University of Arizona a dot Cooperative Extension

Yuma County Farm Notes

Evaluation of Lettuce Cultivars for Resistance to Fusarium Wilt

Michael E. Matheron1, Barry R. Tickes2, Martin Porchas1, Charles A. Sanchez1, Louis G. Didier3, and Kevin P. Ford4

1The University of Arizona, Yuma Agricultural Center, 6425 W. Eighth Street, Yuma, AZ 85364
2The University of Arizona, Cooperative Extension, 2200 W. 28th St., Suite 102, Yuma, AZ 85364
3Select Seed of Arizona, Inc., 14260 S. Ave. 3E, Yuma, AZ 85365
4Keithly-Williams Seeds, 5 W. 6th St., Yuma, AZ 85364


Abstract

In the 2001-2002 production season, Fusarium wilt was observed for the first time in six different lettuce fields in the Gila and Dome Valley production areas of Yuma County, Arizona. The disease was found in 11 additional sites during 2002-2003. Fusarium wilt presents a serious threat to the health of the lettuce industry in Arizona. The only effective means of controlling Fusarium wilt of lettuce at this time is to avoid infested fields. On the other hand, Fusarium wilt in other crops, such as tomatoes and melons, is controlled effectively by planting cultivars resistant to the pathogen. The relative resistance of lettuce cultivars grown in the Arizona desert production region is unknown; therefore, a cultivar evaluation trial was established in a field known to contain the wilt pathogen, Fusarium oxysporum f.sp. lactucae. Tested cultivars were grouped into three different planting dates: Sep 7, Oct 17 and Dec 6, 2002. A majority of the cultivars within each planting date were those that would be planted in the desert at that time. Fusarium wilt was severe in the early planting of lettuce (Sep 7), moderate in the second planting (Oct 17) and very mild in the third planting (DEC 6). Disease severity was low in some lettuce cultivars in the second planting and most cultivars in the third planting. Among the types of lettuce tested, head lettuce was usually least resistant whereas romaine was most resistant. The data presented in this report are preliminary findings, subject to confirmation in another study planned for the next lettuce production season.

Introduction

In the fall of 2001, a new disease was observed in six different lettuce fields in the Gila and Dome Valley production areas of Yuma County, Arizona. Symptoms included wilting, yellowing of leaves and a red-brown to black discoloration of internal taproot and crown tissue. Affected plants were stunted and often died. This wilt disease affected lettuce plants of all ages, from seedling to mature plant. A Fusarium species was consistently recovered from discolored internal taproot and crown tissue.

Fusarium wilt is new to Arizona lettuce fields; however, the disease was first discovered on this crop in Japan in 1955. The first discovery of Fusarium wilt of lettuce in the United States occurred during 1990 in Fresno County near Huron, California. Most recently, the disease was reported in Italy in 2002. Researchers in Japan named the pathogen Fusarium oxysporum f.sp. lactucae. This fungus is a soil-borne pathogen that can remain viable in soil for many years.

A research paper published in 1993 by Hubbard and Gerik (1) is the current primary source of information concerning the disease cycle and epidemiology of Fusarium wilt of lettuce. Hubbard and Gerik determined in the laboratory that the fungus can grow between 46 and 89 ° F, with optimum growth at 82 ° F. Lettuce was not susceptible to any of the Fusarium wilt pathogens from other crops, including tomatoes and melons. Likewise, no other hosts have been found for Fusarium oxysporum f.sp. lactucae. In seedling inoculation experiments, the researchers found that the lettuce cultivars Autumn Gold, Empire, Excell, Salinas, Vanguard, Vanguard 75, Vanmax, Viva and Winterset were susceptible to the disease in varying degrees, with Salinas demonstrating the most disease tolerance.

Fusarium wilt presents a serious threat to the health of the lettuce industry in Arizona. The only effective means of controlling Fusarium wilt of lettuce at this time is to avoid infested fields. On the other hand, an effective method of managing Fusarium wilt in other crops, such as tomatoes and melons, is by planting cultivars resistant to the pathogen. In the long term, development of lettuce cultivars with resistance to Fusarium oxysporum f.sp. lactucae would be highly desirable. In the short term, we need to evaluate existing lettuce cultivars for their relative susceptibility to the disease. This was initiated this past lettuce production season by establishing a replicated planting of lettuce cultivars in a field known to contain Fusarium oxysporum f.sp. lactucae.


Materials and Methods

A large field trial was established on a commercial lettuce field farmed by Coronation Peak Ranches in Wellton, Arizona. Plots were planted and managed using current commercial practices. Each of the four replicate plots for each head lettuce cultivar contained 600 lettuce plants for a total of 2,400 plants evaluated per cultivar. For romaine and leaf lettuce cultivars, replicate plots each contained 300 plants for a total of 1,200 plants evaluated per cultivar. Tested cultivars were grouped into three different planting dates: Sep 7, Oct 17 and DEC 6, 2002. A majority of the cultivars within each planting date were those that would be planted in the desert at that time. The remainder of the cultivars were included for comparison of disease on the same cultivar within different planting dates or for evaluation of cultivars not grown commercially in the desert. Termination dates for each planting and the number of cultivars of each lettuce type within each planting are listed in Table 1. Disease evaluations were performed three times during crop development in each planting. Only the final disease rating at crop maturity is presented in this report. Each plant within a plot was determined to be diseased if the plant was dead or stunted and displayed the typical wilting and yellowing symptoms of Fusarium wilt of lettuce.

Table 1.

Planting number Planting date Maturity date Days to maturity Number of cultivars tested of each lettuce type.
Head Romaine Greenleaf Red leaf Butter
1 7-Sep 8-Nov 62 41 15 3 4 2
2 17-Oct 11-Jan 86 40 9 4 3 1
3 6-DEC 22-Mar 107 40 4 1 1 1


Results and Discussion

The complete list of tested lettuce cultivars and their respective disease assessments at crop maturity are presented in Table 2. Several cultivars were present in two and occasionally in all three plantings, which allowed for comparison of disease intensity among different planting dates (see Table 3). Among virtually all tested cultivars of lettuce, the severity of disease in the first planting was much higher than that observed in the second planting, which in turn was higher than that observed in the third planting. One possible reason for the differences in severity of Fusarium wilt among planting dates was soil temperature. The average daily soil temperature at the 4-inch depth ranged from 65 to 85°F, 55 to 74°F, and 48 to 64°F for the first, second and third plantings, respectively. In all three plantings, differences in disease severity were detected among the different types of lettuce, with head lettuce being most susceptible whereas romaine demonstrated the highest level of tolerance. Observed disease tolerance for specific cultivars was dependent on disease pressure. Of the 11 head lettuce cultivars tested in both the first (high disease pressure) and second (moderate disease pressure) plantings (see Table 3), the lowest disease rating was a 32% loss in the first planting, whereas three head lettuce cultivars had disease ratings at or below 4% in the second planting. Similar results were observed for romaine, green leaf and red leaf lettuce.

Fusarium wilt was first recognized in the Yuma area during the 2001-2002 season, when Fusarium oxysporum f.sp. lactucae was recovered from diseased head lettuce plants in six different fields. During the just completed 2002-2003 season, the pathogen was recovered from 11 additional head lettuce plantings. Disease was detected in these fields from October through December; therefore, head lettuce fields in production during this time that exhibited no evidence of Fusarium wilt can be assumed to be free of the pathogen. On the other hand, lettuce fields in production during January through March and showing no evidence of Fusarium wilt still may harbor the pathogen, since disease development during this time is greatly reduced and could be overlooked.


Recommendations

Keeping in mind that the data presented in this report are preliminary findings and subject to confirmation by further studies, there are some recommendations that can be made concerning the management of Fusarium wilt of lettuce.

1. Every effort should be made to prevent the spread of contaminated soil from known locations of Fusarium oxysporum f.sp. lactucae to "clean" fields by workers and equipment. These precautions should be maintained even when crops other than lettuce are grown in infested fields.

2. Avoidance. The best way to avoid Fusarium wilt on lettuce is to not plant this crop on sites known to contain the pathogen.

3. Based on the preliminary data presented in this report, one could choose a late planting date (early December) and select a cultivar that sustained little to no disease at this planting time.

4. For the vast majority of lettuce production fields where Fusarium oxysporum f.sp. lactucae is not known to occur, maintain vigilance to prevent the introduction of the pathogen into your fields and use your normal criteria for cultivar and planting time selection.

Acknowledgments

This project was funded by financial support from the Arizona Department of Agriculture, University of Arizona, Arizona Iceberg Lettuce Research Council, Seed Trade Association of Arizona and various commercial lettuce seed producers. We sincerely thank Neil Bowman for allowing us to conduct this trial on his land and Shayne Compton for growing the crop. The authors also wish to thank the Yuma Fresh Vegetable Association as well as the other individuals that were instrumental in planning and implementing this project; all of whom were essential for the successful completion of this study.


Reference

Hubbard, J.C., and Gerik, J.S. 1993. A new wilt disease of lettuce incited by Fusarium oxysporum f.sp. lactucum forma specialis nov. Plant Dis. 77:750-754.

Table 2.  Comparative susceptibility of lettuce cultivars to Fusarium wilt.

Cultivar

Lettuce Type

Producer

% of plants dead or diseased

First planting

Second planting

Third planting

           

Acacia

Head

Synergene

100

-----

-----

Annie

Head

Seminis

100

-----

-----

AZ 90

Head

Central Valley

-----

67

-----

AZ 2000

Head

Central Valley

-----

-----

10

Beacon

Head

Paragon

100

72

-----

Big Green COS

Romaine

Synergene

-----

-----

0

Big Star

Greenleaf

Synergene

-----

0.8

-----

Big Sur

Head

Synergene

-----

-----

0

BOS 9021

Romaine

Orsetti

10

-----

-----

Bubba

Head

Seminis

-----

50

-----

Buccaneer

Head

Central Valley

92

1

0

Cavalier

Head

Progeny

100

-----

-----

Cibola

Head

Paragon

-----

62

-----

Clemente

Romaine

Seminis

14

0.8

-----

Climax

Head

Jim McCreight, USDA

-----

-----

0.1

Coastal Star

Romaine

Coastal

32

2

-----

Cochise 47

Head

Central Valley

-----

59

-----

Colossus

Head

Shamrock

-----

16

-----

Conquistador

Romaine

Seminis

13

0

-----

Coolgreen

Head

Harris Moran

-----

-----

5

Coolguard

Head

Pybas Seeds

-----

41

-----

Connick

Butter

Sun Seeds

-----

66

0.3

Costa Rica #4

Romaine

Jim McCreight

-----

-----

0

Coyote

Head

Seminis

-----

16

-----

Crusader

Head

Progeny

95

-----

0.2

Daneberg 66

Head

Progeny

-----

-----

0.2

Darkland COS

Romaine

Central Valley

20

0.7

-----

Del Oro

Head

Seminis

-----

38

-----

Del Rio

Head

Seminis

-----

6

0

Desert Heat

Head

Central Valley

100

47

11

Desert Queen

Head

Seminis

86

-----

-----

Desert Spring

Head

Seminis

-----

-----

3

Desert Storm

Head

Harris Moran

100

-----

-----

DF 7

Romaine

Pybas

13

0.2

-----

Diamond

Head

Coastal

-----

-----

0

Diamond Back

Head

Central Valley

100

-----

0

Domingos 67

Head

Progeny

-----

-----

0.1


Table 2 (continued).  Comparative susceptibility of lettuce cultivars to Fusarium wilt.

Cultivar

Lettuce Type

Producer

% of plants dead or diseased

First planting

Second planting

Third planting

           

Durango

Head

Coastal

-----

-----

0

Emperor

Head

Harris Moran

100

-----

-----

Encanto

Butter

Synergene

66

-----

-----

EXP 411

Cos/head

Paragon

18

-----

-----

EXP 7542

Head

Paragon

100

-----

-----

EXP 9145

Head

Paragon

100

-----

-----

Fallgreen

Head

Harris Moran

100

-----

-----

Fiorette

Head

Rijk Zwaan

-----

-----

0

Fresheart

Romaine

Orsetti

18

-----

-----

Fortuna

Head

Synergene

100

-----

-----

Gabilan 1315

Head

Paragon

-----

-----

18

Grand Max

Head

Progeny

98

-----

-----

Green Forest

Romaine

Central Valley

26

-----

-----

Green Lightning

Head

Progeny

-----

-----

0.2

Green Pack

Head

Central Valley

70

3

-----

Green Towers

Romaine

Harris Moran

19

-----

-----

Grizzly

Head

Seminis

-----

30

-----

Headmaster

Head

Progeny

-----

-----

0

Heatmaster

Head

3 Star

100

-----

-----

HMX 1527

Head

Harris Moran

-----

-----

4

HMX 1528

Head

Harris Moran

-----

-----

4

Honcho II

Head

Seminis

-----

47

-----

Husky

Head

3 Star

100

16

0.5

Icon

Head

Progeny

-----

-----

0.4

Jackal

Head

Seminis

-----

-----

0.2

Javelina

Head

Seminis

98

-----

-----

Kahuna

Head

Synergene

100

-----

-----

King Louie

Romaine

Paragon

7

0.9

-----

Kofa

Head

Synergene

-----

40

-----

Laguna Fresca

Head

Central Valley

100

-----

-----

La Quinta

Head

3 Star        

82

-----

-----

Lighthouse

Head

Paragon

100

66

-----

Marin

Greenleaf

Orsetti

89

0.8

-----

Milestone

Head

Paragon

100

-----

-----

Mohawk

Head

Seminis

100

-----

-----

Monarch

Head

Paragon

100

-----

-----

Monolith

Head

Shamrock

-----

28

-----


Table 2 (continued).  Comparative susceptibility of lettuce cultivars to Fusarium wilt.

Cultivar

Lettuce Type

Producer

% of plants dead or diseased

First planting

Second planting

Third planting

           

North Star

Greenleaf

Paragon

27

2

-----

Optima

Butter

Vilmorin

86

-----

-----

Palma

Head

Central Valley

100

-----

-----

Paragon PIC

Romaine

Paragon

24

1

-----

Patriot

Head

J. McCreight

-----

-----

0.5

PIC

Romaine

Pybas

29

-----

-----

PRO 1839

Head

Progeny

-----

-----

0

PX 843

Head

Progeny

97

-----

-----

PYB 251

Head

Pybas

-----

-----

8

Raider

Head

Seminis

93

-----

-----

RC 74

Head

Paragon

-----

67

-----

Red Fox

Red leaf

Central Valley

50

2

-----

Red Tide

Red leaf

Seminis

100

88

10

Rivergreen

Head

J. McCreight

-----

-----

0

Robusto

Romaine

Paragon

22

0.9

-----

Sahara

Head

Seminis

100

-----

-----

Salinas 88

Head

J. McCreight

-----

0.8

-----

Sharpshooter

Head

Seminis

32

2

0

Silverado

Head

Coastal

-----

-----

0

Sniper

Head

Seminis

85

4

0

Slugger

Romaine

Coastal

5

0.4

0

Snowbird

Head

3 Star

100

16

0.8

Spector

Head

Seminis

82

-----

-----

Spring Pac

Head

Synergene

-----

-----

0

Sunbelt

Romaine

Central Valley

-----

0.4

0

Sun Devil

Head

Progeny

93

-----

-----

Supercoach

Head

Progeny

-----

40

-----

Syn 352

Head

Synergene

-----

40

-----

Target

Head

Seminis

-----

-----

0.1

Telluride

Head

Coastal

-----

-----

0

Toronto

Head

Rijk Zwaan

-----

-----

0

Tradition

Head

Pybas

100

10

2

Tres Equis

Head

Synergene

98

-----

-----

Triton

Romaine

Harris Moran

16

-----

-----

Two Star

Greenleaf

Orsetti

85

3

0

Valley Green

Head

Harris Moran

100

-----

-----

Valley Queen

Head

Paragon

100

38

-----


Table 2 (continued).  Comparative susceptibility of lettuce cultivars to Fusarium wilt.

Cultivar

Lettuce Type

Producer

% of plants dead or diseased

First planting

Second planting

Third planting

           

Valley Queen +T-22

Head

Paragon

-----

32

-----

Vulcan

Red leaf

Sakata

20

3

-----

Vanguard 75

Head

Jim McCreight, USDA

-----

49

-----

Van Max

Head

Pybas

-----

48

10

Van Mor

Head

Harris Moran

-----

54

-----

Wellton

Head

Paragon

100

-----

-----

Westlands

Head

Orsetti

-----

52

-----

Western Red

Red leaf

Orsetti

39

-----

-----

Wintergold

Head

Progeny

-----

30

-----

Winterhaven

Head

Orsetti

-----

60

-----

Winterhaven BOS

Head

Orsetti

-----

58

-----

Winterking

Head

Paragon

-----

46

-----

Wolverine

Head

Seminis

-----

4

-----

Yuma

Head

Harris Moran

-----

46

-----

# 106

Head

Paragon

-----

-----

6

# 203

Head

Paragon

-----

-----

0.2

3SS106

Head

3 Star

-----

-----

3

           

Least Significant Difference;  LSD (P = 0.05)

5.3

9.3

3.0


Table 3.  Disease assessments on lettuce cultivars tested in
more than one planting date.

Cultivar

% of plants dead or diseased

Sep 7

Oct 17

Dec 6

       

Head lettuce

 

Beacon

100

72

-----

 

Buccaneer

92

1

0

 

Crusader

95

-----

0.2

 

Del Rio

-----

6

0

 

Desert Head

100

47

11

 

Diamond Back

100

-----

0

 

Green Pack

70

-----

3

 

Husky

100

16

0.5

 

Lighthouse

100

66

-----

 

RC 74

67

80

-----

 

Sharpshooter

32

2

0

 

Sniper

85

4

0

 

Snowbird

100

16

0.8

 

Tradition

100

10

2

 

Valley Queen

100

38

-----

 

Van Max

-----

48

10

Mean for head lettuce cultivars tested in multiple planting dates.

 

All three dates

87

14

2

 

First and second dates

89

32

-----

 

Second and third

-----

17

3

 

First and third

87

-----

3

         

Romaine

 

Clemente

14

0.8

-----

 

Coastal Star

32

2

-----

 

Conquistador

13

0

-----

 

Darkland COS

20

0.7

-----

 

DF 7

13

0.2

-----

 

King Louie

7

0.9

-----

 

Paragon PIC

24

1

-----

 

Robusto

22

0.9

-----

 

Slugger

5

0.4

-----

 

Sunbelt

-----

0.4

0

Mean for romaine cultivars tested in multiple planting dates.

 

First and second dates

17

0.8

 

Table 3 (continued).  Disease assessments on lettuce cultivars

 tested in more than one planting date.

Cultivar

% of plants dead or diseased

Sep 7

Oct 17

Dec 6

       

Green leaf

 

Marin

89

0.8

-----

 

Northstar

27

2

-----

 

Two Star

85

3

-----

Mean for green leaf cultivars tested in multiple planting dates.

 

First and second dates

67

2

 
         

Red leaf

     
 

Red Fox

50

2

-----

 

Red Tide

100

88

10

 

Vulcan

20

3

-----

Mean for red leaf cultivars tested in multiple planting dates.

 

First and second dates

 57

 31

 
         

Butter

     
 

Connick

-----

66

0.3


Full Disclaimers

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.

The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.

Any products, services, or organizations that are mentioned, shown, or indirectly implied in this web document do not imply endorsement by The University of Arizona.


Information provided by:
Michael E. Matheron, matheron@ag.arizona.edu Plant Pathologist, Yuma County

University of Arizona, Tucson, Arizona.
Material written June 2003.


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