Thesis
Seed Transmission of Pseudomonas Syringae PV. Aptata, and Efficacy of Bactericides for Control of the Pathogen in Beet and Swiss Chard Seed Production
Washington State University
Master of Science (MS), Washington State University
2023
DOI:
https://doi.org/10.7273/000006392
Abstract
Bacterial leaf spot (BLS), caused by Pseudomonas syringae pv. aptata (Psa), is an economically important disease in beet and Swiss chard production. Psa is a splash-dispersed, seedborne, and seed-transmitted pathogen, and BLS is favored by cool and moist conditions. The economic impact of BLS has increased with expansion of baby leaf beet and chard production because of the dense plantings (>7 million seed/ha) and overhead irrigation. Baby leaf production also has increased the demand for seed. Management practices for BLS are limited, e.g., disinfection of Psa-infected seed lots, use of drip irrigation (where feasible, but impractical for baby leaf crops), selection of planting sites, and foliar applications of copper bactericides. Disinfection of seed is costly. Copper bactericides are not systemic or curative, and have limited efficacy, including a risk of pathogen populations developing tolerance to copper. This study evaluated: i) thresholds for seedborne Psa that result in development of BLS in baby leaf beet and chard crops, ii) the duration of survival of Psa in beet and chard seed, and iii) the efficacy of foliar applications of various bactericides for control of BLS in seed crops. Four baby leaf field trials planted with seed naturally infected at a range of concentrations of Psa revealed the threshold for seedborne Psa that resulted in ≥5% severity of BLS ranged from 0 to ~6 x 104 CFU/g seed, depending on environmental conditions. Recovery of seedborne Psa in naturally infected beet (n = 3) and chard (n = 3) seed lots tested at 3-month intervals after harvest of seed crops revealed the amount of seedborne Psa (log10CFU)/g seed) declined by 0.07 to 0.19 X months of storage. Therefore, storing seed for 12 to 24 months may be a viable option to reduce Psa to negligible levels prior to selling the seed. Of ten bactericides evaluated in five chard seed crops, none reduced severity of BLS symptoms or Psa infection levels of the harvested seed, except ManKocide in only one trial with moderate BLS severity. Further research on seed treatments and bactericides is needed to facilitate effective management of Psa in beet and chard production.
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Details
- Title
- Seed Transmission of Pseudomonas Syringae PV. Aptata, and Efficacy of Bactericides for Control of the Pathogen in Beet and Swiss Chard Seed Production
- Creators
- Stephanie Ann Crane
- Contributors
- Lindsey du Toit (Advisor)David Weller (Committee Member)Lyndon Porter (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- College of Agricultural, Human, and Natural Resource Sciences
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Number of pages
- 113
- Identifiers
- 99901087840301842
- Language
- English
- Resource Type
- Thesis