Microbiological Improvement of Root Health, Growth, and Yield
of Strawberry
Final Report - September 2002, (Updated May 2003)
Principal Investigator:
John M. Duniway, Professor
Department of Plant Pathology
University of California, Davis
One Shields Avenue
Davis, CA 95616-8680
Telephone: 530-752-0324
Email: [email protected]
Fax: 530-752-5674
Cooperators:
Luis Guerrero and Christopher Winterbottom
California Strawberry Commission
P.O. Box 269
Watsonville, CA 95077-0269
Phone: 831-724-1301
Email: [email protected]
Fax: 831-724-0660
Kirk Larson
Department of Pomology
University of California, Davis
UC South Coast
Res. & Ed. Ctr.
7601 Irvine Blvd.
Irvine, CA 92718
Phone: 949-857-0136
Email: [email protected]
Fax: 949-653-1800
Project Locations
UC Davis Campus, Yolo Co., Monterey Bay Academy, Watsonville, Santa Cruz Co., and UC South
Coast Research and Education Center, Irvine, Orange Co.
Commodity:
Strawberry
Funding:
SAREP
Matching from the California SAREP Direct Cost
1
19992000
20002001
20012002
Direct Cost Strawberry Commission
$4,680 CSC Project to PI
$36,670
12,000 CSC Field Expenses
$4,680 CSC Project to PI
$40,260
12,000 CSC Field Expenses
$4,680 CSC Project to PI
$41,850
12,000 CSC Field Expenses
Table of Contents
Objectives
Summary
Specific Results
Potential Benefits/Impacts on Agriculture
Dissemination of Findings
Figures
Objectives
The research objective was to find and effectively deploy microorganisms to improve root health,
growth, and yield of strawberry plants without soil fumigation or with less than optimum soil fumigation
treatments. While no individual microorganism or combination of beneficial microorganisms is likely to
reproduce the large yield increases obtained by methyl bromide/ chloropicrin fumigation of soil,
evidence was found that inoculations with specific microorganisms are likely to increase yield
significantly. These increases are most likely to be useful when combined with alternatives to methyl
bromide, including fumigants other than methyl bromide. Candidate microorganisms are available
commercially, but more likely to succeed are microorganisms isolated recently from roots of strawberry
growing in fumigated soils in California. The approach was to use these microorganisms, which were
found to promote growth of strawberry plants in the greenhouse, to inoculate plants grown for berry
production in the field. Methods of field application were researched and resulting growth and yield
responses of strawberry measured relative to those obtained by normal farming practices with and
without fumigation. The educational objectives were to help demonstrate mechanisms by which
strawberry responds to soil fumigation and to scientifically explore, with grower involvement, the
feasibility of using biological agents to help improve strawberry health and yield.
Summary
We continued to sample field sites throughout the project period for additional isolates of rhizosphere
bacteria and to test their effects on the growth and health of strawberry in the greenhouse and growth
chambers. In the last 2 years, we improved our screening efficiency by testing bacteria for inhibition of
several pathogenic fungi in culture. Several new isolates with beneficial activity were found and some
were tested in the field.
2
In each of the 3 years of the grant, several bacteria (and sometimes specific fungi) were used to
inoculate strawberry plants in replicated field experiments. These were done at the Monterey Bay
Academy (MBA), Watsonville, and at the U.C. South Coast Research and Education Center (SCREC),
Irvine. Three bed fumigation treatments were applied each year at MBA, i.e., a standard rate of methyl
bromide/chloropicrin (MBC), a low rate of chloropicrin (Pic), and not fumigated. Plants were root-dip
inoculated at transplanting and some were reinoculated periodically during crop growth. While MBC
fumigation approximately doubled strawberry yields, none of the inoculation treatments increased yields
significantly in MBC-treated and very few did so in nontreated soil. In contrast, several of the bacteria
tested increased yields in soil treated with a low rate of Pic at MBA, and some of these increases were
statistically significant. Reinoculation during crop growth did not enhance the effects of the bacteria.
Additional experiments were done in the last 2 years at MBA using the variety Aromas and
nonfumigated soils. A few of the bacteria tested reduced the incidence of Verticillium wilt in 2001 and
two isolates increased yields in 2002. Aromas appears to be more responsive to bacterial inoculations
than Selva.
Sections of the ground used in 1999-2000 at SCREC were broadcast fumigated with MBC or were left
untreated. Bare-root Camarosa runner plants were obtained from a high elevation nursery and Camarosa
plug plants were propagated by Kirk Larson. In 2000-01, ground at SCREC, which was new to
strawberries, was bed fumigated with MBC, Pic, or not treated, and in 2001-02 beds were fumigated
with MBC, metam sodium, or were not treated. The field used in 2001-02 had a history of strawberry
production. Rhizosphere bacteria were used to inoculate bare-root transplants only at the time of
planting. The effects of the soil fumigation and inoculation treatments on plant size at SCREC were
variable, but fumigation generally increased yields significantly on ground with a history of
strawberries. One bacterium increased growth significantly in Pic- and non-treated soils, while two did
so following metam sodium treatment of soil. The use of plug plants in 1999-2000 had only small and
variable benefits relative to bare-root transplants.
The main aspects of these experiments are being repeated at MBA in 2002-03 with additional bacterial
isolates from strawberry and support from the California Strawberry Commission. In the 2002-03 crop
cycle, we have found that marked strains (antibiotic resistant) do colonize soil and roots following
inoculations, with high numbers on both older and new roots up to 2 months after inoculation. Dispersal
of marked strains has appeared vertically downward from the points (tested at about 10 cm). At 5
months, plants were nearly fully grown and there were still fairly high numbers of inoculated bacteria on
roots at shallow depths, but low numbers deeper in soil. There was no spread laterally at the 10 cm
distance tested. These plots are still being harvested, and net yield effects are yet to be determined.
Specific Results
Microbial Isolates - Many studies have shown that root colonization by specific bacteria or fungi can
give general increases in plant growth, yield, and/or measurable control of known root pathogens (2, 3,
11-14, 19). While most of the research has been directed at the effects of individual rhizobacteria on a
specific pathogen, individual isolates of rhizobacteria are being found to have broader spectrums of
activity against multiple plant pathogens (12, 19). In addition, rhizobacteria have recently been found to
induce systemic resistance in plants, i.e., to reduce general tissue susceptibility to various pathogens
throughout the plant (18). A number of bacteria and fungi have been inoculated to seeds or transplants to
improved plant growth, yield, or disease control in natural soils, and some of these agents have been
commercialized (2, 3, 11, 14, 19). Commercial strains of bacteria have recently been tried on strawberry
in California, but were of little benefit in a field situation where soil fumigation also gave small
increases in yield (1).
3
The PI and associates have been researching microbiological differences associated with the enhanced
growth and productivity of strawberries in soils fumigated with methyl bromide/ chloropicrin where the
response is not due to control of known, major pathogens (4-10, 16, 17). Briefly, strawberry plants in
fumigated soils consistently had much higher root length densities and fewer dark roots than plants in
nonfumigated soils. Fungi, including species of Cylindrocarpon, Pythium, and Rhizoctonia which we
find to be damaging to strawberry roots, are isolated significantly less often from roots in fumigated than
in nonfumigated soils. Populations of fluorescent pseudomonades in soil increase quickly following
fumigation to be 10-1000 fold higher than in nonfumigated soils 10 days to 9 months after fumigation.
Predominant isolates of fluorescent pseudomonades from the rhizosphere were tested for effects on
strawberry growth in natural field soil in the greenhouse. The effects of individual isolates ranged from
beneficial (increased shoot and root dry weights up to 72% and 162%, respectively) to deleterious (about
20% shoot or root reduction). Pseudomonas fluorescens, P. putida and P. chlororaphis were among the
most predominant and beneficial rhizobacteria tested. The results suggest that reductions in deleterious
fungi and increases in beneficial fluorescent pseudomonades contribute to the enhanced growth response
of strawberry to soil fumigation with methyl bromide/chloropicrin.
The main approach taken in the project reported here was to use beneficial microorganisms isolated
from strawberries in fumigated soils as inoculants in field experiments to determine the feasibility of
using microorganisms beneficial to root health and growth in strawberry production. At the start of this
project, we had a collection of candidate bacteria isolated previously from several field sites where
strawberries were grown in non-fumigated and fumigated soils with large growth and/or yield responses
to fumigation. We continued to collect new candidate isolates throughout the course of this 3-year
project. Replicate plants were dug from the soil to a depth of 20 cm and brought to the laboratory.
Young roots were carefully lifted from the soil and sub-sampled for visual assessments of root health
and transfer to buffer on a shaker. Rhizosphere soil in buffer was subsequently used for dilution plating
on three media, colonies enumerated, and random samples of each colony type transferred for pure
culture. Bacteria and fungi are also isolated from 5 mm root segments after washing in buffer.
Screening Isolates for Activity - Many individual bacteria were screened for their effects on the growth
and health of strawberry plants using a natural soil in the greenhouse or growth chamber. Individual
bacteria, kept at -80 C, were grown in TSB and used to root-dip inoculate clean, 10-week-old Selva,
Aromas, and/or Camarosa seedlings (5-7 replicates) as they were transplanted into natural field soil
(collected where strawberry is grown without fumigation) mixed with a potting soil. Two uninoculated
controls were included in each experiment, i.e., one using the natural field soil and one using heatsterilized field soil. Four to 6 weeks after inoculation, plants were washed free of soil, root health
assessed, and fresh and dry weights of roots and shoots determined. In the last 2 years of the project,
individual bacteria were also screened in culture for antibiosis to Pythium, Rhizoctonia, and
Cylindrocarpon isolates found to be damaging to strawberry roots in nonfumigated soil, and to the
known pathogens Verticillium dahliae and Phytophthora cactorum (9, 10, 17). We found that prescreening for antibiosis to one or more of the fungi greatly improved the frequency with which bacterial
isolates were found to increase the growth of strawberry seedlings (Figure 1).
Results from a representative greenhouse experiment using recent isolates having some antibiosis are
shown in Figure 2. A majority of the isolates in this experiment increased root growth measured as fresh
and/or dry weight and some also increased shoot growth. Strawberry variety did not have a significant
effect (data not shown), but soil sterilization sometimes increased uninoculated plant growth
significantly. Promising isolates were tested further using similar methods in controlled environment
chambers, and those isolates that gave repeatable growth benefits in the growth chamber were retained
for further testing and identification by fatty acid extraction and chromatography using the MIDI
system. Those bacteria having the most favorable activities were advanced to field plot testing in the
next crop cycle.
4
Inoculated Field Plots at Watsonville - Plots for the main experiments at MBA were farmed in each of 3
years by normal practices for strawberry production in the area on 2-row beds. They were located on soil
with a past history of strawberry production where general growth and yield responses to soil fumigation
were large (5-9). Three fumigation treatments were applied using a black polyethylene mulch, i.e., a
standard bed fumigation with MBC, 67/33, 325 lb/a (rates per bed treated area, which is 58% of total
area), bed fumigation with Pic alone at 200 lb/a, and not fumigated for the current crop. A split-split plot
design was used, with main plots for soil treatments, subplots for individual organisms, and 3
randomized complete blocks. Bare-root Selva transplants were obtained from a high-elevation nursery.
On the day of transplanting, roots and crowns were washed, longer roots trimmed, and 10 plants put into
200 ml of bacterial suspension (>106/ml) for 10 min. Inoculated plants were immediately planted by
normal practice and 30 ml of bacterial suspension added to the soil at each plant. Drip irrigation was
then applied to wet the root zones of transplants. In 1999-2000, inoculated plots were subsequently
divided into two subplots, one which was reinoculated with the same bacterium approximately
bimonthly during plant growth. This was done by adding 100 ml of bacterial suspension to the soil at the
crown of each plant and then irrigating until the root zone was wetted. For each experimental unit, shoot
growth was measured periodically as diameter of ground area covered by leaves. Berries were picked
weekly starting early April through August, sorted for market quality and culls, and weighed. The
incidence of known diseases, such as Verticillium wilt and Phytophthora root or crown rot, was
measured.
Total yields of market quality berries obtained during 2000 are shown in Figure 3. All inoculation
treatments decreased yield on MBC-treated soil, and none increased yield on non-treated soil. On Pictreated soil, however, all the inoculations increased yield and some did so significantly. Periodic
reinoculations during crop growth in 1999-2000 did not enhance the performance of any of the bacteria
used and inoculations were done only once at transplanting in subsequent experiments. Results were
similar in 2000-01 except that only one of the bacteria tested and one commercial isolate of the fungus
Trichoderma harzianum T-22 (8, 11) increased yield on Pic-treated soil (Figure 4). However, while the
inoculation treatments in non-fumigated soil did not increase total yields significantly, three of the
bacterial did reduce the final incidence of plants with symptoms of Verticillium wilt (Figure 5). The
experiment was terminated in August and it is likely that treatments reducing disease at that time would
have enhanced yields obtained later that season using normal practices for the variety Aromas. In 200202 none of the bacteria used in an experiment with MBC-, Pic-, and non-treated soils at MBA increased
the yields of Selva (data not shown). However, in a separate experiment using Aromas on nonfumigated soil, two of the inoculation treatments did increase total yields (Figure 6). Unlike most of the
bacteria used, these specific bacteria (K3, K4) were isolated from plants other than strawberry by C I.
Kado (Plant Pathology, U.C. Davis) and have wide biological activity against plant pathogenic fungi;
they were also applied with a porous bead carrier. While the results obtained at MBA were variable, it
appears that most of the bacterial inoculations of Selva in MBC-treated and nontreated soil reduced
yields while a few of the same inoculation treatments increased yields in Pic-treated soil. The variety
Aromas, however, sometimes responded favorably to bacterial inoculations in non-fumigated soils.
Inoculated Field Plots at Irvine - In cooperation with Dr. Kirk Larson, bacterial inoculations were also
done in replicated field experiments at the U.C. South Coast Research and Education Center (SCREC),
Irvine. The site used in 1999-2000 had a long history of strawberry production and sections were
broadcast fumigated with MBC by standard practices. Two-row beds were subsequently made on
separate fumigated and nonfumigated areas. These were then divided into two experiments and further
subdivided into replicate blocks. Treatments were randomly assigned to plots within individual blocks.
Camarosa was used throughout. Plug plants were propagated by Kirk Larson and conditioned outside at
a high elevation nursery. Bare root plants were produced commercially at the same high elevation
nursery. Bare root and plug plants were both inoculated and transplanted in October, 1999. Plug plants
were placed in inoculum such that the roots and medium were saturated with bacterial suspension at
5
planting. All plants were irrigated by sprinklers immediately after transplanting and periodically
thereafter until sprinklers were replaced by drip irrigation. Inoculated plants were reinoculated with the
same bacteria and plant sizes measured two times as the plants grew. Unfortunately, some plants were
damaged by animals and Santa Ana winds shortly after transplanting, and plug plants survived
somewhat better than bare root transplants. While soil fumigation approximately doubled berry yields in
2000, none of the inoculation or planting material variables modified yield significantly (Figure 7).
The main aspects of the experiments above were repeated in 2000-2001. Ground at SCREC, which was
new to strawberries, was bed fumigated with MBC, Pic, or not treated. Four rhizosphere bacteria
isolated from strawberry were used to inoculate bare-root transplants only at the time of planting. Bed
fumigation with MBC was not very effective, but bed fumigation with Pic increased yield significantly.
This may be due to the more effective distribution of Pic obtained with the drip emulsion application
method, whereas the MBC was shank applied. The relatively small effects of fumigation in this
experiment may also be due to the absence of prior strawberry culture for many years on this site.
Inoculations with 2 bacteria, however, increased growth on nontreated soil, and one bacterium increased
growth significantly on both nontreated and MBC-treated soil (data not shown). Inoculation treatment
effects on yield within any one soil treatment, however, were finally small (data not shown).
A third experiment was done at SCREC in 2001-02. Three soil treatments (MBC, metam sodium @ 30g
a.i./a, and not treated) were applied to ground with a history of strawberries. Yield responses to
fumigation were modest and none of the bacteria increased yields on MBC- or non-treated soils (Figure
8). In contrast, several of the bacteria increased yields on soil treated with metam sodium (Figure 8).
Continuing research
Even though this SAREP project formally ended June 30, 2002, aspects of the research reported here are
continuing. We are continuing to characterize newer isolates obtained in the last year and the most
active of these will be taken to field experiments at MBA in 2002-03 along with some of the isolates
used previously. The continuing research is supported by the California Strawberry Commission.
Potential Benefits/Impacts on Agriculture
Strawberry production in California relies heavily on pre-plant fumigation of soil with methyl bromide,
usually in mixtures with chloropicrin. Currently, the most economically feasible alternatives to methyl
bromide for strawberry production are other chemical fumigants, e.g., Telone with chloropicrin,
chloropicrin alone, and metam sodium (Vapam). Many of the known chemical alternatives are
somewhat less effective or more variable than methyl bromide (e.g. 5-9), and all have risks and some do
not have full registration or public acceptance. While more research is needed to further optimize
chemical alternatives to methyl bromide, the time has come to explore nonchemical options more
scientifically and fully. Nonchemical approaches are needed to supplement chemical alternatives or
possibly replace them in the longer term when used in integrated systems. The introduction of beneficial
microorganisms with transplants is one such approach that can be combined with current practices and,
in the future, with other approaches into less pesticide-intense systems. There is good scientific
precedent for the approach proposed, which is reviewed elsewhere (e.g. 2, 3, 14, 19). The results
obtained so far show some of the potential benefits and pitfalls of using biological agents to help replace
methyl bromide. For example, the beneficial effects of inoculating strawberry with specific bacteria or
fungi were variable between years and locations. Nevertheless, some of our bacteria and one commercial
fungus were beneficial more often than not. Furthermore, the results obtained to date suggest that
bacterial inoculations can be more effective on soils fumigated with metam sodium or low rates of
chloropicrin. Some strawberry varieties (e.g. Aromas) may also be more responsive to beneficial
6
bacteria than others (e.g. Selva). Clearly, the results of this project are still preliminary and more
research is needed to know if and when beneficial bacteria might be used to advantage in commercial
strawberry production.
Dissemination of Findings
Activities and findings of the grant have been or will be reported, in part or fully, at the following
functions: 1999-2000
z
z
z
z
z
z
z
z
July 14, 1999, Research Committee Meeting, California Strawberry Commission, Monterey.
November 1, 1999, Ann. Int. Res. Conf. On Methyl Bromide Alternatives and Emissions
Reductions, San Diego (Literature cited #8).
December 14, 1999, Pest Science Conference, U. C. Davis.
March 2, 2000, Annual Strawberry Conference, Watsonville, CA.
March 22, 2000, California Strawberry Industry Research Conference, SCREC, Irvine.
April 25, 2000, Annual Strawberry Field Day, Santa Maria, CA.
May 16, 2000, California Strawberry Commission Research Workgroup Meeting, Watsonville,
CA.
June 27-28, 2000, Strawberry Methyl Bromide Alternatives Tour, MBA, Watsonville.
2000-01
z
z
z
z
z
z
z
z
z
z
July 12, 2000. Research Committee Meeting, California Strawberry Commission, Monterey, CA.
July 13, 2000. Subcommittee on Livestock and Horticulture of the House Committee on
Agriculture, U.S. House of Representatives, Washington, D.C.
August 14, 2000. Symposium on the status of alternatives to methyl bromide, National Meeting of
the American Phytopathological Society, New Orleans, LA.
September 8, 2000. Strawberry Nursery Meeting, Susanville, CA.
November 6, 2000. Ann. Int. Res. Conf. On Methyl Bromide Alternatives and Emissions
Reductions, Orlando, FL. Literature Cited #6.
January 9, 2001. Seminar at DNA Plant Technology Corp., Oakland, CA.
February 7, 2001. Annual Strawberry Conference, Watsonville, CA.
February 22, 2001. UC DANR Statewide Conference, Riverside, CA.
March 14, 2001, California Strawberry Industry Research Conference, SCREC, Irvine, CA.
June 27, 2001. Strawberry Commission Field Day, MBA, Watsonville, CA.
2001-02
z
z
z
z
z
z
z
z
z
July 18, 2001, Research Committee Meeting, California Strawberry Commission, Monterey, CA.
November 6, 2001, Ann. Int. Res. Conf. On Methyl Bromide Alternatives and Emissions
Reductions, San Diego (Literature cited #7).
December 11, 2001, Sunrise Growers, Oxnard, CA.
January 22, 2002, Annual Strawberry Conference, Watsonville, CA.
January 31, 2002, UC-CE Strawberry Nursery Growers Meeting, Red Bluff, CA.
March 5-8, 2002, International Conference on Alternatives to Methyl Bromide. Sevilla, Spain
(Literature cited #4).
March 13, 2002, California Strawberry Industry Research conference, SCREC, Irvine.
March 27, 2002, Oxnard Strawberry Field Day, Oxnard, CA.
May 15, 2002, California Ornamental Research Federation Methyl Bromide Alternatives School,
7
z
z
z
z
Carlsbad, CA.
June 12, 2002, MBA Strawberry Research Field Day, Watsonville, CA. 2002-03
July 18, 2002, Research Committee Meeting, California Strawberry Commission, Monterey, CA.
July 29, 2002, American Phytopathological Society Annual Meeting, Milwaukee, WI. (Literature
cited #10)
November 6-9, 2002. Ann. Int. Res. Conf. On Methyl Bromide Alternatives and Emissions
Reductions, Orlando, FL. (Abstract submitted)
Literature Cited:
1. Bull, C. and Ajwa, H. 1998. Yield of strawberries inoculated with biological control agents and
planted in fumigated or non-fumigated soil. Abstract 94. Annual International Research Conference on
Methyl Bromide Alternatives and Emissions Reductions, Orlando, Florida. December 7-9.
2. Cook, R. J. 1993. Making greater use of introduced microorganisms for biological control of plant
pathogens. Annu. Rev. Phytopathology 31:53-80.
3. Cook, R. J., and Baker, K. R. 1983. The Nature and Practice of Biological Control of Plant Pathogens.
American Phytopathological Society, St. Paul, MN. 539p.
4. Duniway, J. M., 2002. Non-chemical alternatives used in the USA on horticultural crops. Proceedings
of International Conference on Alternatives to Methyl Bromide. Sevilla, Spain, 5-8 March. Pages 25860. http://europa.eu.int/comm/environment/ozone/conference/
5. Duniway, J. M., Gubler, W. D., and Xiao, C. L. 1997. Response of strawberry to some chemical and
cultural alternatives to methyl bromide fumigation of soil under California production conditions.
Abstract 21. Annual International Research Conference on Methyl Bromide Alternatives and Emissions
Reductions, San Diego, CA. November 3-5.
6. Duniway, J. M., Hao, J. J., Dopkins, D. M., Ajwa, H., and Browne, G. T. 2000. Some chemical,
cultural, and biological alternatives to methyl bromide fumigation of soil for strawberry. Abstract 9.
Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions,
Orlando, FL. November 6-9.
7. Duniway, J. M., Hao, J. J., Dopkins, D. M., Ajwa, H., and Browne, G. T. 2001. Chemical, cultural,
and biological alternatives to methyl bromide for strawberry. Abstract 41. Annual International Research
Conference on Methyl Bromide Alternatives and Emissions Reductions, San Diego, CA. November 5-9.
8. Duniway, J. M., Xiao, C. L., Ajwa, H., and Gubler, W. D. 1999. Chemical and cultural alternatives to
methyl bromide fumigation of soil for strawberry. Abstract 3. Annual International Research Conference
on Methyl Bromide Alternatives and Emissions Reductions, San Diego, CA. November 1-4.
9. Duniway, J. M., Xiao, C. L., and Gubler, W. D. 1998. Response of strawberry to soil fumigation:
microbial mechanisms and some alternatives to methyl bromide. Abstract 6. Annual International
Research Conference on Methyl Bromide Alternatives and Emissions Reductions, Orlando, FL.
December 7-9.
10. Hao, J. J., Duniway, J. M., Dopkins, D. M., and Xiao, C. L. 2002. Effects of rhizobacteria on
inhibition of soilborne pathogens and growth of strawberry. Phytopathology 92:S34 (Abstract).
11. Harman, G. E. 2000. Myths and dogmas of biological control: Changes in perceptions derived from
8
research of Trichoderma harzianum T-22. Plant Disease 84:377-393.
12. Kim, D.-S., Cook, R. J., and Weller, D. M. 1997. Bacillus sp. L324-92 for biological control of three
root diseases of wheat grown with reduced tillage. Phytopathology 87:551-558.
13. Kluepfel, D. A. 1993. The behavior and tracking of bacteria in the rhizosphere. Annu. Rev.
Phytopathology 31:441-472.
14. Linderman, R. G. 1986. Managing rhizosphere microorganisms in the production of horticultural
crops. HortScience 21:1299-1302.
15. Pryor, A. 1999. Results of 2 years of field trials using ozone gas as a soil treatment. Abstract 32.
Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions,
San Diego, CA. November 1-4.
16. Xiao, C. L., and Duniway, J. M. 1998. Bacterial population responses to soil fumigation and their
effects on strawberry growth. Phytopathology 88:S100 (Abstract).
17. Xiao, C. L., and Duniway, J. M. 1998. Frequency of isolation and pathogenicity of fungi on roots of
strawberry in fumigated and nonfumigated soils. Phytopathology 88:S100 (Abstract).
18. Van Loon, L. C., Bakker, P. A. H. M., and Pieterse, C. M. J. 1998. Systemic resistance induced by
rhizosphere bacteria. Annu Rev. Phytopathology 36:453-483.
19. Weller, D. M. 1988. Biological control of soilborne plant pathogens in the rhizosphere with bacteria.
Annu. Rev. Phytopathology 26:379-407.
9
Figure 1. Frequency with which collections of bacterial isolates were found to stimulate the growth of
strawberry seedlings in natural soil under controlled conditions. Collections of isolates were either not
tested for antibiosis or were selected to be antibiosis positive before inoculations to seedlings.
Figure 2. Fresh weights of roots and shoots, and dry weights of roots and shoots (bars in order, left to
10
right, for each isolate), of strawberry plants grown in a greenhouse experiment following inoculations
with individual isolates of bacteria. The average weights per plant are shown for each isolate inoculated
to plants at transplanting (G2, G7, etc.) and non-inoculated controls grown in non-sterile soil (CK2) and
heat-sterilized soil (CK1). The bacteria used had antibiosis to one or more fungi and all inoculations
except G7S were transplanted into non-sterile soil. Weights are expressed as a percentage of that
obtained for non-inoculated controls in non-sterile soil (CK2).
Figure 3. Total berry yields of plants inoculated with individual bacteria at MBA, Watsonville. Yields of
market quality berries were measured as the totals obtained in weekly picks from April through August,
2000. Soil was either fumigated with a standard rate of MBC, with a low rate of Pic, or not fumigated
(NT). Plants were inoculated at transplanting with one of four bacteria designated on the X axis as P1,
P2, P3, or K4, and a subset of each bacterial treatment also received multiple inoculations during crop
growth (red vs. blue bars). There were two noninoculated controls: NT treated with only a buffer; and
K4 treated with carrier without the K4 bacterium (yellow bar). Yields are given relative to that obtained
without inoculation in standard methyl bromide/chloropicrin fumigated soil.
11
Figure 4. Total berry yields of plants inoculated with individual bacteria or a fungus at MBA,
Watsonville. Yields of market quality berries were measured as the totals obtained in weekly picks from
April through August, 2001. Soil was either fumigated with a standard rate of MBC, with a low rate of
Pic, or not fumigated (NT). Plants were inoculated at transplanting with one of five bacteria designated
on the X axis as 1, 3, 4, 5, or 6, and a subset of bacterial treatment 3 also received multiple inoculations
during crop growth (3R). Additional sets of plants were inoculated with the fungus Trichoderma
harzianum strain T-22 or were not treated (NT, green bars). Yields are given relative to that obtained
without inoculation in standard methyl bromide/chloropicrin fumigated soil.
12
Figure 5. Final incidence of plants with visible symptoms of Verticillium wilt on non-treated soil in
August, 2001. This is the same experiment as shown in Figure 4 but only the inoculation treatments
done on non-treated soil are shown.
Figure 6. Total berry yields of Aromas plants inoculated with individual bacteria and grown on non13
fumigated soil at MBA, Watsonville. Yields of market quality berries were measured as the totals
(grams/plant) obtained in weekly picks from April through August, 2002. Plants were inoculated at
transplanting with one of five bacteria designated on the X axis as FP3, FP7, etc. Isolates K3 and K4
were applied with carriers applied separately as treatments K1 and K2, respectively.
Figure 7. Total berry yields of plants obtained in 1999-2000 experiment I at SCREC, Irvine. Relative
yields are given as percentages of the yield obtained with noninoculated, bare-root plants in MBCfumigated soil. Bare root (red bars) and plug plants (blue bars) were inoculated with one of two bacteria
designated on the X axis as P2 and P3 or where not inoculated (NT). Inoculations were done at
transplanting and repeated twice during crop growth. Effects of inoculation treatments within each soil
treatment were not statistically significant.
14
Figure 8. Total berry yields of Camarosa plants inoculated with individual bacteria at SCREC, Irvine.
Yields of market quality berries were measured as the totals obtained in weekly picks from December,
2001, through March, 2002. Soil was either fumigated with a standard rate of MBC, with metam
sodium, or not fumigated (NT). Plants were inoculated at transplanting with one of seven bacteria
designated on the X axis as FP3-9. There were noninoculated controls (CK, red bars) for each soil
treatment. Yields are given relative to that obtained without inoculation in standard methyl
bromide/chloropicrin fumigated soil.
15