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Cucurbit Genetics Cooperative Report 6:35-37 (article 17) 1983

Resistance of Cucumber to the Pickleworm

Todd C. Wehner, George G. Kennedy and Kent D. Elsey

North Carolina State University, Raleigh, NC 27650 (first and second author); United States Dept. of Agriculture, Vegetable Laboratory, Charleston, SC 29407 (third author)

Pickleworm (Diaphania nitidalis Stoll.) is one of the three most important insect pests of pickling cucumber (Cucumis sativus L.) in the southern U.S.A. Cucumbers have been tested for pickleworm resistance by several researchers (1, 2, 3, 4, 5), and some lines have been identified as having some resistance. However, the resistance was not demonstrated to be horticulturally useful.

Control of pickleworm is useless unless done before the larvae become established in the fruit. Genetic resistance, therefore, would be most effective if it acted to prevent oviposition by adult females, or feeding by larvae. We determined that antibiosis to larvae would be the easier trait to test and to select for, so a detached leaf test was developed. The objectives of this study were to develop a test for detached leaves of cucumber for pickleworm antibiosis, and to screen cucumber lines for leaf antibiosis using pickleworm larvae.

Preliminary Test. A preliminary test was used to determine the optimum conditions for running a detached leaf test using field-grown plants and first instar pickleworm larvae. We determined that the test should be run using 2 ml of distilled water added to 2 layers of filter paper in 100 mm diameter petri plates to which 1 cucumber leaf and 5 pickleworm larvae were added. The leaf was folded with the abaxial side in, and the larvae placed inside the folded leaf.

Field Test. Cucumber lines were obtained from as many sources as possible to make a collection of 1160 cultivars and breeding lines of pickling and slicing cucumbers (including the U.S. plant introduction collection). The lines were planted May 27, 1981 at Clinton, NC and leaves were harvested June 23 and July 14. The youngest fully-expanded leaf was harvested from one plant in each plot on each harvest date, placed in a plastic bag, and stored in a cooler. The following day, leaves were placed in petri plates with larvae and kept at room temperature for 5 days. Leaves were scored for pickleworm feeding damage using a scale of 1 to 9 (1 = no damage, 9 = completely eaten between leaf veins).

Laboratory Studies. Of the 1160 lines tested, the 18 most resistant and 18 most susceptible were retested in Charleston, SC using several laboratory tests. The tests were run in Fall, 1981, and consisted of a detached leaf test and a preference test.

Detached Leaf Test. A leaf was selected from the upper third of each plant of each entry (usually 10 plants/entry), trimmed to an area of approximately 100 cm2, and placed on a moist piece of filter paper in a 100 mm x 15 mm plastic petri plate. Six newly-hatched pickleworm larvae were placed on the abaxial surface of the leaf; the plate was closed and secured with a strip of parafilm around the plate. Plates were held at 24°C, and after 6 days, were opened to count the larvae and score the leaves for damage (using the scale 1 to 9).

Preference Test. A 28 mm leaf disc of each line to be tested was laid on moist filter paper in a petri dish next to similar piece of leaf from ‘Columbia’ (the check cultivar). The leaf circles were 12 mm apart, and in this space were placed 5 newly-hatched larvae. Ten plates were prepared for each test, and were wrapped with parafilm. After 24 hrs. the larvae on each leaf circle were counted. A X2 test was used to determine if an entry was significantly less preferred.

Results. Of the 1160 lines tested in the initial (2-replication) screening test, 36 were selected for retesting in the laboratory at Charleston (18 resistant and 18 susceptible). Of those, 8 were selected for further studies (5 resistant and 2 susceptible). The 8 selected lines, and their performance in the pickleworm resistance tests, are shown in Table 1. Correlations among the 3 tests were high, but not always statistically significant because of the small number of lines involved. Of particular interest is the large negative correlation between the detached leaf and preference tests (r = -0.70). That indicates that lines with some leaf antibiosis tended to be preferred over the check line in the preference test. The 8 lines will be retested in the lab and field to verify their resistance or susceptibility and to further refine the lab test.

Table 1. Performance of 8 selected cucumber lines in 2 antibiosis tests and 1 preference test.


Rank

Cultivar or line

Seed source

Detached-leaf
test scorez

Preference
testy

Line
classificationx

Clinton

Charleston


   1

C541 C2

Joseph Harris Co.

3.0

3.1

54

R

   2

Femscore

VanderPloeg

3.0

3.2

37

R

   3

PI 205996

Sweden

3.0

3.2

55

R

   4

RS 79031

Royal Sluis

3.0

3.3

53

R

   5

Earlipik 14

Northrup-King Co.

3.5

1.5

56

R

1158

MSU 581 H

Mich. State Univ.

5.5

5.0

40

S

1159

PI 263079

USSR

6.5

4.3

42

S

1160

VDP No. 328

VanDerPloeg

6.5

4.5

39

S


zLeaf damage scored 1 to 9 (1 = no damage, 9 = leaf tissue between veins completely eaten).

yPercent of larvae on test line (remainder are on the check cultivar, Columbia).

xR = resistant, S = susceptible.

Literature Cited

  1. Lower, R. L. 1971. Screening cucumbers for resistance to cucumber beetle and pickleworm. HortScience 6:276 (Abstr.).
  2. Quisumbing, A. R. and R. L. Lower. 1975. Screening cucumber cultivars for pickleworm resistance. HortScience 10:147 (Abstr.).
  3. Pulliam, T. L., R. L. Lower, and E, V. Wann. 1979. The effects of cucumber plant type and morphology on infestation by the pickleworm. HortScience 14:120 (Abstr.).
  4. Pulliam, T. L., R. L. Lower, and E. V. Wann. 1979. Investigations of the effects of plant type and morphology of the cucumber on infestation by the pickleworm, Diaphania nitidalis Stoll. Cucurbit Genetics Coop. Rpt. 2:16–17.
  5. Wann, E. V., J. F. Robinson, R. L. Lower, J. M. Schalk and T. L. Pulliam. 1978. Screening cucumbers for resistance to pickleworm. Cucurbit Genetics Coop. Rpt. 1:16.
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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
Created by T.C. Wehner and T. Ng, 1 June 2005; design by C.T. Glenn;
send questions to T.C. Wehner; last revised on 23 October, 2009