2. Colorado State University Research Updates
Assessment of disinfectants for control of Phytophthora
ramorum
Steven E Newman, Ph.D., M.S.
Greenhouse Crops Extension Specialist and
Professor of Floriculture
ProGreen EXPO
17 January 2013
3. Assessment of disinfectants for control
of Phytophthora ramorum
• Collaborative project between:
– CSU Agricultural Experiment Station
– USDA-APHIS Center for Plant Health Science and
Technology
4.
5. Team
• Steven E. Newman – co-principal investigator
• Craig Ramsey – co-principal investigator
• Heather Hammack – MS horticulture student
• Debra Newman – research associate
6.
7. Goals of this project
• Test oxidant disinfectants for decontamination of
greenhouse supplies, contaminated soil, and infected
plants that are contaminated with a fungal surrogate
for P. ramorum.
• The main objectives of this project are to determine:
– efficacy of oxidants on greenhouse supplies and
equipment,
– decontamination of greenhouse soil, and
– phytotoxicity of oxidants to selected nursery plants.
8. Phytophthora ramorum
• Sudden oak death carried by (P. ramorum) is a
fungal pathogen that infects over 120 plant hosts
and is threatening shrub propagation in many
U.S. nurseries.
• Oomyctes in the genus Phytophthora are the
most destructive plant pathogens in agricultural
and nursery production today.
9. Phytophthora ramorum
• Spore structures from this pathogen can survive
in water and soil, which allows them to be widely
dispersed by natural causes and by national
transportation networks.
• Inorganic disinfectants based on oxidant
chemistry have a low risk of inducing microbial
resistance due to their multi-site, mode of action.
12. Oxidation Reduction
Oxidation is defined as an increase
in the positive oxidation number
with a corresponding loss of
electrons
Reduction is a decrease in
the positive number of ions
with a corresponding gain in
electrons
13. Common industrial oxidizers and their potential relative to chlorine
Oxidation potential Oxidation relative
Oxidant (mV) to chlorine
Fluorine 3,050 2.25
Ozone 2,070 1.52
Hydrogen peroxide 1,780 1.31
Potassium permanganate 1,680 1.25
Chlorine dioxide 1,570 1.15
Chlorine 1,360 1.00
Bromine 1,070 0.70
14. Water solutions of sodium hypochlorite and its impact on
oxidation reduction potential and pH
Oxidation potential
NaOCl (%) (mV) pH
Water 210 6.8
0.3 715 8.9
0.5 690 9.6
1.0 655 10.1
1.5 630 10.6
2.0 599 11.2
3.0 570 11.7
15. Pathogen survival from laboratory simulations and
hydrocooler studies according to Suslow (2003)
Survival at ORP (mV)
Pathogen < 485 550<X<620 >665
E. coli O157:H7 > 300 s < 60 s < 10 s
Salmonella spp. > 300 s > 300 s < 20 s
L. monocytogenes > 300 s > 300 s < 20 s
Thermotolerant coliform > 48 hr > 48 hr < 30 s
21. Chlorine Dioxide Gas pure
membrane
Sodium
chlorite
from storage
25x more active
+ than chlorate
Cell Water No trihalomethanes
Water
Pump Weak caustic
Control - soda
system
22. Lang, J. M., Rebits, B., Newman, S.
E., and Tisserat, N. 2008.
Monitoring mortality of Pythium
zoospores in chlorinated water
using oxidation reduction
potential. Online. Plant Health
Progress doi:10.1094/PHP-
2008-0922-01-RS.
23.
24.
25. Contact Information
• Review and share this presentation:
http://www.slideshare.net/snewman7118
• Website:
http://www.greenhouse.colostate.edu
• eMail:
Steven.Newman@Colostate.edu
Hinweis der Redaktion
The fluorescent data was analyzed separately from the foliar data, because of four leaf samples per plant did not match with the dataset containing the single plant data for the foliar growth and morphology data. In general, the fluorescent results differed, or only slightly mirrored the results from the plant growth and leaf morphology analysis. The Fv/Fm results show that all five study factors had a significant effect on plant fluorescence. Also, there were six significant two-way interactions among the study factors, not including soil temperature. Finally, there were three significant, two-way interactions between soil temperature and the study factors. In general, Fv/Fm measurements increased as the time of measurement increased from 8 to 16 days after treatment or CFF inoculation. In other words, the plants appear to be resisting the wilt bacteria over time, or showing less biotic stress symptoms over time. Fv/Fm increased from 0.81 to 0.82 for the control and Electrobiocide + surfactant treatments when measured at 8 and 16 days, respectively. A comparison between the oxidant treatments and the control plants show that plants were less wilt stressed, i.e. had higher Fv/Fm values, for some oxidant treatments when compared to the control. The complexity describing each of the six two-way interactions in a simple summary is difficult at best, and may be misleading at worse. A full description of all the interactions will be described in journal article written for this study. Â The results for the leaf area, foliar biomass, and relative growth rate analysis for the fourth study reveal a somewhat different set of interactions between the three study variables. In general, there was one significant two way interaction (inoculation date * inoculation status) for the analysis for total leaf area, fresh and oven dry above ground biomass, SLA, and relative growth rate. Each of the study factors (chemical treatment, inoculation date, and inoculation status) had a slightly different plant growth response, but the overall study factor effects tended to mirror each other. The Relative Growth Rate (RGR) response reveals that the inoculation date or whether the plants were inoculated with CFF before or after the chemical treatments had a significant effect on the plant growth. Plants that were treated with the oxidants four days before being inoculated exhibited better overall growth. In addition, plants that were inoculated with CFF wilt had decreased growth when compared to non-inoculated plants. Finally, four out of the five chemical treatments had no effect on RGR, but chlorine dioxide + sarc did reduce RGR when compared to the four other treatments. Overall, the results show that oxidant disinfectants sprayed before the plants were inoculated resulted in better plant growth. Also, the inoculated plants did have slower growth than the non-inoculated plants. Finally, the oxidant disinfectants show some promise for improving natural plant defenses against foliar injury from the bacterial wilt. This study only had six replications among the treatments, which was not enough to lower the variation between treatments. Future studies should focus on the most effective treatments and increase the number of plant replications in order to reduce variation between treatments