Cucurbit Genetics Cooperative Report 4:12-13 (article 6) 1981
James Nienhuis and R. L. Lower
University of Wisconsin, Madison, WI 53706
Reduced germination in low temperature spring soils often results in erratic stands and reduced yield potential in many agronomic and horticultural crops. For this reason, numerous breeding programs and genetic studies have been initiated with the objective of developing cultivars with improved germination, emergence and seedling vigor under adverse conditions of low soil temperatures (3,4). Low temperature tolerance in cucumbers and other vegetable crops is necessary, as uniform and rapid emergence is essential for successful mechanization of the crop. In addition, the establishment of vigorous plants under low temperature conditions would allow the extension of processing and marketing seasons (2).
The objective of this initial study was to estimate the heritability of low temperature germination, and to develop a selection procedure for population improvement.
Seeds of 210 half-sib families derived from a random mating heterogenous population of adapted cucumber lines were evaluated for percent germination at 13°C under controlled environment conditions at the University of Wisconsin Biotron. We chose a family structure (half-sibs) for evaluation of low temperature germination for several reason.
- selection among family means would be more effective with traits of low heritability.
- a family structure provides a continuous distribution of family means, as opposed to a discrete distribution among individuals.
- a family structure allows evaluation of performance at optimal as well as suboptimal temperatures. Performance of a family at optimal temperatures can be used as a check of seed viability, as well as a method to adjust family performance at suboptimal temperatures for non-genetic effects such as poorly filled or damaged seed.
Two replicated of 20 seeds from each family were placed on moist filter paper in petri dishes and evaluated for percent germination at both 13 and 25°C. Germination was defined as radicle emergence of 5 mm or longer. Narrow sense heritability among half-sib family means for germination at 13°C was estimated as 0.17 ± 0.06 (Table 1).
A recurrent selection procedure adapted from Lonnquist’s (2) modified ear-to-row selection was also initiated. The first 10 germinated seeds from each of 20 selected families (selection intensity 10%) were transplanted to the greenhouse and grown to maturity. Individuals within each family were random mated by using four randomly selected staminate flowers to pollinated each pistillate flower. This provided approximately 150 new families for evaluation in the next cycle of selection. Using this method, two cycles of recurrent selection can be completed per year. Seed from the first three cycles of recurrent selection are currently being increased under uniform environmental conditions to minimize the confounding effects of processing and storage time on progress from selection. We hope to evaluate progress from selection, as well as look at correlated responses to selection, in the fall of 1981.
Table 1. Analysis of variance for percent germination of cucumber at 13°C 10 days after seeding (arcsin transformed data).
Source |
df |
Mean squares |
Expected mean squares |
Abbreviation |
| Replication | 1 | – | – | – |
| Family | 209 | 0.0187 | s2e + 2s2f | m1 |
| Error | 209 | 0.0155 | s2e | m2 |
s2f = 1/4 s2A = (m1 – m2)/2
Literature Cited
- Lonnquist, J. H. 1964. A modification of the ear-to-row procedure for the improvement of corn populations. Crop Sci. 4:227-228.
- Lower, R. L. 1974. Measurement and selections for cold tolerance in cucumber. Pickle Pak Science IV: 8-11.
- McConnell, R. L. and C. O. Gardner. 1979. Selection for cold temperature germination in two corn population. Crop. Sci. 19: 765-768.
- Pesev, N. V. 1970. Genetic factors affecting maize tolerance to low temperature emergence and germination. Theor. Appl. Genetics 40:351-356.