Independence of fruit length and 10 other characters in cucumber

Cucurbit Genetics Cooperative Report 16:18-21 (article 7) 1993

Nick E. Fanourakis
Technical Educational Institute, Heraklion Crete 71500, Greece

Fruit length of cucumber exhibits great variability. Although the inheritance of fruit length has been investigated, data are not comparable because of the varying germplasm sources used and the collection and analysis measure applied (2, 3, 4, 5). Limited agreement exists regarding the inheritance of fruit length, however most researchers agree that it is a quantitative character. The quantitative nature of the inheritance of fruit length and its association with the fruit neck has been studied. (1). We report here the linkage relations of fruit length with 10 other qualitative characters of cucumber.

The long fruited line 791 from our cucumber breeding program was crossed with the non-necked American variety SMR-18 and F₂ and BC progeny were produced. Parents, F₁, F₂, BCP₁ and BCP₂ progeny were evaluated for fruit length and the following characters: bitterness (bi), powdery mildew resistance (pm), female sex expression (F), spine size (ss), warted fruit (Tu), uniform color of immature fruit (u), mature fruit color (R), glossy fruit (D), structure of epidermis (pe), and spine color (B). Evaluation and classification was made as previously described (1).

The sumbols “+” and “-” were uised to denote contrasting phenotypic classes for the segregating characters. Thus “+” stands for bitterness, femaleness, rough spines, warted fruit, nonuniform color of immature fruit, red color of mature fruit, dull fruit epidermis, palisade epidermal structure, and black spines. The “-” stands for nonbitterness, monoecious flowers, fine spines, nonwarted fruit, uniform color of immature fruit, cream color of mature fruit, glossy epidermis, flat epidermal structure, and white spines respectively. For powdery mildew “R” designates resistance, “I” intermediate resistance and “S” susceptibility.

The continuous variation of fruit length allowed for separation of F₂ and BC generations in classes differing by 8 cm. Plants were classified for other characteristics within each class of fruit length. Observed ratios within each class were compared with the total ratio of the characteristic over the classes by X² analysis. Thus the deviation of the partial ratios from the total ratio of the characteristic indicates linkage associations of any characteristic with the fruit length.

Partial phenotypic segregations and X² analysis for each particular character are generally indicated in Tables 1 and 2. Observed ratios within each class of fruit length do not indicate significant deviations from the total phenotypic character ratios. Significant deviations were, however, found in one F₂ class for female sex expression, and in some classes of the BC₁P₂ generation for spine size, warted fruit, uniform color of immature fruit, dull fruit epidermis, and structure of epidermis. The rest of the partial BC ratios for these characters follow the expected segregation. Moreover, the respective partial ratios in the F₂ generation segregate according to the expectation. Thus, it is hard to accept the observed deviation as indicative of any linkage relationships. Therefore, we propose that the segregation of the fruit length and the characteristics evaluated is independent.

Table 1. Phenotypic F₂ segregation and X² values of the 10 characters within each class of fruit length of cucumber.

Trait		Total ratio	Fruit length (cm)
			12-19, 99		20-27, 99		>28.00
			Ratio	X²	Ratio	X²	Ratio	X²
bi	+:	151	12	0.10	94	1.64	47	3.34
	-:	49	3		37		7
	R:	14	0	1.54	11	0.49	3	1.85
pm	I:	22	1		13		9
	S:	164	14		108		42
F	+:	81	9	2.36	43	3.20	29	3.91
	-:	119	6		88		25
SS	+:	157	12	0.02	95	2.33	40	1.09
	-:	43	3		35		15
Tu	+:	157	12	0.02	106	0.43	39	1.88
	-:	43	3		24		16
u	+:	157	12	0.02	106	0.43	39	1.88
	-:	43	3		24		16
R	+:	156	13	0.59	102	0.01	41	0.51
	–	44	2		28		14
D	+:	157	11	0.24	106	0.43	40	1.09
	-:	43	4		24		15
pe	+:	156	12	0.02	106	0.43	38	2.89
	-:	44	3		24		17
B	+:	155	13	0.59	101	0.06	41	0.51
	–	45	2		29		14

* Significant difference at 0.05 level.

Table 2. Segregation and X² values of the BCX₁P₂ generation for the 10 characters of cucumber within each class of fruit length.

Trait		Total ratio	Fruit length (cm)
			0-27.99		28-35.99		>36.00
			Ratio	X²	Ratio	X²	Ratio	X²
bi	+:	81	4	0.25	60	0.02	17	0.35
	-:	88	6		67		15
pm	R:	33	2	0.28	27	0.80	4	2.40
	I:	46	4		30		12
	S:	97	7		74		16
F	+:	125	7	1.86	94	0.03	24	0.24
	-:	51	6		37		8
ss	+:	55	9	8.74**	43	0.15	3	7.13**
	-:	121	4		88		29
Tu	+:	72	9	4.31*	59	0.92	4	10.68**
	-:	104	4		72		28
u	+	73	8	2.16	61	1.40	4	11.06**
	–	103	5		70		28
R	+:	92	7	0.01	69	0.01	16	0.03
	-:	81	6		60		15
D	+:	74	9	3.93*	61	1.14	4	11.45**
	-:	102	4		70		28
pe	+:	72	9	4.15*	59	1.01	4	11.00**
	-:	102	4		70		28
B	+:	92	7	0.01	69	0.01	16	0.07
	-:	84	6		62		16

*, **: significant differences at 0.05 and 0.01 levels, respectively.

Literature Cited

1. Fanourakis N.E. and E.E. Tzifaki. 19193. Correlated inheritance of fruit neck with fruit length and linkage relations with 10 other characteristics of cucumber. Euphytica (in press).
2. Imam, M.K., M.A. Abobakr and H.M. Yacoub. 1977. Inheritance of some characters in cucumber, Cucumis sativus L. II. Some quantitative characters. The Libyan J. Agric.
3. Kingston, B.D. 1973. A genetic study of some fruit characteristics of the cucumber, Cucumis sativus L. Ph.D. Thesis, Texas A and M Univ., College Station.
4. Owens, K.O. 1982. Analysis of generation means and components of variance for fruit size in two cucumber populations, and genetic and breeding studies on cucumber fruit size utilizing inbred backcross lines. Ph.D. Thesis, Univ. of Wisconsin-Madison.
5. Pike, L.M. and B.D. Kingston. 1975. Inheritance of fruit length and shape in cucumber, Cucumis sativus L. HortSci. 10:318.
6. Smith, O.S., R.L. Lower, and R.H. Moll. 1978. Estimates of heritability and variance components in pickling cucumber, J, Amer. Soc. Hort. Sci. 103: 222-225.