PERFORMANCE OF ONION VARIETIES IN A FIELD WITH HIGH

IRIS YELLOW SPOT VIRUS PRESENCE

 

 

Clinton C. Shock, Erik B. G. Feibert, and Lamont D. Saunders

Malheur Experiment Station

 Oregon State University

Ontario, OR, 2009

 

 

Introduction

 

Onion plants infected with iris yellow spot virus (IYSV) can progressively lose leaf area, resulting in reduced yield and reduced bulb size. The IYSV is transmitted by onion thrips (Thrips tabaci).  The incidence of IYSV can be increased by inadequate control of onion thrips.  Thrips control has been complicated by their increasing resistance to pyrethroid and organophosphate insecticides. 

 

A certain degree of varietal tolerance to thrips and IYSV is suggested by the results of the yearly onion variety trials conducted at the Malheur Experiment Station (Shock et al. 2007).  The severity of IYSV infestation in these trials is often low or modest and varies from year to year.  A severe IYSV infestation has occurred consistently each year in onion fields in an area approximately 10 miles to the east of the experiment station.  A subset of the onion varieties in the station trial was evaluated in a commercial onion field in the area of high IYSV severity in 2009.

 

Materials and Methods

 

Onion seed of 12 varieties was planted in double rows spaced 3 inches apart at 9 seeds/ft of single row on April 8.  Each double row was planted on beds spaced 22 inches apart. Planting was done with customized John Deere Flexi Planter units equipped with disc openers.  On June 2, the seedlings were hand thinned, as closely as possible, to a plant population of 2 plants/ft of single row (6-inch spacing between individual onion plants equivalent to 95,000 plants/ac).   

 

On July 31 and August 24, onions in each plot were evaluated subjectively for severity of symptoms of iris yellow spot virus (IYSV).  Twenty consecutive plants in a row in each plot were rated on a scale of 0 to 5, where 0 = no symptoms, 1 = 1 to 25 percent of foliage diseased, 2 = 26 to 50 percent of foliage diseased, 3 = 51 to 75 percent of foliage diseased, 4 = 76 to 99 percent of foliage diseased, and 5 = 100 percent of foliage diseased.  Onions from 23 ft of the middle 2 rows in each plot were topped by hand and bagged on August 24.

 

The onions were graded on September 10.  During grading, bulbs were separated according to quality: bulbs without blemishes (No. 1s), split bulbs (No. 2s), neck rot (bulbs infected with the fungus Botrytis allii in the neck or side), plate rot (bulbs infected with the fungus Fusarium oxysporum), and black mold (bulbs infected with the fungus Aspergillus niger).  The No. 1 bulbs were graded according to diameter: small (<2.25 inches), medium (2.25-3 inches), jumbo (3-4 inches), colossal (4-4.25 inches), and supercolossal (>4.25 inches).  Bulb counts per 50 lb of supercolossal onions were determined for each plot of every variety by weighing and counting all supercolossal bulbs during grading.

 

After grading, bulbs from each plot were rated for single centers.  Twenty-five consecutive onions ranging in diameter from 3.5 to 4.25 inches were rated.  The onions were cut equatorially through the bulb middle and, if multiple centered, the long axis of the inside diameter of the first single ring was measured.  These multiple-centered onions were ranked according to the inside diameter of the first single ring: small had diameters less than 1.5 inches, medium had diameters from 1.5 to 2.25 inches, and large had diameters greater than 2.25 inches.  Onions were considered "functionally single centered" for processing if they were single centered or had a small multiple center.

 

Results and Discussion

 

Bulb yields were low over all varieties, probably due at least in part to late planting and heavy virus presence.  Varieties ‘Charismatic’, ‘Swale’, and ‘Affirmed’ were among those with the highest total and marketable yield (Table 1).  ‘Arcero’, ‘Joaquin’, ‘OLYX06-25’, and ‘Granero’ were among the varieties with the highest percentage of single-centered bulbs (Table 2).

 

‘The Rock’, Charismatic, and Joaquin were among those with the lowest severity of symptoms of IYSV (Table 2). 

 

References

 

Shock, C.C., E.B.G. Feibert, L.D. Saunders, L. Jensen, and K. Mohan. 2007. 2006 Onion Variety Trials. Oregon State University Agricultural Experiment Station Special Report 1075:33-42.

 

Acknowledgements

 

This project was partially funded by the Western Sustainable Agricultural Research and Education Program, the Idaho-Eastern Oregon Onion Committee, cooperating onion seed companies, Oregon State University, University of Idaho, and Washington State University.

 

 

 

 

 

 


Table 1. Yield, and grade of onion varieties planted in a field with high iris yellow spot virus incidence, Malheur Experiment Station, Oregon State University, Ontario, OR, 2009.

 

 

Total yield

Marketable yield by grade

 

Non-marketable yield

Bulb counts >4¼ in

Seed company

Variety

Total

>4¼ in

4-4¼ in

3-4 in

2¼-3 in

 

No. 2s

Small

Total rot

 

 

---------------------- cwt/acre -----------------------

 

-- cwt/acre --

%

#/50 lb

D. Palmer

Evolution

398.2

376.9

0.0

17.6

280.3

79.0

 

5.7

14.0

0.3

 

Nickerson-Zwaan

Ringleader

306.1

284.9

1.8

27.8

196.6

58.7

 

2.8

14.2

1.7

16.0

Crookham

The Rock

389.8

376.4

0.0

4.6

302.3

69.5

 

0.0

13.4

0.0

 

 

OLYX06-25

358.1

320.3

0.0

1.9

215.1

103.3

 

3.4

28.8

1.9

 

Nunhems

Arcero

315.1

291.9

0.0

0.0

169.8

122.1

 

1.6

19.4

0.8

 

 

Granero

426.5

412.3

0.0

3.6

343.0

65.8

 

4.6

8.0

0.5

 

 

Joaquin

315.8

298.4

0.0

2.6

226.5

69.3

 

6.4

11.0

0.0

 

 

Vaquero

403.0

395.8

0.0

11.0

320.6

64.1

 

0.0

7.3

0.0

 

Seminis

Affirmed

433.8

408.0

0.0

6.8

329.7

71.5

 

8.4

12.1

1.6

 

 

Charismatic

489.5

473.1

8.2

55.3

360.1

49.5

 

7.8

12.8

0.6

14.2

 

Monarchos

373.8

347.9

0.0

16.9

265.0

66.0

 

5.1

13.7

2.1

 

 

Swale

440.0

419.9

0.0

0.8

349.3

69.8

 

8.4

7.4

0.9

 

 

Average

387.5

367.1

0.8

12.4

279.9

74.0

 

4.5

13.5

0.9

15.1

 

LSD (0.05)

98.6

94.4

NS

28.8

84

NS

 

NS

NS

NS

NS

 

 

 

Table 2. Onion bulb multiple-center and iris yellow spot virus (IYSV) ratings, Malheur Experiment Station, Oregon State University, Ontario, OR, 2009.

Seed company Variety Maturity Aug. 24 Multiple center   Single center  
Large Medium Small   Functionala Bullet IYSVb
    ----------------------------------- % ------------------------------------- 0 - 5
D. Palmer Evolution 44.0 0.8 3.2 12.0 96.0 84.0 3.2
Nickerson-Zwaan Ringleader 42.5 1.0 9.0 12.0 90.0 78.0 3.5
Crookham The Rock 32.0 0.8 9.6 14.4 89.6 75.2 2.6
OLYX06-25 42.0 0.0 0.8 12.0 99.2 87.2 3.4
Nunhems Arcero 50.0 0.0 2.4 8.0 97.6 89.6 4.2
Granero 51.0 3.2 0.8 9.6 96.0 86.4 4.0
Joaquin 41.0 2.4 3.2 7.2 94.4 87.2 3.0
Vaquero 54.0 0.8 4.0 16.0 95.2 79.2 4.0
Seminis Affirmed 52.0 1.6 4.0 19.2 94.4 75.2 3.6
Charismatic 41.7 4.7 5.3 21.3 90.0 68.7 2.8
Monarchos 43.0 3.2 1.6 14.4 95.2 80.8 3.2
Swale 47.0 0.8 7.3 29.8 91.9 62.1 3.4
average 45.0 1.6 4.3 14.7 94.1 79.5 3.4
LSD (0.05) 6.6 NS NS NS   NS NS 0.6
abullet single center + small multiple center.

a bullet single center + small multiple center.

b IYSV: 0 = no symptoms; 1 = 1-25% of foliage diseased; 2 = 26-50% of foliage diseased; 3 = 51-75% of foliage diseased; 4 = 76-99% of foliage diseased; and 5 = 100% of foliage diseased.