Cucurbit Genetics Cooperative Report 10:33-34 (article 20) 1987

Inheritance of Littleleaf and Multi-branched Plant Type in Cucumber

Todd C. Wehner

Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609

Jack E. Staub and Clinton E. Peterson

Department of Horticulture, U.S.D.A., University of Wisconsin, Madison, WI 53706

Little-leaf is a plant type discovered in an inbred selection in Arkansas. Goode et al. (1) reported that the F₁ of several crosses was normal, and the F₂ (resulting from self-pollination of the F₁) segregated in a ratio which suggested a 3:1. It has leaves, stems and flowers smaller than normal, and multi-branched vines. The multi-branched habit is similar to the Cucumis sativus var. hardwickii line, LJ 90430. The Goode et al. little-leaf line ('Little John') holds up better than normal leaf lines such as 'Calypso' under the rough treatment they receive during multiple harvest. It also seems to grow better than the normal cultivars under dry or windy conditions. That is at least partly due to the small, tough leaves on the plant.

Breeders are using the new plant type to incorporate the small leaf habit and/or the multi-branched habit into commercially acceptable lines. Although it appears to be a single-gene mutant, and the symbol ll has been used as a symbol to represent the trait (2), no inheritance data have been published. The objective of this study was to determine the inheritance of the two most important traits of 'Littleleaf', small leaves, and multi-branched plant habit.

Methods. 'Little John' was crossed as the paternal parent to 'Wisconsin 2757' and the F₁ were self-pollinated and backcrossed to each parent to form 6 generations for testing: Pa (W2757), Pb (Little John), F₁, F₂ BC₁Pa, and BC₁Pb. The 6 generations were tested in the field at Hancock, Wisconsin in the summer, 1986 using randomized, replicated and coded treatments to prevent bias during evaluation. Data were checked for fit to the expected 3:1 ratio using a Chi-square analysis. The multi-branched data were coded such that 0 to 2 = few, and 3 to 5 = many branches. Branching was also evaluated using generation variances where phenotypic = F₂ variance, and additive = 2(F₂)- (BC₁Pa)-(BC₁Pb) variances. Narrow-sense heritability was calculated as additive/phenotypic variance.

Results. Multi-branched habit did not follow any single-gene inheritance pattern we could determine. It must, therefore, be considered a quantitative trait. Unfortunately, heritability of multi-branch was approximately 0 using generation variances. In the cross of two other inbreds (data not shown) the heritability was 0.61, but the data from several crosses we have studied is extremely variable.

On the other hand, the littleleaf trait of 'Little John' is controlled by a single recessive gene (Table 1). Some of the plants were misclassified (see, for example, the F₁ data) due to environmental variability for leaf size. Thus, littleleaf can be considered a good marker, already named ll, where 'Little John' carries the recessive mutant allele, and W2757 (as well as most other cucumber lines) carries the dominant, wild-type allele.

Table 1. Inheritance of littleleaf trait (ll) in the cross of 'WI 2757' (Pa) x 'Little John' (Pb).

Literature Cited

1. Goode, M.J., J.L. Bowers and A. Bassi, Jr. 1980. Little-leaf, a new kind of pickling cucumber plant. Arkansas Farm Res. 29:4.
2. Zijlstra, S. and A.P.M. den Nijs. 1986. Further results of linkage studies in Cucumis sativus L. Cucurbit Genet. Coop. Rpt. 9:55.