Cucurbit Genetics Cooperative Report 3:10-11 (article 6) 1980
An Estimate of Heritability of Fruit Number from a Cross
Between a Pickling Cucumber Inbred (Cucumis sativus
L.) and an Inbred of C. hardwickii R.
Department of Horticulture, North Carolina State University,
Raleigh, NC 27650
R.L. Lower and J. Nienhuis
University of Wisconsin, Madison, WI
Low fruit number per plant is the major factor in reducing
yield of once-over mechanically harvested pickling cucumbers
(4). Smith et al. (6) used a North Carolina Design I
to obtain estimates of variance components associated with
several characteristics of pickling cucumber, the narrow
sense heritability based on full-sib families for fruit
number was 0.17. The reference population was random mating
and derived from 18 inbred lines obtained from several U.S.
breeding programs (5). The low heritabilities and variances
associated with fruit number per plant in existing populations
might be increased by incorporating multiple fruiting genotypes
into the germplasm pool (6). One possible source of such
multiple fruiting genotypes is Cucumis hardwickii,
an annual monoecious Cucurbit species, which is thought
to be either a feral or progenitor species of the cultivated
cucumber (Cucumis sativus L.) (1, 3). Previous studies
reported that C. hardwickii averaged 80 fruit per
plant under North Carolina conditions (3).
The purpose of this study was to estimate the heritability
of fruit number per plant in an exotic population which
incorporated germplasm from a C. hardwickii line.
Individual plants of F2 and both backcrosses from a cross
between a gynoecious inbred line 'Gy 14', and a selection
from C. hardwickii were evaluated for fruit number per plant
in Clinton, NC, in 1978. Half-sib offspring of 53 single
plant selections based on either high fruit number (>
100) and/or high fruit weight (> 6 kg) were evaluated
in a replicated trial in Hancock, WI, in 1979.
Regression of offspring on parent was significant. The
heritability of fruit number per plant on an individual
basis was estimated as twice the regression coefficient,
and was equal to 0.88 ± 0.156 (Table 1). The 95% confidence
interval of heritability ranged from 0.57 - 1.20. One of
the assumptions of parent offspring regression was that
environmental correlations between parent and offspring
was zero (2). This was met by evaluating parents and offspring
in separate environments. Additional assumptions were made:
- Regular diploid inheritance
- Hardy-Weinberg equilibrium
- Linkage equilibrium
- No epistasis
- No maternal effects
- No assortative mating, including selfing
Parent-offspring covariance is free of genotype x environment
Incorporation of C. hardwickii germplasm has resulted
in increasing the variance and heritability of fruit number,
suggesting that selection within this exotic population
should be effective in increasing yield. Genetic correlations
due to linkage or pleiotropy between high fruit number and
other less desirable horticultural traits are unknown at
Table 1. Analysis of variance and estimates of regression
coefficients for regression of offspring on parent for fruit
Dev. from regression
60.94 ± 6.38
0.44 ± 0.078
*Significant at 1% level.
- Deakin, J.R., G.W. Bohn and T.W. Whitaker. 1971. Interspecific
hybridization in Cucumis. J. Econ. Bot. 25:195-211.
- Falconer, D.E. 1960. Introduction to Quantitative
Genetics. Ronald Press, New York, NY.
- Horst, E.R. and R.L. Lower. 1978. Cucumis hardwickii:
A source of germplasm for the cucumber breeder. Cucurbit
Genetics Coop. Rpt. No. 1:5.
- Miller, C.H., and G.R. Hughes. 1969. Harvest indices
for pickling cucumbers in once-over mechanical harvested
systems. J. Amer. Soc. Hort. Sci. 94:485-487.
- Smith, O.S. 1977. Estimation of heritabilities and variance
components for several traits in a random-mating population
of pickling cucumbers. Ph.D. Thesis. North Carolina State
University, Raleigh, NC.
- Smith, O.S., R.L. Lower, and R.H. Moll. 1978. Estimates
of heritabilities and variance components in pickling
cucumber. J. Amer. Soc. Hort. Sci. 103:222-225.