Correlation between Leaf Size and Horticultural Characteristics in Cucumber

Cucurbit Genetics Cooperative Report 19:21-22 (article 7) 1996

H. Mizusawa, N. Hirama and S. Matsurra
Tohoku Seed Co. 1625, Himuro, Nishihara, Utsunomiya 321-32 Japan

The little-leaf character was discovered in an inbred selection in Arkansas (1) and it was determined that this characteristic was controlled by single recessive genet at locus ll (3). Little-leaf (ll ll) is an interesting character which has been observed in cucumber. There are no Japanese greenhouse cultivars with high fruiting ability and small leaves (2). Little-leaf genotypes are horticulturally interesting (especially in greenhouse cultivation) and we have decided to introduce the little-leaf character into our breeding materials. Prior to introgression of this trait, horticultural characteristics of the little-leaf genotype were investigated. It was determined that leaf size is correlated with high number of fruits under greenhouse cultivation in Japan (2). Therefore, we felt it important to clarify the genetic and/or physiologic relationships between leaf size and other horticultural characteristics; mainly fruiting ability.

Materials and Methods. ‘Sakata’ cucumber, the local pickling variety grown in northern Japan, was used as the donor of the little-leaf character. Although ‘Sakata’ is the smallest cucumber genotype in our genetic stocks, we were not sure that ‘Sakata’ contained the ll gene. ‘Sakata’ was crossed to line ‘PA-1’ and ‘NB-1’, independently, and F1 plants were self-pollinated to produce F2 progeny for segregation analyses. ‘PA-1’ is gynoecious and possesses large leaves and gynoecious ‘NB-1’ is an intermediate-size leaf genotype. Some morphological characteristics of the three parental lines and two derived F1 progeny are listed in Table 1. One hundred and forty individuals per population were tested in the greenhouse at Utsunomiya, Japan in the summer of 1995. Leaf lengths and areas of the hypocotyl, cotyledon, true leaf, petiole an internodes of the main and lateral stems were measured. Since plants were segregated for sex type the number of pistillate flowers used was artificially controlled. Pistillate nodes were removed by pinching. The main stem was terminated at the 17th node by pinching. The first three lateral branches which appeared at the first three nodes of the main stem were removed. Fourteen primary lateral branches which appeared in the 4th to 17th nodes of the main stem were removed at the second node. Secondary branches were removed as they appeared. All pistillate flowers which formed on the main stem and the second node of the primary lateral branches were removed before flowering. The number of fruits on 14 nodes of the first node of the first lateral branch were counted as a measure of fruiting potential. Since there were no insects as pollinators in this greenhouse, fruits were parthenocarpic.

Results and Discussion. In segregating populations derived from ‘PA-1’ x ‘Sakata’, the true leaf area was significantly correlated with the petiole length (0.422**), the internodes of main stem (0.463**), and lateral branches (0.397**). On the other hand, leaf area was correlated with nursery stage characteristics and fruiting potential (Table 2). In segregating populations derived from ‘NB-1’ x ‘Sakata’ true leaf area was significantly correlated with the petiole length ().603**), but not correlated with the other length and fruiting potential characteristics examined (Table 3).

These data suggested that leaf size is correlated with some length characteristics, but not correlated with fruiting potential under the Japanese greenhouse cultivation used in this experiment. Some little-leaf segregants with normal internode length and high fruiting ability were observed and selected. These segregants may be useful germplasm as a new plant type in Japanese breeding programs.

Table 1. Morphological characteristics of three parental cucumber inbreds and two derived F₁ hybrids.

Name	Hypocotyl length (cm)	Leaf area (cm2)		Petiole length (cm)	Internode length (cm)		Number of fruit
		Cotyledon	True leaf		Main stem	Lateral stem
PA-1	5.58	27.2	766.9	28.5	7.3	21.4	12.3
NB-1	4.0	19.6	548.1	25.9	7.2	8.1	10.5
Sakata	5.7	17.2	363.7	20.3	8.2	15.9	0.0
F1(PA-1 x Sakata)	6.0	29.4	711.1	25.5	9.1	17.5	2.8
(NB-1 x Sakata)	5.9	20.7	565.5	27.9	9.0	13.8	2.7

Table 2. Correlations among six morphological characteristics and number of fruit in F₂ population derived from ‘PA-1′ x Sakata’.

Characters	1)	2)	3)	4)	5)	6)	7)
1) Hypocotyl length	1
2) Leaf area (cotyledon)	.185*	1
3) Leaf area (true leaf)	.123	.194*	1
4) Petiole length	.109	.147	.422**	1
5) Internode length (main stem)	.163*	.077	.363**	.181*	1
6) Internode length (lateral stem)	.084	.157	.397**	.084	.469**	1
7) No. fruit	.162*	.229**	.222*	-.129	.300**	.293*	1

*, ** significant at 5.0, 1.0% level, respectively.

Table 3. Correlation among six morphological characteristics and number of fruit in F₂ population derived from ‘NB-1’ x ‘Sakata’.

Characters	1)	2)	3)	4)	5)	6)	7)
1) Hypocotyl length	1
2) Leaf area (cotyledon)	.124	1
3) Leaf area (true leaf)	.025	.258**	1
4) Petiole length	-.012	.205*	.603**	1
5) Internode length (main stem)	.301**	.237**	.237**	-.143	1
6) Internode length (lateral stem)	.225**	.121	.023	-.124	.421**	1
7) No. of fruit	-.098	-.084	.029	.024	.062	.117	1

*, ** significant at 5.0, 1.0% levl, respectively.

Literature Cited

1. Goode, M.J., J.L. Bowers and A. Bassi, Jr. 1980. Little-leaf, a new kind of pickling cucumber plant. Arkansas Farm. Res. 29:4.
2. Matsuura, S. and Y. Fujita. 1995. Correlation between agronomical characters of cucumber cultivars grown in Japan. J. Soc. Hort. Sci. 64:305-313.
3. Wehner, T.C., J.E. Staub and C.E. Peterson. 1987. Inheritance of little-leaf and multi-branched plant type in cucumber. Cucurbit Genet. Coop. Rpt. 10:33-34.