2002 Western Colorado Onion Variety Trials

Fusarium Basal Plate Rot and Culls

Dr. Curtis E. Swift, Area Extension Agent (Horticulture) and A. Wayne Cooley, Extension Agent (Soil and Crop Science) (deceased)

Purpose:

Fusarium oxysporum Schlectend. emend.:Fr. f. sp. cepae (H.N. Hans.) W.C. Snyder & H.N. Hans, the causal agent of Fusarium basal plate rot of onion is of concern wherever onions are grown (Schwartz and Mohan, 1995; Common Names).  Up to 90% loss of seedlings and 30% loss of stored bulbs have been reported (Entwistle, 1990).  Colorado onion fields are not immune to this pathogen. In 1920, serous losses in onion fields near Grand Junction and Delta, Colorado and subsequent very heavy losses of stored onions due to this pathogen were reported (Link and Bailey, 1926).

This research was conducted to determine differences in Fusarium oxysporum cepae (FOC) susceptibility among onion varieties.  This data is of special value to onion growers planting into FOC-contaminated fields and breeders trying to develop FOC-resistant varieties.

Data on culls is also important to growers since loss due to culls reduces profits.  In this research, culls are considered distorted bulbs including those with double necks. 

Table 1: Varieties included in this trial

Variety	Seed Company	Length of growing Season	Type of Onion
Eagle T‑406	American Takii	117	Spanish Storage
Frontier T‑400	American Takii	97	Export
T‑441	American Takii	107	Hard Globe
T‑439	American Takii	107	Full Spanish
T‑418	American Takii	97	Export
Husky X302	Palmer	90	Hard Globe
DPS1169	Palmer	92	Hard Globe
DPSX 1170	Palmer	112	Spanish storage x hard globe
Kodiak X400	Palmer	112	Spanish storage x hard globe
DPSX1171	Palmer	116	Full Spanish
DPSX1172	Palmer	116	Full Spanish
Expression	Bejo	98	Intermediate
BGS‑142	Bejo	105	Export
Prince	Bejo	105	Export
Delgado	Bejo	125	Spanish Storage
Legend	Bejo	125	Spanish Storage
Daytona	Bejo	120	Spanish Storage
Seahawk EX‑15232	Seminis	115	Spanish Storage
Kingfisher EX‑15120	Seminis	117	Spanish Storage
Super Chief EX‑77031	Seminis	115	Full Spanish
Tioga	Seminis	115	Spanish Storage
Varsity	Seedworks	105	Spanish Storage
Raptor	Seedworks	118	Full Spanish
Xph95345	Crookham	115	Spanish Storage

A randomized complete block design with each variety replicated four times was utilized in this study.   Plots were 35 feet in length with two lines of the same variety of onion planted per bed. Bed spacing was 30 and 34 inches for the Montrose and Delta sites, respectively. 

Planting was done at the Delta County and Montrose County sites on March 29 and April 1, respectively.  Coated seed was planted with cooperator's equipment; uncoated seed (provided by D. Palmer Seed Co., Inc.) was planted by hand. The Montrose plots were harvested on September 16; the Delta plots on September 19. 

Data were collected from two ten-foot lines of onions between 5 feet and 15 feet from the head of each plot. The number of bulbs and total bulb weight in kilograms was recorded for Colossal-, Jumbo-, Medium-, and Prepack/Boiler-size onion bulbs.   A grading table provided by Dr. Howard Schwartz, Professor, Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO, was used to delineate bulb size. For analysis purposes, data from both lines of onion were averaged for each plot and converted to hundredweight per acre (CWT/A).  MSTAT-C, the Michigan State MicroProcessor Statistical Program, was used for all statistical analyses.

Results/Discussion:

Table 2 provides data on bulbs infected with Fusarium basal plate rot at harvest for the Hines site.  The percentage of infected bulbs based on the total number of bulbs is also provided.  Significant differences (P=0.01) were found with both comparisons at the Hines (Delta County) site.

Percentages followed by the same letter are statistically identical in regard to Fusarium infection.  In this trial, "a" indicates the greatest number of bulbs infected at harvest and the greatest percentage of bulbs infected when compared against the total number of bulbs harvested.

The Homewood site had a very low level of FOC-infected onion bulbs (data not shown). Differences among varieties within plots (P=0.22) or when compared with the total number of bulbs harvested (P=0.11) were too small to consider significant.

There were no significant differences among varieties for the average number of cull bulbs per plot or the percentage of culls based on the total number of bulbs harvested at the Hines site (data not shown).  Comparisons among the varieties for cull bulbs at the Homewood site were, however, significant.  Table 4 provides the Homewood data.

Growers and seed companies should consider these findings when choosing or recommending onion varieties for areas with a high incidence of Fusarium basal plate rot caused by Fusarium oxysporum f. sp. cepae.

Acknowledgments:

These trials would not have been possible without seed and the financial support provided by American Takii, Inc., D. Palmer Seed CO., Inc., Bejo Seeds, Inc., Seminis Vegetable Seeds, SeedWorks, and Crookham Company. The Colorado Onion Association also provided financial support and encouragement.  Jerry Hines (Delta County) and Duane Homewood (Montrose County) and their staff were responsible for planting and general maintenance.  Tri River Area Master Gardeners assisted in the planting, harvesting and data collecting process.

References:

Common Names of Plant Diseases, APSNet. The American Phytopathological Society.

Entwistle, A.R. 1990. Root Diseases. Pp. 103-154, in: Onions and Allied Crops. Volume II. Agronomy, Biotic Interactions, Pathology, and Crop Protection. Rabinowitch, H.D., and Brewster, J.L., eds. CRC Press, Boca Raton, FL.

Link, G.K.K. and Bailey, A.A. 1926. Fusaria causing bulb rot of onions. Journal of  Agricultural Research. Volume 33, No. 10. Pp. 929-952.

Schwartz, H.F., and Mohan, S.K. 1995. Compendium of Onion and Garlic Diseases. APS Press, St. Paul, MN.

Table 2: The incidence of Fusarium Basal Plate Rot at the Hines Site (Delta County, Colorado)

Variety	Fusarium-infected bulbs per plot at harvest	% of Fusarium-infected bulbs compared to total bulbs harvested per plot
Seahawk	3.75  bcd	0.093  bcd
Kingfisher	1.75  d	0.041  cd
Super Chief	2.00  cd	0.047  cd
Tioga	2.50  bcd	0.064  cd
Kodiak	5.50  bc	0.176  b
DPSX 1171	3.00  bcd	0.068  cd
DPSX 1172	2.25  bcd	0.063  cd
Delgado	5.50  bc	0.112  bcd
Legend	4.50  bcd	0.128  bc
Daytona	2.00  cd	0.078  cd
Varsity	11.25  a	0.274  a
Raptor	2.25  bcd	0.056  cd
XPh95345	3.25  bcd	0.076  cd
Eagle	3.50  bcd	0.089  bcd
T-441	3.00  bcd	0.136  bc
Ranchero	1.00  d	0.024  d
Granero	5.75  b	0.118  bcd
LSD	3.68  0.01	0.095  0.01

Table 3: Cull - Homewood Site (Montrose County, Colorado)

Variety	Cull bulbs per plot	% of cull bulbs compared to total bulbs harvested per plot
Husky	1.75  b	0.07  a
DPS 1169	0.50  bc	0.01  b
DPSX 1170	0.50  bc	0.01  b
Expression	3.75  a	0.07  a
BGS-142	0.25  bc	0.02  b
Prince	0.25  bc	0.00  b
Varsity	0.25  bc	0.01  b
Frontier (T-400)	0.00  c	0.00  b
T-418	0.00  c	0.00  b
T-439	0.75  bc	0.01  b
Teton	1.00 bc	0.02  b
LSD	1.64   0.01	0.03  0.05