The number of vascular bundles in 18 different cultivars of inbred, hybrid or commercial sweet corn --Cheng, WY, Cheng, PC, Walden, DB This article reports a study on the vascular bundles in a number of cultivars. In this study, inbred, hybrid lines and mutants were grown in the nurseries at the University of Western Ontario (London, ON, Canada) in the summers of 1999, 2000, and 2001. The inbred lines used in this study included Oh43, B73, W23, CM48, KYS, Mo17, and Gaspé. Hybrids were Oh43/B73, Oh43/W23, Oh43/CM48, Oh43/Gaspé, Oh43/Mo17, Oh43/KYS, CM48/Oh43, CM48/Gaspé, CM48/W23, Mo17/B73, and B73/Mo17. In addition, commercial sweet corn varieties, including: �Platinum Lady,� �Honey and Cream,� �Seneca Chief,� and �Odyssey,� were employed. In order to determine the effect of parental influence on stem development, reciprocal F1 hybrid plants where available also were employed. The specimens were harvested and fixed in methanol and/or EtOH/acetic acid (3:1), serially sectioned with a razor blade using a special jig we made. The hand sections, approximately 800 µm in thickness, were de-colored in 70% iso-propanol, dehydrated in acetone and cleared in xylene. The number of vascular bundles, cross-sectional area of the immediate (1st) internodes and second internodes (2nd) below the main ear-bearing node, and perimeter of the stem were obtained by using the counting function in ImageAcquireTM software (Williamsville, NY).

A minimum of five samples were collected from each variety at silking. The data were tabulated and a Student T-test was performed. For further analyses, the cross section of an internode was subdivided into three zones: the para-epidermal zone 1 (19% of the total area), zone 2 (56%) and zone 3 (pith) (25%). This zoning was achieved by first detecting the edge of the stem by intensity threshold, followed by edge-detection using an image processing software (Paint Shop Pro, v5.0). This procedure obtained the outline of the stem which could then linearly reduce the outline to 50% and 90%. Finally, the outline was pasted onto the original image to define the zoning (Fig. 1). Cross sectional area (in mm2) and stem perimeter (in mm), as well as the number of vascular bundles, were obtained using ImageAcquireTM. Statistical analyses were performed using Origin software (V5.0, Microcal Inc., MA).

In a systematic study of various inbreds and their F1 hybrids, a number of interesting observations were made. While the general pattern of vascular distribution is similar, the numbers of vascular bundles and cross sectional areas of the stem can be significantly different. For a given cultivar, the standard deviation of the number of bundles is well within 5-10% of the value, while cross-sectional areas show a much larger standard deviation (Fig. 2 and Table 1). These observations suggest that the vascular bundle number is largely determined genetically and may be set in the embryonic phase, while the internode cross sectional area is more influenced environmentally. In B73/Mo17, Oh43/CM48, and their reciprocal F1 hybrids, the number of vascular bundles shows no significant difference (Fig. 2-C to 2-F), suggesting that cytoplasmic factors may have little influence in the determination of vascular numbers. Depending on the parental backgrounds, the F1 hybrids show a significant "hybrid vigor" in increasing the number of vascular bundles and cross sectional area (e.g. Oh43/KYS and B73/Mo17), although the early maturing hybrids, (CM48/Gaspé and Oh43/Gaspé) have bundle counts which resemble one of the parents or are an intermediate between the parents (Fig 2-G, 2-H). However, the results may indicate the degree of genetic similarity in the inbred lines used in this study as far as the vascular development is concerned. For comparison, the data from four commercial sweet corn varieties are also shown in Fig. 2-I, 2-J. It is important to note that for proper comparison, all the samples examined were obtained at the half silk stage; the time required from planting to silking is listed in Table 1.

This article is part of a report by WYC for Siemens Westinghouse Science and Technology Competition (Semi Finalist) and Intel Science Talent Search (2001).

Figure 1. Definition of zoning used in this article. Zone 1: 19%, Zone 2: 56%, Zone 3: 25%

Figure 2. Histograms showing the number of vascular bundles (1st three bars from left) in zone 1, 2, and 3 respectively, number of total bundles (4th bar), cross sectional area of stem (5th bar) and stem perimeter (6th bar) for the two internodes below the top ear node in different cultivars.

Table 1. Comparison of the CS area (mm2), and perimeter (mm), the number of vascular bundles in zones 1, 2, 3 and total, and the number of bundles in zone 1 per mm of stem perimeter (B/mm) from two internodes of various inbreds, hybrids, and commercial sweet corn hybrids. n: sample size.
 
Cultivars
(1st, 2nd internode)
n
Days to half Silking
Cross sect. Area
(mm2)
Perimeter
(mm)
Total Bundles
Zone 1
Zone 2
Zone 3
B/mm
Oh43 1st
7
73
178.70 + 62.93
59.33 + 12.08
393.7 + 14.6
235.0 + 8.5
124.5 + 2.3
32.7 + 5.6
3.9
Oh43 2nd
5
73
182.67 + 40.46
57.07 + 5.36
447.0 + 9.6
265.0 + 9.8
145.8 + 2.5
36.2 + 2.7
4.6
Gaspé flint 1st
7
41
44.22 + 18.98
29.81 + 5.70
158.8 + 8.4
84.0 + 3.1
60.8 + 5.9
14.0 + 2.6
2.9
CM48 1st
7
64
151.50 + 37.74
54.16 + 5.64
352.0 + 7.0
222.0 + 3.3
99.2 +3.0
30.8 + 3.0
4.1
CM48 2nd
7
64
165.55 + 26.18
54.34 + 4.3
322.8 + 10.8
213.0 + 7.3
85.2 + 24.6
24.6 + 4.7
3.9
KYS 1st
4
89
347.44 + 20.27
82.30 + 3.41
460.2 + 9.4
288.5 + 7.5
130.2 + 5.1
41.5 + 2.6
3.5
KYS 2nd
5
89
431.48 + 19.37
91.88 + 1.37
552 + 6.4
354.7 + 8.3
149.7 + 2.9
47.5 + 1.0
3.8
Mo17 1st
5
83
191.62 + 15.60
59.29 + 2.03
340.6 + 7.7
224.8 + 4.
92.8 + 5.4
23.0 + 3.5
3.7
Mo17 2nd
6
83
174.14 + 17.07
55.75 + 2.41
363.8 + 9.9
206.3 + 7.3
129.5 + 5.7
28.0 + 4.4
3.7
B73 1st
7
80
179.01 + 43.55
60.31 + 8.22
326.5 + 49.6
213.5 + 29.3
89.5 + 17.7
23.4 + 5.4
3.5
B73 2nd
8
80
186.47 + 67.02
58.86 + 10.84
308.8 + 86.3
164.2 + 65.5
116.1 + 17.3
28.5 + 5.5
2.7
Mo17/B73 1st
7
74
249.08 + 51.04
70.59 + 7.47
464.7 + 25.8
304.8 + 17.6
127.4 + 10.9
36.1 + 4.4
3.9
Mo17/B73 2nd
7
74
331.02 + 75.69
78.07 + 8.31
510.4+ 21.8
316.8 + 15.2
152.4 + 8.5
41.1 + 3.6
4.0
B73/Mo17 1st
7
76
284.29 + 65.33
75.28 + 7.01
468.4 + 32.1
295.2 + 20.6
131.2 + 12.7
38.1 + 3.1
3.8
B73/Mo17 2nd
7
76
284.58 + 66.01
72.29 + 9.13
480.1 + 64.1
318.2 + 57.8
120.1 + 29.3
41.7 + 2.5
4.4
CM48/Oh43 1st
5
61
229.16 + 17.77
67.49 + 7.25
401.2 + 9.4
254.4 + 11.3
111.2 + 10.3
34.6 + 3.2
3.7
CM48/Oh43 2nd
7
61
301.72 + 30.27
77.57 + 2.91
442.5 + 14.5
272.8 + 8.5
130.1 + 8.0
39.5 + 1.9
3.5
Oh43/CM48 1st
7
63
184.89 + 44.08
60.12 + 7.25
393.2 + 23.7
254.4 + 15.0
106.7 + 10.3
32.1 + 3.2
4.2
Oh43/CM48 2nd
7
63
223.32 + 71.98
62.32 + 9.25
416.1 + 29.1
258.4 + 21.9
121.7 + 10.6
36.0 + 4.2
4.1
Oh43/Gaspé 1st
5
58
163.60 + 21.88
57.64 + 4.0
278.6 + 38.4
172.6 + 27.5
84.4 + 10.0
21.6 + 3.0
2.9
Oh43/KYS 1st
7
88
367.31 + 77.69
86.54 + 8.98
580.4 + 34.3
369.1 + 18.0
166.2 + 13.8
45.0 + 3.7
4.2
Oh43/KYS 2nd
4
88
477.98 + 99.00
92.45 + 9.37
685.0 + 44.5
421.2 + 25.5
212.5 + 18.1
51.2 + 3.2
4.5
CM48/Gaspé 1st
5
59
172.51 + 38.76
56.53 + 6.54
307.1 + 40.2
204.8 + 20.9
81.1 + 22.8
21.1 + 3.8
3.6
Platinum Lady 1st
7
72
177.63 + 36.23
60.64 + 5.45
324.7 + 33.5
214.2 + 17.8
83.0 + 14.4
27.4 + 2.9
3.5
Platinum Lady 2nd
7
72
215.59 + 32.57
63.73 + 4.87
345.7 + 23.3
212.5 + 13.4
103.5 + 9.8
29.5 + 1.7
3.3
Honey & Cream 1st
7
70
196.29 + 14.79
60.16+ 1.94
379.1 + 21.6
252.5 + 14.5
95.5 + 9.1
31.1 + 4.3
4.1
Honey & Cream 2nd
7
70
256.35 + 20.96
69.64 + 2.45
404.0 + 16.8
244.5 + 11.7
123.7 + 7.1
35.7 + 2.7
3.5
Seneca chief 1st
7
75
278.38 + 33.09
74.58 + 4.89
443.4 + 25.9
293.0 + 17.9
118.0 + 10.2
32.4 + 2.2
3.9
Seneca chief 2nd
7
75
320.68 + 32.96
76.15 + 4.88
474.5 + 16.1
298.2 + 11.4
138.1 + 10.0
38.1 + 3.7
3.8
Odyssey 1st 
7
78
218.30 + 60.94
67.92 + 8.84
425.1 + 34.1
272.5 + 17.8
119.0 + 14.5
33.5 + 4.9 
4.0
Odyssey 2nd
7
78
267.83 + 67.89
71.45 + 8.62
526.1 + 45.6
348.4 + 30.8
140.0 + 22.1
37.7 + 4.3
4.8

 
 
 

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