correlated with the multiple-harvest test to be substituted com- pletely. Also, the rapid tests do not necessarily provide adequate measure of earliness, quality, and stress resistance. The small- plot, once-over harvest test provides an excellent method for evaluation of families from recurrent selection, and for devel- opment of lines for use as hybrid cultivars. Literature Cited 1. Christidis, B.G. 1931. The importance of the shape of plots in field experimentation. J. Agr. Sci. 2:14-37. 2. Gardner, C.O. 1961. An evaluation of effects of mass selection and seed irradiation with thermal neutrons on yield of corn. Crop Sci. 1:241-245. 3. Hallauer, A.R. and M.B. Miranda, Fo. 1981. Quantitative ge- netics in maize breeding. The Iowa State Univ. Press, Ames. 4. Hatheway, W.H. and E.J. Williams. 1958. Efficient estimation of the relationship between plot size and the variability of crop yields. Biometrics 14:207-222. 5. Koch, E.J. and J.A. Rigney. 1951. A method of estimating op- timum plot size from experimental data. Agron. J. 43:17-21. 6 . Lonnquist, J.H. 1964. A modification of the ear-to-row procedure for the improvement of maize populations. Crop Sci. 4:227-228. 7. Miller, C.H. and G.R. Hughes. 1969. Harvest indices for pickling cucumbers in once-over harvest systems. J. Amer. Soc. Hort. Sci. 94(5):485-487. 8. Pearce, S.C. 1976. An examination of Fairfield Smith's law of environmental variation. J. Agr. Sci. 87:21-24. 9. Smith, H.F. 1938. An empirical law describing heterogeneity in the yield of agricultural crops. J. Agr. Sci. 28:1-23. 10. Smith, O.S. and R.L. Lower. 1978. Field plot techniques for selecting increased once-over harvest yields in pickling cucum- bers. J. Amer. Soc. Hort. Sci. 103( 1 ):92-94. 11. 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(2):222-225. 12. Sprague, G.F. 1952. Early testing and recurrent selection. In: John W. Gowen(ed.). Heterosis. Iowa State College Press, Ames. J. Amer. Soc. Hort. Sci. 109(5):664-667. 1984. Estimates of Heritabilities and Variance Components for Low-temperature Germination Ability in Cucumber Todd C. Wehner 1 Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609 Additional index words. Cucumis sativus, cold tolerance, vegetable breeding, North Carolina Design I, quantitative genetics Abstract. Variance components for low-temperature germination ability in cucumber (Cucumus sativus) were esti- mated for 3 germination variables (actual days to germination, days to 50% germination, and percentage of germi- nation) at 17°C using a North Carolina Design I analysis. The estimates were made using the North Carolina Medium Base Pickle (NCMBP) population, which was developed by intercrossing adapted pickling cucumber cultivars with diverse lines for 3 cycles without selection. Estimates of additive and dominance variance for the percentage of germination and days to 50% germination were equal, but additive variance was predominant for actual days to germination. Heritabilities based on half-sib families tested in 2 replications ranged from 0.44 to 0.61 for the 3 germination variables. There were large significant genetic correlations among the 3 germination variables, ranging from 0.61 to 1.03 in absolute value. Selection for either the percentage of germination or for actual days to germination at 17° should result in significant progress in improving low-temperature germination ability of cucumbers in the NCMBP population. Low-temperature germination ability has been studied in veg- etable crops for several decades using seed sprouting response in cold chambers, and has been found to be both heritable and a useful predictor of field emergence under adverse conditions. Narrow sense heritability for low-temperature germination abil- ity in 2 different tomato ( Lycopersicon esculentum Mill.) pop- ulations was 0.25 (5) and 0.66 (13), respectively. Cold tests are valuable tests of seed vigor, but have been used with varying degrees of success. Cold test results were not cor- related with field emergence in tomato ( 1 ), but were positively Received for publication 11 Oct. 1983. Paper No. 8908 of the Journal Series of the N.C. Agr. Res. Ser., Raleigh, NC. The author gratefully acknowledges the technical assistance of R.R. Horton, Jr. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. ‘Assistant Professor. correlated for maize (Zea mays L.) (12). Cold tests for germi- nation of carrot ( Daucus carota L.) seeds had a high correlation with field emergence and provided better prediction of field emergence than the standard germination tests run at optimum temperature conditions (7). In cotton (Gossypium hirsutum L.), high (25°C) and low (15°) temperature germination results were not correlated (2). The best tomato lines germinating at cold temperatures were not necessarily the best ones for low tem- perature seedling growth, plant growth, or fruit setting (8). The mechanism of cold tolerance has been studied. For example, failure of low-temperature germination in cucumber (Cucumis sativus L.) was not due to damage from imbibing cold water, to loss of membrane integrity, or to failure of mitosis, but was most likely due to denaturing of proteins (16). Incorporation of low-temperature germination ability into cuc- umber cultivars should be useful for establishing early uniform stands in spring plantings. If combined with cold tolerance at the seedling stage, it also may be possible to extend the growing 664 J. Amer. Soc. Hort. Sci. 109(5):664-667. 1984.