The procedures reported for the successful culture of Seneca-60 tassels (MGCNL 55:116, 1981) do not support spikelet development in field corn cultivars such as Oh43. Considerable normal tassel development in Oh43 is achieved, however, with the modifications which we now report.
Tassels 1.0 to 1.5 cm long (approximately 35-45 days from seed imbibition) are explanted into 40 ml of liquid medium in 125 ml Erlenmeyer flasks. Flasks are maintained for 21 to 23 days in a growth cabinet at 28 C and an 18 hr day (3-400 ft. c.) and 6 hr night regime. The flasks are placed flat on a white reflective surface and are not shaken during the culture period. The composition of the liquid medium and other conditions were arrived at from the following observations on the effect of different levels of sucrose, plant growth regulators, casein hydrolysate and physical conditions, such as the size of explant and shaking vs. non-shaking conditions.
To characterize growth and development, the tassels were assessed after 21 days of culture by six parameters: (1) final length; (2) final fresh weight; (3) total number of spikelets per tassel; (4) number of normal spikelets per tassel; (5) glume length and (6) number of anthers per spikelet. The response to different sucrose levels is summarized in the polygon figures (Fig. 1; a to f), where the extent of the development is represented by the relative amount of shading. For all parameters measured, the tassel explants responded to the greatest extent at a sucrose level of 0.3 M. Concentrations both below and above this value supported less development. These results with sucrose were obtained with the cytokinin, kinetin at 10-7 M and casein hydrolysate at 30 mg/l.
The importance of cytokinin for development of spikelets in culture is indicated by the data summarized in Fig. 2, a-f. At kinetin levels of 10-7 M, the maximum development of all parameters measured was achieved. At concentrations both above and below this value, significantly less development took place. At the higher concentrations (10-6 and 10-5 M), spikelet abnormalities and other inhibitory effects were common. The addition of indole acetic acid and gibberellic acid was not beneficial to development, and in fact were inhibitory at low concentrations. They were therefore not included in the medium. From some preliminary data we conclude that casein hydrolysate (30 mg/l) enhances spikelet development, though the total requirements or effects of individual amino acid supplementation have yet to be studied.
In addition to these nutritional features, the success of normal growth of spikelets is related to the initial explant size. Tassels 1.0 to 1.5 cm long underwent normal differentiation producing 100-200 normal two-flowered spikelets. Younger tassel explants (0.5 cm or less) grew abnormally and frequently produced vegetative plantlets. Older tassel explants (2-3 cm) developed poorly. Shaking is no longer considered to be necessary for significant normal development of the cultured tassels.
In summary, tassels of Oh43 grow well on a liquid medium containing M&S major and minor minerals, White's vitamins and glycine, i-inositol 100 mg/l, sucrose 0.3 M, kinetin 10-7 M, casein hydrolysate (30 mg/l).
D. R. Pareddy and R. I. Greyson
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