Dissertation
STUDIES ON THE EFFECT OF HOP STUNT VIROID ON DIFFERENT HOP (Humulus lupulus) CULTIVARS
Doctor of Philosophy (PhD), Washington State University
01/2016
Handle:
https://hdl.handle.net/2376/111150
Abstract
The United States (U.S.) is the second largest producer of hops worldwide. Washington State (WA) alone accounts for 75% of U.S. hop production. A major threat to hop production globally is Hop stunt viroid (HSVd), yet very little is known about its pathogenesis. A survey of 1,635 samples from WA revealed that 17% of hop plants sampled are infected with HSVd.
To quantify the effect of HSVd infection on different cultivars, cone yield, alpha acid and beta acid content from six cultivars was measured for five consecutive years. Results revealed diverse effects of HSVd on different cultivars. In the final year, growth parameters of ‘Willamette’ and ‘Nugget’ were also measured. Internodal length, shoot length and side-arm length were significantly reduced in only HSVd-infected ‘Willamette’. Relative matter partitioning showed a similar trend in both symptomatic ‘Willamette’ and asymptomatic ‘Nugget’.
To measure the effect of HSVd on susceptibility to another major pathogen of hop, a detached leaf assay was conducted by inoculating HSVd-free and HSVd-positive leaves with hop powdery mildew (HPM). In ‘Willamette’, growth of HPM was consistently greater on HSVd-free leaves compared to leaves tested positive for HSVd. Pathogenesis-related (PR) proteins are well known for their role in plant defense responses as signaling molecules or enzymes that are usually induced upon pathogen attack. RNA sequence analysis followed by quantitative real time PCR (qRT-PCR) analysis showed that candidate PR gene transcript levels (PR1, HCH1 and TLP) increased several folds in response to HPM, and were directly proportional to HPM levels. However, levels of these three genes were unaltered by HSVd single infection, and were significantly lower in samples with mixed infection of HSVd-HPM compared to non-inoculated controls.
Reverse transcription-recombinase polymerase amplification (RT-RPA) assay was developed for HSVd diagnosis to facilitate the analysis of large sample numbers within a short period of time with less technical demands. RT-RPA assay was validated with all major variants of HSVd. RT-RPA assay results were in 100 % correlation with reverse transcription-polymerase chain reaction (RT-PCR).
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Details
- Title
- STUDIES ON THE EFFECT OF HOP STUNT VIROID ON DIFFERENT HOP (Humulus lupulus) CULTIVARS
- Creators
- Madhu Priya Darsini Kappagantu
- Contributors
- Hanu R Pappu (Advisor)Kenneth C Eastwell (Committee Member)George J Vandemark (Committee Member)Joan R Davenport (Committee Member)Stephen T.Y. Kenny (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Plant Pathology
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 198
- Identifiers
- 99900581632001842
- Language
- English
- Resource Type
- Dissertation