Cucurbit Genetics Cooperative
Other Crop Genetics Cooperatives
Home About Membership Reports Gene Lists Conferences Links Search NCSU
Cucurbit Genetics Cooperative Report 8:2-3 (Article 1) 1985

Segregation of the Determinate (de) Allele in Crosses Between Cucumis sativus L. and C. sativus var. hardwickii (R.) Alef.

D.E. Delaney and R.L. Lower

University of Wisconsin, Madison, WI 53706

In 1982, we initiated a breeding program for increasing the number of lateral branches on determinate plant types. The objective was to alter the plant architecture of current determinate lines by incorporating the multiple lateral branching character from Cucumis sativus var. hardwickii. The new plant type would capitalize on both the shorter length of determinate genotypes and the larger photosynthetic area and sequential fruit-setting ability of var. hardwickii. Previous unpublished data had suggested that the frequency of determinate individuals in determinate C. sativus x var. hardwickii crosses was lower than expected based on single gene recessive inheritance. Thus, another objective of the study was to further investigate this phenomenon.

A C. sativus var. hardwickii line (LJ 90430) was crossed onto four determinate C. sativus lines ('Spacemaster', NCSU M21, NCSU M27, and USDA 1909) to create four populations. Seed of the four populations was planted in 1983 at the Hancock Experimental Farm, Hancock, WI, on 1.5m centers. Individual plants in the F2 and BC1 generations to the determinate parents (BC1 P1) were classified visually into two classes, determinate (dede) and indeterminate (De-), based on vine and internode length, termination of apical growth, and leaf color (determinate genotypes generally have a darker green color). Termination of growth was determined by tagging the apex of the main stem at 10 day intervals. If the stem had not lengthened in 10 days, it was considered determinate.

Two additional populations were evaluated in 1984. In both populations the determinate C. sativus parent was NCSU M11de, which was crossed to two different indeterminate lines, LJ 90430, and a near-isogenic line, NCSU M11. Plants in the F2 and BC1P1 generations were classified by plant type, as before, except the main stems were not tagged.

In all four populations in the 1983 study, the frequency of determinate plant types in the F2 was lower than the expected 3:1 ratio (Table 1). The chi square values for goodness of fit were all significant at least at the .10 level. In contrast, segregation ratios in the BC1P1 were not significantly different from the expected 1:1 ratio, except in the 'Spacemaster' x LJ 90430 population. Some of the discrepancy in the F2 ratios could be due to misclassification. However, since fruit set was not controlled, it is likely that misclassification could have occurred in either direction (i.e. classifying a determinate individual as indeterminate or an indeterminate plant as determinate). The presence of early fruit set is known to reduce node number and deter growth in C. sativus (1,3). While other investigators have expressed difficulty in classifying determinate and indeterminate segregates (1,2), none have reported segregation ratios deviating from that expected with single gene inheritance. These investigators were not utilizing var. hardwickii germplasm, however.

Table 1. Chi square (X2) tests for plant type segregations in the F2 and BC1P1 generations of crosses between five determinate C. sativus lines and C. sativus var. hardwickii (LJ 90430), and a C. sativus x C. sativus cross (NCSU M11de x NCSU M11).

 

 

 

Generation

 

 

 

F2

 

 

 

BC1P1

 

Population

Genotype

Expected

Observed

X2

P

Expected

Observed

X2

P


1983

Spacemaster
x LJ 90430

De-

178.5

200

10.36

.001

57

69

4.28

.02-.05

 

dede

59.5

38

 

 

57

45

 

 

NCSU M21 x
x LJ 90430

De-

178.5

191

3.50

.05-.10

57.5

51

1.47

.30-.40

 

dede

59.5

47

 

 

57.5

64

 

 

NCSU M27 x
x LJ 90430

De-

180

197

6.10

.01-.02

58.5

51

1.92

.10-.20

 

dede

60

43

 

 

58.5

66

 

 

USDA 1909 x
x LJ 90430

De-

177

188

2.73

.10

54.5

63

2.65

.10-.20

 

dede

59

48

 

 

54.5

46

 

 

1984

NCSU M11de
x LJ 90430

De-

155

181

17.08

<.001

40

45

1.25

.25-.50

 

dede

52

26

 

 

40

35

 

 

NCSU M11de
x NCSU M11

De-

156

148

1.64

.20

42

37

1.19

.25-.50

 

dede

52

60

 

 

42

47

 

 


The comparison of two additional populations in 1984, revealed that the F2 segregations failed to fit a 3:1 ratio only when var. hardwickii was used as the indeterminate parent. The NCSU M11de x NCSU M11 population gave an acceptable fit to a 3:1 ratio, but the NCSU M11de x LJ 90430 population again had fewer determinate plant types than expected. However, as in 1983, both populations segregated 1:1, indeterminate:determinate, in the BC1P1

In crosses between C. sativus and var. hardwickii most of the determinate segregates in the F2 and BC1P1 resembled the respective determinate parent for lateral number. The determinate plant types that seem to be missing are those with high numbers of lateral branches. It seems likely that the plant growth regulators may be involved. More investigations are continuing.

Literature Cited

  1. Denna, D. W. 1971. Expression of determinate habit in cucumbers (Cucumis sativus L.). J. Amer. Soc. Hort. Sci. 96:277-279.
  2. Kauffman, C. S. 1973. An investigation of the inheritance of determinate habit and short internode dwarf cucumbers, Cucumis sativus L. M.S. Thesis. North Carolina State University, Raleigh, N.C.
  3. McCollum, J. P. 1934. Vegetative and reproductive responses associated with fruit development in cucumber. Cornell Agr. Exp. Sta. Memoir 163.
Home About Membership Reports Gene Lists Conferences Links Search NCSU
Department of Horticultural Science Box 7609North Carolina State UniversityRaleigh, NC 27695-7609919-515-5363
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 11 December, 2009