2003 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 were considered distorted bulbs including those with double necks. 

Seed dealers participating in this trial are listed in Table 1. They specified where each variety would be planted (Delta or Montrose site). Varieties examined but not listed in Table 1 were included at the cooperator's request. The growing season at the Montrose site was 95 - 110 days; the growing season at the Delta county field varies from 110 - 120 days.

Table 1: Varieties included in this trial

Variety	Seed Company	Length of growing Season	Type of Onion
Frontier T‑400	American Takii	97	Export
Tequila (DPS 1062)	Palmer	115-120	Hybrid - Long Day Spanish Yellow
Mesquite (DPS 1063)	Palmer	115-120	Hybrid - Long Day Spanish Yellow
DPSX1171	Palmer	116	Full Spanish
DPSX1172	Palmer	116	Full Spanish
Gunnison	Bejo
BGS 167	Bejo
Delgado	Bejo	125	Spanish Storage
Expression	Bejo	98	Intermediate
Seahawk	Seminis	114	Spanish Storage
15192	Seminis	110	Spanish Storage?
Golden Spike	Seminis	103	Intermediate
Tioga	Seminis	118	Spanish Storage
Genesis	Crookham	95-100	Yellow Northern Storage hybrid
OLYH99-2900	Crookham
Sweet Perfection	Crookham	120-125	Golden Brown Spanish hybrid
Granero	Sunseed	115-118	Long Day (Spanish Type)
Sabroso	Sunseed	110-115	Long Day (Hard Globe Western Type)
Tesoro	Sunseed	110-115	Long Day (Spanish Type)
EM 635	Emerald Seed
EM 702	Emerald Seed

A randomized complete block design was utilized in this study. Each variety was replicated four times.   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.  A bed ten feet in length (with two lines of onions) beginning 5 feet from the head of the plot was selected from each plot for this evaluation.

Planting was done at the Delta County and Montrose County sites on April 5 and March 31, respectively.  Coated seed was planted with cooperator's equipment; uncoated seed was planted by hand. The Montrose plots were harvested on September 5; the Delta plots on September 8. 

Each Delta County plot was scouted twice during the season and data collected on fusarum-infected plants and bulbs. Infected plants and bulbs were pulled and removed from the site. No Fusarium-infected bulbs were located at the Montrose site during the growing season. Data were collected from two eight-foot lines of onions collected from each plot.   

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 analytical purposes, data from both lines of onion were averaged for each plot.  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 the time of harvest and the total percent of bulbs for the Delta site.  The percentage of infected bulbs based on the total number of bulbs is provided.  No significant differences in fusarium basal plate rot susceptibility were found at the Delta site.

The Homewood site had a very low level of FOC-infected onion bulbs (data not shown).

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 3 provides the Homewood cull data.

Acknowledgments:

Without the help of Jerry Hines and Duane Homewood and their staff these plots would not have been possible. They were responsible for planting, cultivation, irrigation and many other tasks. Tri River Area Master Gardeners devoted considerable time assisting in planting, harvesting and collecting data. American Takii, Inc. , D. Palmer Seed CO. , Inc. , Bejo Seeds, Inc., Seminis Vegetable Seeds, Sunseed, Emerald Seed,and Crookham Company provided seed and financial support for these trials. Financial support and encouragement was also provided by the Colorado Onion Association.

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	% of Fusarium-infected bulbs per plot at harvest	Total % of Fusarium-infected bulbs removed from each plot
Tequila	0.7	3.1
Mesquite	2.1	3.7
DPSX 1171f	2.3	8.5
DPSX 1172	3.7	10.3
Seahawk	0.8	23.5
Tioga	0.3	0.6
15192	0.8	10.1
Golden Spike	1.1	6.4
Sweet Perfection	1.1	1.4
Harmony	0.8	1.9
Gunnison	1.1	33.5
Delgado	1.6	8.1
BGS167	1.2	9.8
Sabroso	2.5	7.9
Tesoro	0.7	8.0
Granero	1.5	21.0
LSD	ns	ns

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

Variety	Cull bulbs per plot	% of cull bulbs compared to total bulbs harvested per plot
Genesis	0.4	0.0
OLYH99-2900	0.5	0.5
Expression	0.3	0.6
Gunnison	0.7	1.1
Frontier	0.0	1.0
EM 635	0.0	0.0
EM 702	1.0	0.6
Delgardo	1.3	0.0
LSD	ns	ns