Greenhouse
|
Container.......... |
Bench, pot, or flat deep enough to allow root development |
| Media............... | Sand or soil mixture |
| Temp/Light........ | 24 to 30°C; 16+ hour daylength |
| No. of Plants .... | 35 to 50 per replication |
| No. of Reps....... | 3 replications minimum |
| Other................ | Inoculate with Rhizobium meliloti Dang, encourage vigorous growth |
INOCULUM CULTURE
|
Source.............. |
|
| Storage............. | Inoculated sterile soil cultures or solid PDA medium |
| Temperature....... | 0°C to ambient |
| Storage Life....... | Several years in soil tubes |
INOCULATION PROCEDURE
| Age of Plant...... | 8 to 10 weeks old |
| Type of Inoc....... | Microconidia in suspension |
| Inoc. Culture ..... | Potato or nutrient broth (2 g NaNO3, 1 g KH2PO4, 0.5 g MgSO4-7H2O, 0.5 g KCI, 0.01 g FeSO4-7H2O, 0.5 g yeast extract, and 15 g sucrose per 1 L distilled water); inoculate sterile broth wlth PDA plugs and incubate on a shaker for 4 days at about 21°C |
| Concentration ... | 1.6 X 106 spores per mL or a 1:20 dilution of the shake culture |
| Method ............. | Bare root soak |
| Time of Inoc....... | 20 to 30 min. |
INCUBATION
| Location ........... | Transplant to field |
| Plant Counts .... | Approximately 2 wks after transplanting, count all (alive and dead) plants as the base count for initial stand |
| Culture ............. | Maintain vigorous growth, control insects, clip plants once or twice. |
| Spacing ........... | 0.15 m between plants, 1.0 m between rows. |
| Age at Rating.... | 3 months after transplanting |
RATING
Plants are removed from the field and the tap root
sectioned for rating.
| 0 Resistant ............. | No discoloration in the root |
| 1 Resistant ............. | Small dark strands in the stele |
| 2 Susceptible .......... | Small dark-brown arcs or rings in cross section of the stele |
| 3 Susceptible .......... | Larger dark-brown areas, arcs or rings, or partial dark- brown ring in the outer stele |
| 4 Susceptible .......... | Entire outer stele dark brown, plant alive |
| 5 Susceptible .......... | Dead plant (stand loss) |
CHECK CULTIVARS
| Approximate Expected Resistance (%) | Acceptable Range of Reaction (%) | |
| Resistant | ||
| Agate** | 54 | 45-65 |
| Moapa 69 | 76 | 65-85 |
| Moderately Resistant | ||
| Narragansett | 22 | 15-30 |
| Susceptible | ||
| MNGN-l ** | 4 | 0-8 |
Values for resistant standards are totals of O's and l's.
DISTRIBUTION AND
SEVERITY OF
FUSARIUM WILT
Fusarium wilt, Fusarium oxysporum Schlecht f.
sp. medicaginis (Snyd. & Hans.)
(Click on the map above for a larger version. See
also the KEY)
SOURCE OF INOCULUM AND EXPERTISE
Name ..............Judy A. Thies
Address ...........USDA-ARS
Department of Plant Pathology
495 Borlaug Hall
1991 Buford Circle
University of Minnesota
St. Paul, MN 55108
Phone ..............(612) 625-8240
CULTURE OPTIONS AND RANGE OF CONDITIONS
Mixtures of Fusarium oxysporum and Clavibacter
michiganense subsp. insidiosum inocula will
not influence the severity of Fusarium wilt symptoms, but
it will often produce reduced symptoms of bacterial wilt
(1).
The same procedure can be used in the greenhouse with acceptable accuracy. Plants are inoculated and then trans planted into pots, benchs, or celled flats. Greenhouse evaluations can be rated 6 to 8 wks after transplanting.
INOCULATION OPTIONS
AND RANGE OF CONDITIONS
Eight to 10 week-old plants are lifted from the soil,
washed in tap water, and about 50 plants for each plot
are tied in a bundle. The roots are kept in tap water
until all plants for all plots in a replicate are
prepared. The bundled plants are immersed in the
inoculum, tops trimmed to ca. 4 cm from the crown and the
roots are trimmed to ca. 12 cm length. Roots are kept in
moist paper towel until transplanting.
HELPFUL INFORMATION
If not planted immediately, inoculated plants may be
stored at 3 to 4°C for up to a week. A tobacco planter
or modified vegetable planter works well for
transplanting. It can be expected that many of the highly
susceptible plants will die within 5 to 6 weeks after
inoculation and transplanting. Plants are undercut at 15
cm and roots are sectioned for rating. A carrot or beet
lifter or sod undercutter works wcll for this purpose.
Ratings may be expressed as an ASI or as a percentage
adjusted to the long-time average of the standard check
cultivar. Seed of the susceptible check (MNGN-1) can be
obtained from the USDA-ARS project at the University of
Minnesota.
The primary method used for evaluating resistance to
Fusarium wilt has been a root soak method of inoculation
followed by transplanting to the field and the scoring of
root symptoms about 3 months later (1,2,3).
REFERENCES
1. Frosheiser, F. l., and D. K. Barnes. 1978. Field
reaction of artificially inoculated alfalfa populations
to the Fusarium and bacterial wilt pathogens alone and in
combination. Phytopathology 68:943-946.
2. Frosheiser, F. I., and D. K. Barnes. 1984.In
Standard tests to characterize pest resistance in alfalfa
cultivars. USDA Misc. Publ. No. 1434.
3. Hijano, E. H., D. K. Barnes, and F. I. Frosheiser.
1983. Inhcritance of resistance to Fusarium wilt in
alfalfa. Crop Sci. 23:31-34.