Some Relationships of Seed Production with Parthenocarpy and Relative Humidity in the Cucumber

Cucurbit Genetics Cooperative Report 15:11-12 (article 5) 1992

Nick E. Fanourakis and Eva E. Tzifaki
Technological Educational Institute, Heraklion Crete 71500 Greece, Institute of Viticulture Vegetable Crops and Floriculture, Hereklion, Crete, 71110 Greece

An important advantage of the cucumber plant that makes it suitable for breeding and genetic studies is its ability to produce many seeds in each pollinated fruit. A mature, hand-pollinated fruit containing more than 150 seeds is not rare. However, with parthenocarpic plants the situation is different. We have observed that the strong parthenocarpic Dutch type slicers produce generally fewer seeds per pollinated fruit than the non-parthenocarpic. Since commercial seeds of parthenocarpic cultivars are produced by hand pollination, seed cost is dependent on the number of seeds produced per pollination. The present investigation was initiated to investigate the factors affecting seed yield of parthenocarpic cucumbers in hopes of reducing seed cost.

Methods. Self- and cross-pollinations in various combinations were made among 6 inbred lines from our cucumber breeding program. Five of them were the strongly parthenocarpic, gynoecious lines 986, 987, 989 and 990. The sixth was the non-parthenocarpic, monoecious line 991 (Table 1). We counted seeds per fruit after seed extraction.

The number of seeds per fruit under two different levels of relative humidity (RH) was also investigated with several cultivars (Table 2). Two greenhouse chambers were used, one with normal (uncontrolled) RH and the other with controlled RH. Relative humidity in the uncontrolled chamber ranged from 60 to 100%. Our objective was to increase the minimum RH level to 75% in the controlled room during pollination.

Results. A wide range in the number of seeds per fruit was observed among and within crosses of the first experiment. the number of seeds varied, depending on the female parent (Table 1). Also cross-pollinations of the lines (when used as female parents) produced generally more seeds than self-pollinations. The number of seeds was dramatically decreased in the parthenocarpic fruits (mean of 51) compared to that of the non-parthenocarpic (mean of 243).

In the second experiment, the number of seeds of the parthenocarpic fruits was again much smaller compared with the non-parthenocarpic fruits in both levels of RH (Table 2). In most cases, the number of seeds per fruit was higher at high RH. However, 4 entries produced fewer seeds per fruit at high RH. Similarly, cross-pollinations of the lines did not always produce more seeds per fruit than self-pollinations.

Strongly parthenocarpic cucumber plants produced much fewer seeds than the non-parthenocarpic. However, wide variation was observed within lines. Cross-pollination of the parthenocarpic flowers did not always provide more seeds than self-pollination. The increase of RH during pollination could affect positively the number of seeds per fruit. However, other factors that influence seed production should be investigated.

Table 1. Seed number per fruit for cross- and self-pollinations of 6 cucumber lines (986 through 991).

	986		987		988		989		990		991
Statistic	Cross	Self	Cross	Self	Cross	Self	Cross	Self	Cross	Self	Cross	Self
Mean	46	21	47	47	25	21	95	23	80	35	259	226
Low	0	0	0	14	1	0	18	0	0	0	133	81
High	122	44	117	93	56	51	161	45	161	98	380	306

Table 2. Seed number of lines cross- and self-pollinated under normal (uncontrolled) and high (controlled) relative humidity.

		Controlled RH		Uncontrolled RH
Lines	Type	Mean	Range	Mean	Range
1092 parth	Selfed	20	0-74	55	13-119
1092 parth	Crossed	30	0-87	31	0-70
1098 parth	Selfed	17	0-92	5	0-24
1098 parth	Crossed	17	0-40	40	3-125
1099 parth	Selfed	55	0-201	48	0-192
1099 parth	Crossed	61	0-195	46	0-197
1100 non-parth	Selfed	150	150	147	57-150
1100 non-parth	Crossed	139	25-150	127	2-150
1094 parth	Selfed	14	0-50	0	–
1096 parth	Selfed	68	0-150	45	0-150
1113 parth	Selfed	31	0-64	14	0-72
1114 parth	Selfed	67	0-150	37	0-150
1115 parth	Selfed	75	0-150	29	0-100
1116 parth	Selfed	83	1-150	117	40-150
1117 parth	Selfed	80	1-150	65	1-150
1118 parth	Selfed	38	1-150	133	15-150
1119 parth	Selfed	129	1-150	105	6-150

Literature Cited

1. George, R.A. 1984. Vegetable seed production. Longman, London and New York.
2. Milotay, P. and S.A. Hodosy. 1991/ Evaluation of seed yield of pickling and slicing cucumbers in the field, affected by year and plant density. Cucurbit Genet. Coop. Rpt. 14:12-14.
3. Wehner, T.C. and R.R. Horton. 1988. Number of seeds per mature fruit for different types of cucumber. Cucurbit Genet. Coop. Rpt. 11:15-16.