2003 Western Colorado Onion Variety Trials

Pink Root Study

 

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

Purpose:

Pink root, caused by Phoma terrestris E. M. Hans. [syn. Pyrenochaeta terrestris (E. M. Hans. ) Gorenz, J. C. Walker & R. H. Larson], is one of the most devastating diseases of onions grown in warm climates (Schwartz and Mohan, 1995, pg. 12) and is a wide-spread problem of onions in Colorado (Everts, 1984, pg. 3. ). In this study 21 varieties were examined to determine their susceptibility/resistance to this disease.

Materials and Methods:

Two commercial onion fields farmed by Jerry Hines (Delta County) and Duane Homewood (Montrose County) were used in this study. These fields varied in their soil types (silty clay loam vs. a soil of a sandy consistency respectively), and history of P. terrestris contamination. The Hine’s field has a history of a higher percentage of pink root than the Homewood field.

Seed dealers participating in this trial are listed in Table 1. They specified where each variety would be planted (Delta or Montrose site). 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 with each variety replicated four times. Plots were 35 feet long; two lines of the same variety of onion were planted on each bed. Beds were 30 and 34 inch on center at the Homewood and Hines fields, respectively.

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. 

All onions in an eight-foot lineal space (two lines of onions) were hand-dug from each line of onions in each plot and graded as to the percentage of roots infected by the pink root organism (as determined by color).The average percentage of infection for the resulting sixteen feet of row was analyzed using MSTAT-C, the Michigan State MicroProcessor Statistical Program.

Past experience indicated pink root infections occur in pockets in the field/row. Harvesting all bulbs in a continuous section of row is felt to be a more realistic test of the amount of infection present than harvesting bulbs at random throughout the plot.

The statistical difference of susceptibility to P. terrestris is indicated in Table 2 by the letter(s) that follow the percentage of infection. Percentages followed by the same letter are statistically identical in regard to incidence of pink root. In this trial, "a" following the percentage of pink root indicates the higher level of infection; "g" in Field #1, and "c" in field #2 following a percentage indicates the lowest level of infection.

Table 2: Percentage of Pink Root in Field #1 and Field #2

Field #1: Hines, Delta County		Field #2: Homewood, Montrose County
Variety	Percentage of Pink Root	Variety	Percentage of Pink Root
Gunnison	52.48 a	Expression	17.06 a
Delgado	39.84 ab	EM 702	15.47 a
Seahawk	37.38 abc	Gunnison	13.78 ab
15192	28.71   bcd	Delgado	13.57 ab
DPSX 1171	25.83   bcde	Genesis	5.73  bc
Golden Spike	23. 20    cdef	OLYH99-2900	5.40    bc
DPSX 1172	20. 95     defg	Em 635	5.12   bc
Sabroso	16.95      defg	Frontier	4.06      c
Granero	12.54        efg
Harmony	12.14        efg
Tesoro	11.85        efg
Sweet Perfection	11.05        efg
Tequila	10.32        efg
Mesquite	9.53          fg
Tioga	8.22          fg
BGS 167	6.06            g
LSD	16.08  0. 05	LSD	8.92  0. 05

Results:

Table 2 shows the percent infection of each variety examined ranged from a high of 52.5 to a low of 4.1 in the two fields, with the Delta county field having the higher infection rates. The highest level of infection in the Montrose county field was 17.1%.

Discussion:

Data collected in 2003 indicate varietal differences in susceptibility to the pink root organism. Varieties that appear more resistant and having qualities of size and harvest date preferred by the grower should be selected for planting in fields known to have a history of P. terrestris contamination.

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:

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

Everts, K. L. 1984. Masters Thesis: Epidemiology and Management of Fusarium Basal Rot and Pink Root Diseases of Onions. Colorado State University, Fort Collins, CO