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Late Blight Effectively Managed with Resistant Tomatoes on Long Island in 2012

Margaret Tuttle McGrath
Department of Plant Pathology, Cornell University
Long Island Horticultural Research and Extension Center;
3059 Sound Avenue
Riverhead, NY 11901;
mtm3@cornell.edu

and Sandra Menasha
Cornell Cooperative Extension-Suffolk County,
423 Griffing Avenue Suite 100,
Riverhead, NY 11901;
srm45@cornell.edu

 

Additional information about late blight and photographs are posted at:

http://usablight.org/

http://blogs.cornell.edu/livegpath/gallery/tomato/tomato-late-blight/

Results of late blight resistant tomato variety evaluation;conducted in central NY(April 2013)

http://vegetablemdonline.ppath.cornell.edu/factsheets/Potato_LateBlt.htm

http://vegetablemdonline.ppath.cornell.edu/NewsArticles/Tomato_performance_LateBlight_2011.pdf

http://vegetablemdonline.ppath.cornell.edu/NewsArticles/LateBlightFungicidesAug2010.html

Late blight has been occurring routinely on Long Island, starting early in the growing season, and severely impacting tomatoes since 2009.  During the past four years, symptoms have been first seen in late May to mid June.  This disease occurred sporadically before 2009, with symptoms never found or not seen until October in most years.  Change in occurrence of late blight is at least partly due to the fact there are new genotypes (strains) of the pathogen in the USA.  Many are more aggressive on tomato and more tolerant of warm temperatures than genotypes like US-1 and US-8 that previously were dominant.

Resistant varieties are a valuable tool for managing diseases, particularly late blight, because it can be very difficult to control with fungicide applications started after onset and it cannot be ‘tolerated’. Left unmanaged, late blight is much more likely than other diseases to completely destroy a crop and also to have devastating impact on other tomato plantings in a region due to the quantity of pathogen spores that can be produced and easily dispersed by wind.

A replicated experiment was conducted at the Long Island Horticultural Research and Extension Center in 2012 to evaluate new varieties and experimental hybrids that have resistance to late blight in terms of horticultural traits and susceptibility to diseases. Mt Fresh Plus was included as the industry standard for comparison. Most varieties evaluated produce standard red, round, slicer (beefsteak) type fruit.  Plum, cherry, and campari (large cherry) types were also tested.  All named varieties tested are commercially available.  Experimentals from the Cornell Breeding Program also have resistance to early blight and Septoria leaf spot, common foliar diseases occurring in the northeastern USA.

Methods:  The experiment was conducted in a field dedicated to research on organically-produced crops since 2001.  Pro-Grow 5-3-4 organic fertilizer at 2000 lb/A (100 lb/A N) was spread over rows to be planted, then incorporated.  Next drip tape was laid as the rows were covered with black plastic mulch.  Annual ryegrass was planted between rows of plastic mulch to establish a living mulch. 

Tomato seedlings were transplanted by hand on 5 July into holes opened in the plastic mulch by a Waterwheel transplanter that also placed in the holes a starter fertilizer, Neptune’s Harvest Benefits of Fish (2-4-1 N-P-K).  Following standard procedure for fresh-market tomato production on Long Island, plants were staked and trellised as they grew using the Florida weave trellising system with 4-ft stakes placed between plants.

Fungicides approved for organic production were applied to all plots to suppress late blight after finding symptoms in the plots.  The copper fungicide Badge X2 (1.75 lb/A) was applied with Actinovate AG (12 oz/A) on 14 and 22 August, and with Regalia (2 qt/A) on 17 August, 31 August and 7 September.  Sonata ASO (3 qt/A) was also applied on 7 September.  The onset of late blight was considered to be at a time in the growing season that left unmanaged it could adversely affect other experiments and commercial crops nearby.  All applications were made using a tractor-mounted boom sprayer equipped with twinjet nozzles spaced 17 in. apart that delivered 63 gpa at 65 psi. 

Leaves were examined for disease symptoms from 31 July to 12 October.  Severity of symptoms was visually assessed. 

Ripe fruit were harvested on 11, 18, and 27 September and 3 October.   Fruit quality was evaluated by project staff and by 10 public groups, which included growers and gardeners.  Attributes assessed included appearance, taste, and overall quality rated on a 1-5 scale with 5 being excellent.  Yield was not measured for the two entries with cherry-type fruit. 

Results and Discussion:  Very good resistance of foliar symptoms of late blight was exhibited by all tomato varieties and experimental hybrids evaluated that have the Ph2 and/or Ph3 major genes for resistance (Table 1), which were Plum Regal (homozygous Ph3), JTO-545 (heterozygous Ph3), Legend OP (Ph2), Matt's Wild Cherry (undetermined resistance, possibly Ph3), Jasper (undetermined resistance, likely Ph2 and/or Ph3), and Defiant PhR, Mountain Magic, Mountain Merit, and three experimentals from the Cornell University Dept of Plant Breeding (all heterozygous Ph2 + Ph3).  Heterozygous means the hybrid has one copy of the resistance gene; homozygous means it has a copy from both parents which is expected to impart a higher level of resistance.  Iron Lady is a new variety developed at Cornell that is homozygous Ph2 + Ph3.  It is expected to have even better resistance than the others.  High Mowing Organic Seeds is marketing it.  The other resistant varieties are available from Johnny’s Selected Seeds and Seedway.

Late blight became severe in New Yorker (Ph1).  Severity of symptoms was similar to the varieties without major resistance genes, which were Mountain Fresh Plus, Juliet and Brandywine.  The late blight pathogen genotype present in this experiment, US-23, was the dominant genotype present in 2012 in the USA and thus most likely will dominate in 2013.  The Ph1 gene is also not effective for other genotypes of the pathogen that have occurred in recent years.  Thus varieties with only this gene are not recommended.   

Legend, the only entry with just the Ph2 gene, was numerically, but not significantly, more severely affected by late blight than the other resistant entries, except at the last assessment when extensive defoliation may have affected ratings. 

Plum Regal and JTO-545, the two entries with just the Ph3 gene, were numerically more severely affected by late blight than the other resistant entries at all assessments.  The difference was significant at the last assessment (12 October), which was 35 days after the last fungicide application for late blight.  Fungicides applied may have suppressed late blight, especially on resistant varieties, but the late onset of treatment compromised efficacy.

In conclusion, best suppression of the US-23 genotype of the pathogen was achieved with tomato possessing both the Ph2 and Ph3 resistance genes.  Only a few fruit with symptoms of late blight were observed on these entries. 

Mountain Magic, Jasper, and Matt's Wild Cherry were the three resistant varieties receiving the highest overall rating in the 10 evaluations conducted by public groups (Table 2).

Fruit descriptions and assessments for tomato varieties evaluated in 2012:

Mountain Fresh Plus:  Orange to red colored fruit was small and round. Some radial cracking. Flesh was bright red, juicy but acidic and not as sweet. Taste rating of 3 and overall satisfaction 4.

Mountain Merit:  Medium to large, round red fruit. Flesh was sweet but very mealy and soft. Both taste and overall satisfaction rated 3.9 out of 5.

Defiant PhR:  Round, small to medium red fruit. Yellow shoulder on most fruit and some zippering. Flesh was light red to red in color, soft, sweet, juicy, and had good flavor. Lots of seeds. Taste rated 3.5 out of 5 and overall appearance 3.8.

NC123S x CU-TR5:  Medium to large, round fruit has orange to red colored skin. Some zippering. Flesh was bright red, sweet, and had a good flavor. Taste rating of 4.3 and overall satisfaction 4.6.

NC123S x CU-TR3:  Large, orange to red round fruit. Fruit had a white core and red flesh. Slightly chewy skin. Flesh had good flavor and taste but was somewhat mealy. Taste rating of 3.4 and overall satisfaction 3.9.

Brandywine x CU-TR3:  Fruit were round, red and medium in size. Slight yellow shoulder on fruit. Fruit were lacking in flavor and not sweet. Skin was thick. Taste rating of 2.5 and overall appearance 2.8.

Plum Regal:  Plum type with orange to red colored skin. Fruit were medium to big in size. Flesh was mealy and lacking flavor. Taste 2.5 out of 5 and overall satisfaction 3.3 out of 5.

JTO- 545:  Plum tomato, medium in size and red in color. Deep red flash was meaty, slight acidic with a slightly mealy texture. Semi-sweet. Taste rating of 3 and overall appearance rating of 3.5 out of 5.

Mountain Magic:  Small, round red fruit. Campari size. Some cracking of the skin. Flesh was light red, sweet and juicy. Taste rating of 4.6 and overall satisfaction 4.8 out of 5.

Jasper:  Very small, round red cherry tomato. Lots of seeds. Sweet fruit with good flavor. Taste rated 4.6 and overall appearance 4.8.

Matt's Wild Cherry:  Small red cherry tomato. Slightly chewy skin but delicious and super sweet. Taste rating of 4.7 out of 5 and overall appearance 4.8.

Acknowledgments: This project was funded by the Agriculture and Food Research Initiative Competitive Grants Program Grant 2011-68004-30154 from the USDA National Institute of Food and Agriculture.  
A longer report with additional data and photographs is available upon request to mtm3@cornell.edu.

Table 1.  Severity of late blight on tomato varieties and experimental hybrids evaluated in 2012

 

Late blight severity on leaves (%) z

Variety or experimental

Aug 20

Aug 29

Sep 14

Sep 19

AUDPC y

Oct 12 x

Mountain Fresh Plus

75.0

a

52.5

ab

67.5

ab

72.3

ab

2294.4

a

ND

Brandywine

50.5

ab

47.3

ab

76.3

ab

85.0

a

2169.2

a

ND

Juliet

70.0

a

37.8

abc

41.3

bcd

38.9

bcd

1703.6

ab

ND

New Yorker OP

74.3

a

55.6

a

88.8

a

59.5

abc

2522.6

a

ND

Legend OP

26.6

bc

18.9

bcd

42.8

bc

33.5

cde

906.0

bc

32.0

b

Plum Regal

11.3

c

12.7

cd

17.3

cd

13.5

de

428.5

c

81.3

a

JTO- 545 (plum)

18.4

c

11.8

cd

22.0

cd

17.3

de

502.9

c

75.5

a

Mountain Magic

   (campari)

0.3

c

0.1

d

0.1

d

0.1

e

3.2

d

0.0

c

Jasper (cherry)

1.8

c

0.2

d

1.9

cd

0.1

e

25.0

d

17.8

bc

Matt's Wild Cherry

0.2

c

0.3

d

0.1

d

0.1

e

4.6

d

5.8

bc

Mountain Merit

0.2

c

1.9

d

0.1

d

0.2

e

15.0

d

5.0

bc

Defiant PhR

0.2

c

0.2

d

0.6

d

0.0

e

8.9

d

5.5

bc

NC123S x CU-TR5

0.3

c

0.7

d

0.5

d

0.2

e

14.4

d

29.6

b

NC123S x CU-TR3

0.1

c

0.1

d

0.1

d

0.0

e

1.2

d

11.5

bc

Brandywine x CU-TR3

0.0

c

0.1

d

0.1

d

0.0

e

1.3

d

0.3

c

P-value (treatment)

<0.0001

<0.0001

<0.0001

<0.0001

<0.0001

<0.0001

z Numbers in each column with a letter in common are not statistically different from each other.

y Area Under Disease Progress Curve (AUDPC) was calculated for late blight severity from 20 August through 19 September to obtain a measure of severity over multiple assessments.

x ND=not determined because too few leaves remained in plots to assess.


Table 2Combined results of tomato fruit evaluations performed by public groups in 2012. 

Variety or experimental z

Internal

External

Taste

Overall

Would Buy it (%)

Mountain Magic

4.3

abc

4.6

a

4.3

a

4.4

a

89.0

Jasper

4.1

abc

4.3

ab

4.2

abc

4.2

a

84.8

Mountain Fresh Plus

4.4

abc

4.4

ab

4.1

a-d

4.1

abc

80.0

Matt's Wild Cherry

4.1

ab

4.2

ab

4.2

ab

4.1

ab

77.0

Legend OP

3.8

bc

4.2

abc

3.3

b-e

3.7

a-d

66.7

Brandywine x CU-TR3

4.0

abc

4.0

abc

3.6

cd

3.6

bcd

65.4

Juliet

3.0

abc

3.5

abc

2.7

a-e

3.5

a-d

50.0

Plum Regal

3.8

abc

4.0

abc

3.3

de

3.3

cd

55.6

Defiant PhR

3.6

bc

4.0

ab

3.2

de

3.2

d

51.2

Mountain Merit

3.7

bc

4.0

bc

3.4

de

3.2

d

49.4

NC123S x CU-TR3

3.5

c

3.5

c

2.9

e

3.0

d

42.5

JTO- 545 (Plum)

3.7

abc

4.0

bc

2.9

e

3.0

d

44.4

NC123S x CU-TR5

3.7

abc

4.1

ab

2.9

e

2.9

d

33.3

New Yorker OP

3.0

abc

3.5

abc

1.7

de

2.0

a-d

0.0

P-value (variety)

<0.0001

<0.0001

<0.0001

<0.0001

NA

z Entries in table are listed based on overall satisfaction with the fruit.  Fruit quality rated on a 1-5 scale with 5 best.  Numbers within a column with a letter in common are not statistically different from each other.

Following images are of plants in this evaluation on 14 September 2012

Mt. Fresh Plus tomato Brandywine tomato Juliet tomato
Mt Fresh Plus

Brandywine

Juliet

New Yorker tomato Legend tomato Plum Regal tomato
New Yorker

Legend

Plum Regal
Defiant PhR MtMerit MtMagic

Defiant PhR

Mt Merit

Mt Magic

Jasper cherry tomato Matt's Cherry Tomato Brancywine x CU-TR3

Jasper

Matt's Wild Cherry

Brandywine x CU-TR3   

While the resistant varieties performed well, resistance is not immunity, thus some symptoms developed as illustrated below in photographs taken on 14 and 19 September 2012.

Jasper tomato Jasper tomato Matt's Wild Cherry Leaf Matt's Wild Cherry
Jasper   Matt's Wild Cherry