitworm (Sparganothis sulfureana Clemens), and gypsy moth (Lymantria dispar L.) had 2-3 times higher mass, and damaged 1.5-3.5 times more leaves, when feeding on infected vs. uninfected plants. Larval survival of S. sulfurena and L. dispar also improved on infected plants. Nutrient levels were higher in infected plants, while defensive proanthocyanidins were lower, which may explain the short-term benefits in performance by vector and non-vector herbivores. Phytoplasma infection induced expression of 132 genes and suppressed expression of 225 genes in cranberries. Expression of genes associated with nutrient metabolism (i.e., carbohydrate) were up-regulated, while those associated with defensive pathways were down-regulated, in the phytoplasma-infected plants. Our study suggests that phytoplasma-infected plants may rely on visual cues and volatiles from neighboring uninfected plants to attract its vector L. vaccinii. After attraction, L. vaccinii feeding might be facilitated through elevated nutrient and reduced defensive metabolite levels in infected plants. These findings support the "vector manipulation hypothesis." This vector facilitation also benefits other, non-vector, herbivores in the cranberry community. A better understanding of the mechanisms underlying tri-partite… Advisors/Committee Members: Rodriguez-Saona, Cesar (chair), Hamilton, George C. (internal member), Morin, Peter J. (internal member), Hillman, Bradley I. (internal member), Mescher, Mark C. (outside member), School of Graduate Studies.