Morphological and Anatomical Comparisons between Two Cucumis sativus, Botanical Varieties: hardwickii and sativus. 

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Cucurbit Genetics Cooperative Report 8:15-18 (Article 7) 1985

Schuman, D. A., J. E. Staub and B. E. Struckmeyer
U.S. Department of Agriculture, Agricultural Research Service and Department of Horticulture, University of Wisconsin, Madison, WI 53706

Cucumis sativus var. hardwickii (R.) Alef. (C. h.) can produce 50 to 76 mature fruits per plant, and thus has potential for use by plant breeders as a genetic source for increasing yields in the commercial cucumber, Cucumis sativus var. sativus L. (C. s.) (1,3). Fruit set and seed development in C. s. restricts additional fruit set (1,2). This inhibitory or competitive effect, absent in C. h., is a major limitation for yield in C. s.

If C. h. is to be utilized in a breeding program, additional information is needed regarding the physiology, morphology, and anatomy of different accessions. Since limited morphological and anatomical information is available for hardwickii this study was designed to: 1) compare morphological and anatomical aspects of C. s. and C. h. and, 2) to determine which plant characters, if any, would allow for effective discrimination between and within these two botanical varieties.

The morphology of 5 genotypes of C. s. and 5 genotypes of C. h. were evaluated in the fall 1981 and spring 1982 in a greenhouse at Madison, Wisconsin. The 5 C. s genotypes selected each represent different morphological types.

Seeds were germinated in 5 cm peat pots containing a soil mixture of 2:2:1:1, sand:soil:peatmoss:perlite (by volume) and standard fertilization (30:30:30) was applied weekly with irrigation water. Seasonal light intensities (PPFD) for September, October, and November were 701, 469, and 325 umol s-1m-2. The temperature was approximately 27°C night.

Seedlings of each entry were transplanted to 0.2m pots, arranged in a randomized complete block design with 5 replications and harvested after 60 days. Plant height was recorded twice weekly beginning six days after transplanting. Flowers were removed because developing fruits inhibit additional growth of the plant. Length, leaf area, and dry weight were recorded at 30 and 60 days after transplanting. Leaf area was measured with a leaf area meter (Type AAM-5, Hayashi Denko Company Ltd., Tokyo, Japan). An analysis of variance was performed on morphological data and Duncan’s multiple range test was used for mean separation.

At harvest (60 days) 3 C. s. genotypes (‘Marketmore 76’, ‘Calypso’, and KY37- CG) and 2 C. h. genotypes (PI 215589 and LJ 90430) exhibiting a broad range of morphological diversity were sampled for anatomical studies. Standard microtechniques (4) were used to study transverse sections of leaves, petioles, internodes, flowers, and roots. Samples from 3 to 5 replications of each entry were combined. Leaves and petioles were excised at the sixth node, internodes between the fifth and sixth node, flowers from axillary branches at the sixth and tenth nodes, and root tips from main roots were sampled at random.

The 3 morphological plant characters measured, plant height, leaf area, and dry weight, showed substantial differences within and between cultivars of sativus and collections of hardwickii. In the fall, C. h. PI 215589 was significantly taller than all cultivars of C. s. and other C. h. collections, while PI 183967 and KY37-CG were significantly shorter (Table 1). Two C. h. (PI 273648 and PI 183967) and 2 determinate cultivars of C. s. (W2747 and KY37-CG) had similar plant heights.

In the spring, ‘Raider’ was significantly taller than it was in the fall and was similar in height to the 2 tallest collections (PI 273648 and LJ 91176). The determinate C. s. cultivars, W2747 and KY37-CG, were significantly shorter than the indeterminate C. s. cultivars. In the spring, the range in plant height among the collections of C. h. was significantly less than it was in the fall. The height of LJ 91176 and PI 215589 was great in both seasons. In the fall PI-273648 was shorter than most other collections but in the spring it had the greatest plant height.

All genotypes of C. s. except KY37-CG had greater leaf area than C. h. collections in both seasons. The leaf area of ‘Calypso’, W2747, KY37-CG, LJ 91176, LJ 90420, PI 215589 was less in the spring than in the fall. The leaf area (cm2) within the C. h. collections did not differ significantly in the fall. In the spring, PI 273648 had a statistically greater leaf area than PI 215589 and LJ 90430 (Table 1).

Dry weight for hardwickii collections had a wide range in the fall and had an intermediate range in the spring compared to C. s. cultivars. ‘Marketmore 76’ and PI 183967 had the greatest and least dry weight, respectively, for both seasons (Table 1).

Leaf thickness varied among the genotypes of C. s. but remained relatively constant in C. h. collections. ‘Calypso’ and ‘Marketmore 76’ had the greatest average leaf thickness of approximately 41 um and 43 um, respectively, while KY37-CG had a thickness of 32 um. With the exception of KY37-CG all leaves were on the average (2.3 to 5.6 um) thicker in the fall than in the spring (Table 1).

The mesophyll of all 5 C. s. genotypes had 1.5 layers of palisade cells and generally 3 layers of spongy-parenchyma except KY37-CG which occasionally had 4. The mesophyll cells of ‘Marketmore 76’ and PI 215589 were compact while KY37-CG and ‘Calypso’ and LJ 90430 had a looser arrangement. The upper epidermal layer was more prominent than the lower one in all genotypes except KY37-CG, where it was flatter.

There was 9 bicollateral vascular bundles within the stems of both C. s. and C. h. genotypes. Six of the vascular bundles are differentiated at the periphery of the internode around the 3 smaller ones near the center. The vascular bundles of the C. s. cultivars, ‘Calypso’, ‘Marketmore 76’, and KY37-CG were approximately twice the size of the C. h. genotypes LJ 90430 and PI 215589. There were more xylem and phloem elements in the 3 C. s. genotypes compared to the 2 genotypes of C. h. ‘Marketmore 76’ and KY37-CG consistently had more xylem elements than other entries.

The petioles of all lines, like the internodes, had 9 vascular bundles (except LJ 90430 which had 7). In both C. s. and C. h. genotypes, the 2 adaxial vascular bundles were nearly one-fourth as large as the 7 abaxial bundles.

Dry weight was correlated with plant height, leaf area, and number of laterals. For example, the C. h. genotype LJ 91176 was tall with an intermediate leaf area and the greatest number of laterals when compared to other genotypes, which may account for its high dry weight. On the other hand, KY37-CG and W2747 had lower dry weights resulting from a determinate growth habit and fewer laterals. The average leaf area per plant of C. s. genotypes was approximately twice that of C. h. genotypes.

Anatomical observations showed variation in leaf thicknesses between the 2 botanical varieties in both seasons. The stem diameters of the 3 C. s. cultivars were approximately twice that of the 2 C. h. collections. The phloem and xylem elements in the vascular bundles of stems of C. s. genotypes exceeded that of the C. h. genotypes. The most significant difference in the petiole of LJ 90430 was the 7 vascular bundles compared to 9 in the other genotypes. The cellular structure in the roots and flowers were similar in both botanical varieties.

Table 1. Plant height, leaf area and dry weight of cucumber genotypes grown for
60 days after transplant in fall and spring.

 
Fall 1981

 
Spring 1982

 

Genotype

Botanical
varietyz

Plant
ht. (cm)

Leaf
area (cm2)

Dry
wt. (g)

Plant
ht. (cm)

Leaf
area (cm2)

Dry
wt. (g)

PI 215589

 h 245 ay 83 de 112 abc 264 ab 78 e 39 cd

LJ 91176

 h 199 b 115 de 113 abc 274 a 107 de 38 cd

Marketmore 76

 s 198 b 233 ab 116 ab 248 b 216 b 62 a

Calypso

 s 183 bc 227 b 113 abc 253 ab 195 cd 53 b

Raider

 s 175 bc 197 bc 108 bcd 282 a 220 ab 52 b

LJ 90430

 h 159 c 89 de 104 de 212 b 70 e 37 de

PI 273648

 h 127 d 118 de 98 e 310 a 200 cd 40 cd

W2747

 s 126 d 222 b 107 cd 131 e 239 a 31 ef

PI 183967

 h 70 e 66 e 88 f 212 b 112 de 30 f

KY37-CG

 s 66 e 16 cd 101 de 131 c 172 cd 36 de

zC. sativus var. sativus (s); C. sativus var. hardwickii (h).
yDuncan’s multiple range test, means with the same letter are not significantly different (P=.05).

Literature Cited

  1. Horst, E. 1977. Vegetative and reproductive behavior of Cucumis hardwickii
     R. and Cucumis sativus L. as influenced by photoperiod, temperature, and
    planting density. M.S. Thesis. North Carolina State University, Raleigh.
  2. Nienhuis, J. 1982. Response to different selection procedures for
    increased fruit yield in two pickling cucumber populations. Ph.D. Thesis,
    University of Wisconsin, Madison.
  3. Della Vecchia, P. T. 1982. Inheritance of short-day response to flowering
    and of some fruit characteristics in crosses between Cucumis sativus var.
    hardwickii (R.) Alef. and Cucumis sativus L. lines. Ph.D. Thesis.
    University of Wisconsin, Madison.
  4. Sass, J. E. 1940. Elements of Botanical Microtechnique, 1st. ed. McGraw-
    Hill, New York.