Genetic Variation for Low-Temperature Germination Ability in Cucumber

Cucurbit Genetics Cooperative Report 5:16-17 (article 8) 1982

Todd C. Wehner
North Carolina State University, Raleigh, NC 27650

Low-temperature germination ability in cucumber varieties may be useful in establishing earlier and more uniform stands for spring plantings. Previous research showed that there were differences in germination speed at temperature below 17°C (1). Also % germination at 13°C had a narrow-sense heritability of 0.17 (2). The objective of this study was to identify lines with superior low-temperature germination ability, and to measure the heritability of that trait.

Cucumber lines were tested for germination speed at 15°C and 20°C in a randomized complete block design with 2 replications and 203 lines (19 cultivars, 8 breeding lines, and 176 plant introduction lines). The treatment unit was a 60 mm diameter petri plate. Each plate had 20 seeds placed on 2 layers of filter paper to which 1.5 ml of distilled water was added. The test was run for 30 days, and the number of seeds germinating each day was counted. Seeds were considered germinated when the radicle reached 6 mm in length. Average days to germination and percent germination were calculated for each treatment unit. All lines had at least 70% germination at 20°C.

Heritability of low-temperature germination was measured using parent-progeny regression. Crosses were made at random among 68 lines from the screening study, and the F1 tested as described above. Progeny means were regressed on maternal and paternal parent performance, and the narrow-sense heritability estimated as twice the regression coefficient.

The fastest 15 lines to germinate at 15°C included 7 plant introduction lines from Turkey, and 5 cultivars (Table 1). The slowest 15 lines to germinate at 15°C (excluding the 16 that did not germinate at all) were plant introduction lines, and included one Cucumis sativus var. hardwickii accession (PI 215589).

Table 1. The fastest and slowest 15 lines to germinate at 15°C (excluding 16 lines that failed to germinate).

Rank	Cultivar or Line	Seed Source	Germination at 15°C		Germination at 20°C
			Days	Percent	Days	Percent
1	PI 109484	Turkey	3.5	98	2.0	100
2	PI 222985	Iran	3.6	100	2.0	100
3	PI 174166	Turkey	3.8	90	2.0	100
4	Green Star	Harris Seed	3.9	100	2.0	90
5	PI 169392	Turkey	4.0	93	2.0	100
6	PI 222860	Korea	4.0	73	2.0	90
7	Dasher	PetoSeed	4.1	98	2.0	100
8	PI 174173	Turkey	4.1	80	2.0	100
9	Greenpak	Harris Seed	4.2	90	2.2	90
10	PI 293923	South Carolina	4.2	80	2.0	100
11	PI 164950	Turkey	4.2	50	2.2	100
12	Ashley	PetoSeed	4.3	100	2.0	100
13	PI 338236	Turkey	4.3	83	2.0	100
14	SMR 58	Petoseed	4.4	95	2.1	100
15	PI 169397	Turkey	4.5	100	2.0	100
173	PI 390252	Japan	9.0	50	2.0	100
174	PI 321009	Taiwan	9.0	43	2.0	100
175	PI 385967	Kenya	9.2	73	2.1	100
176	PI 215589	India	9.6	15	2.9	90
177	PI 401732	Puerto Rico	9.7	18	2.0	100
178	PI 390254	Japan	9.7	78	2.1	100
179	PI 390240	Japan	9.9	63	2.0	100
180	PI 306785	Canada	10.6	38	2.2	100
181	PI 206952	Israel	11.5	5	3.0	70
182	PI 357838	Turkey	11.5	3	2.0	100
183	PI 206952	Yugoslavia	11.5	23	6.1	70
184	PI 390253	Japan	13.1	58	2.0	100
185	PI 321010	Taiwan	13.5	3	4.0	90
186	PI 344435	Iran	13.6	48	2.2	100
187	PI 176953	Turkey	17.3	33	2.5	100
	LSD (5%)		3.6	45
	CV (%)		21	47

Parent-progeny correlation coefficients indicate that there is no material effect for a low-temperature germination ability (Table 2). If anything, there is a slight paternal effect, since the correlation is slightly higher between progeny and paternal parent. Narrow-sense heritability would be approximated as twice the regression of offspring on parent if the genotypes were not inbred. However, since many of the parents were inbred, heritability is closer to b than to 2b (in the range of .15 to .20). Thus, the heritability estimated by Nienhuis and Lower (2) is fairly close to the one estimated here. The low heritability may be due in part to the small standard deviation in the parents as compared to their progeny (s = 1.7 and 10.9 days, respectively).

Table 2. Parent-progeny correlation and regression estimates for days to germination at 15°C.

Parent	r	b mean s	2b
Maternal	0.16	0.14 mean 0.11	0.28
Paternal	0.18	0.15 mean 0.10	0.30

It appears that sufficient genetic variability exists for low-temperature germination ability that progress could be made by selection. The low heritability for the trait indicates that selection should be based on families rather than on individuals.

Literature Cited

1. Lower, R. L. 1974. Measurement and selection for cold tolerance in cucumber. Pickle Pak Sci. 4:8-11.
2. Nienhuis, J. and R. L. Lower1981. An estimate of the heritability of low temperature and seed germination in cucumber. Cucurbit Genet. Coop. Rpt. 4:12-13.