Diallel analysis of cucumber germination at optimum and suboptimal temperatures

Cucurbit Genetics Cooperative Report 16:22-26 (article 8) 1993

P. Milotay
Vegetable Crops Research Institute, 6000 Kecskemet, P.O.B. 116, Hungary

Germination of cucumber seeds under cool weather conditions is frequently erratic resulting in poor, or non-uniform emergence. cucumber seeds germinate rapidly between 20-30C, however there is a sharp reduction in germination percentage and initial seedling development below 15C (3). Although laboratory selection of a genetically broad-base cucumber population for improved germinability at suboptimal temperature resulted in better and faster emergence in the field (4), heritability for this character is low (6). To study the nature of genetic effects controlling germination under optimum and suboptimal temperature a laboratory experiment was conducted utilizing seeds produced from a set of diallel crosses.

Five F5 to F7 generation parthenocarpic pickling cucumber lines of different origin and their hybrids were used. Seeds were produced durin the spring in a plastic house. One hundred seeds (four replications of 25 seeds) of parents and crosses were placed into the folding of moistened filter papers. Each row of seeds (one replication) were placed into the cut foldings to allow for unconstrained radicle and hypocotyl growth. The filter papers were then rolled up, and placed in plastic bags, and held in incubators in a vertical position at 17 and 25C. After 4 and 7 days at 17C and 4 days at 25C percentages of radicle protrusion, radicle and hypocotyl elongations were recorded/

Statistical analysis was carried out according to the model 2, , method 1 of Griffing (2). Before the analysis percentage data were angularly transformed. Maternal effects were estimated by the method of Topham (5).

At 25C all seed lots germinated over 95% (Table 1), and the average heterosis of hybrids was 1.02. At 17C germination proceeded slower and the average performance of hybrids over the mean of the parents was 0.89 at day four and 0.92 at day seven. At seven days the poorest seed lots germinated near 50%, while the best parents and hybrids showed maximum germination. Keeping lagging lots seeds at 17C to day 12 resulted in only a slight improvement.

Radicle elongations showed relatively small, but significant differences at optimum temperature (Table 2). More marked differences were detected at 17C resulting in an average heterosis of 1.22 and 1.06 at day four and day seven respectively. Variability increased within the seed lots at suboptimal temperature also. Hypocotyl development followed radicle protrusion by 1.5 days at optimum temperature and about 3 days at suboptimal temperature (data not shown).

The Griffing analysis resulted in significant general combining ability (gca) and specific combining ability (sca) effects for all characters at both temperatures. Reciprocal effects were also significant except for germination percentage at 25C. According to the variances (Table 3), dominance and non-allelic effects were much more important than additive effects at suboptimal temperature both for germination percentage and seedling growth. The average degree of dominance for these characters refers to over-dominance. At 25C, over-dominance was found only for germination percentage and radicle elongation was conditioned by additive genetic effects.

When analyzing gca effects, line KP exhibited significantly positive values, and line 17K significantly negative values for percent germination at 17C. In case of radicle growth, lines Ac18 and KP produced significantly positive gca values at the same temperature (data not shown).

Narrow-sense heritability values obtained for percent germination were not significant at both temperature and radicle elongation gave only higher heritability at 25C (h2 = 0.62). Significant maternal effects in this study were obtained at sub-optimal temperature for percent germination (0.68) and radicle length growth (0.77). At optimum temperature only for radicle length (0.61) was significant. The nature of this effect should be studied further (1).

The parthenocarpic pickling cucumber lines involved in this study do not provide suifficient genetic base for improving germinating ability at suboptimal temperature.

Table 1. Germination of cucumber seeds at 35C after 4 days, at 17C after 7 days, and at 17C after 4 days (transformed data).

Parents	Temp/days	S750	Ac18	M72	KP	17K	Mean
S750	25/4	87.1	90.0	90.0	85.9	90.0	88.6
	17/7	85.9	82.0	70.7	47.3	52.4	67.6
	17/4	83.3	75.4	56.690.0	31.4	42.3	57.8
Ac18	25/4	90.0	90.0	82.6	87.1	90.0	89.4
	17/7	87.1	72.6	70.7	80.0	51.7	74.9
	17/4	83.3	66.5	77.1	72.6	42.4	67.1
M72	25/4	90.0	87.1	60.5	87.1	81.8	84.8
	17/7	87.1	75.6	53.8	81.3	47.9	70.5
	17/4	82.0	67.1	90.0	78.5	35.9	63.5
KP	25/4	90.0	87.1	87.1	90.0	90.0	89.4
	17/7	90.0	90.0	83.3	90,0	56.9	82.8
	17/4	90.0	85.9	90.0	80.4	35.0	74.9
17K	25/4	90.0	87.1	90.0	90.0	90.0	89.4
	17/7	83.0	84.1	66.9	86.4	90.0	78.1
	17/4	55.6	75.7	62.8	82.1	84.2	72.1
Mean	25/4	89.4	88.3	87.4	88.0	88.4	88.3
	17/7	82.6	80.9	73.5	77.0	59.8	74.8
	17/4	78.8	74.1	65.4	69.0	48.0	67.1

Critical differences at 25C after 4 days, 17C after 7 days and 4 days = 3.9, 8.8 and 10.7, respectively

Table 2. Radicle length (mm) of cucumber seedlings at 25C after 4 days, at 17C after 7 days and at 17C after 4 days.

Parents	Temp/days	S750	Ac18	M72	KP	17K	Mean
S750	25/4	93.8	103.6	100.3	90.2	93.5	96.3
	17/7	48.7	58.4	54.5	35.1	35.6	46.5
	17/4	9.1	12.4	11.4	2/9	6.3	8.4
Ac18	25/4	105.2	105.1	106.9	102.1	93.8	103.8
	17/7	81.3	49.9	56.0	64.0	38.6	54.0
	17/4	12.3	5.9	7.2	10.6	4.4	8.1
M72	25/4	99.2	105.1	93.1	99.4	80.5	95.5
	17/7	60.8	53.0	44.9	63.1	43.4	53.0
	17/4	15.1	10.2	4.1	11.5	5.8	9.3
KP	25/4	104.7	106.2	106.3	97.4	85.8	10.1
	17/7	65.2	68.6	64.8	53.2	34.1	57.2
	17/4	16.3	17.3	15.6	11.8	7.0	13.7
17K	25/4	89.6	95.6	97.5	96.9	85.3	95.0
	17/7	42.2	51.9	53.8	50.4	53.6	50.4
	17/4	11.0	11.0	12.4	10.4	12.3	11.4
Mean	25/4	98.5	103.1	100.8	87.2	91.0	98.1
	17/7	55.8	56.4	54.8	53.2	41.4	52.2
	17/4	12.9	11.4	10.1	9.4	7.2	10.2

Critical differences at 25C after 4 days, 17C after 7 days and 4 days = 3.4 5.5 and 2.6, respectively.

Table 3. Variances and genetic components of germination and seedling growth analyzed by Griffing’s method 1.

Character	Mg	Ms	Mr	Me	ó²g	ó²s	h²	a
OPTIMUM TEMPERATURE
Germination %	16.25**	10.79*	5.44 ns	4.46	0.58	3.77	0.12	1.81
Radicle length	139.70***	21.50***	36.30***	4.85	23.80	9.33	0.62	0.65
SUBOPTIMUM TEMPERATURE
Germination % day 4	236.93***	260.96***	428.47***	33.58	0.00	135.00	0.02	—
Germination % day 7	194.22***	204.21***	235.63***	24.87	2.15	106.76	0.02	6.81
Radicle length day 7	159.16***	98.12***	78.99***	6.61	6.54	54.43	0.18	2.04

*, **, *** = significant at 5, 1 and 0.1% level, respectively.

Literature Cited

1. Edwards, M.D. and R.L. Lower. 1982. The genetic regulation of several seed traits in compact (cpcp) cucumbers – Maternal vs. embryonic control. Cucurbit Genet. Coop. Rpt. 5:8-9.
2. Griffing, B. 1956. Concept of general and specific combining ability in relation to diallel crossing systems. Austr. J. Biol. Sci. 9:463-493.
3. Simon, E.W., A. Minchin, M.M. McMenamin, and J,M. Smith. 1976. The low temperature limit for seed germination. new Phytol. 77:301-311.
4. Staub, J.E., R.L. Lower and J. Nienhuis. 1988. Correlated responses to selection for low temperature germination in cucumber. HortScience 23.4:745-746.
5. Topham, P.B. 1966. Diallel analysis involving maternal and maternal-intractiuon effects. Heredity 21:665-674.
6. Wehner, T.C. 1982. Genetic variation for low-temperature germination ability in cucumber,. Cucurbit Genetic Coop. Rpt. 5:16-17.