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theses

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.

ETD_10304

Ph.D.

Includes bibliographical references

doi:10.7282/t3-sbsy-wc24

ETD doctoral

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