In this report I describe the growth behavior of callus of different origins. Sources of the callus were the inbred A 188 and two stocks, one homozygous for sh wx gl15 v and the other for yg, kindly provided by the Genetics Co-op. They will be referred to as S 1106 and S 1104 respectively. They have been chosen because of their tendency to form callus from the scutellum of mature seeds germinated on agar.
Callus induction from mature seeds has been obtained in detached embryos cultured on the Murashige and Skoog medium (1962) modified by Green (1975) with 4 mg/l 2-4D at 27 C ± 1, under continuous light. Under these conditions seedlings are produced with an extremely abnormal morphology, particularly in the mesocotyl and in the first node region where the callus develops. Callus is also obtained from roots, particularly those in contact with the medium. After 30 days callus is excised and transferred to a medium with 2 mg/l 2-4D. Subcultures are performed every four weeks.
The growth pattern of the three callus lines is shown in Figure 1, where each determination is the average of at least five replications. The lines differ in their growth, with S 1104 showing the fastest growth.
The amount of growth seems to depend on the initial weight of the explant as the data below indicate (S 1104 data only).
The three lines show also morphological differences. Callus of S 1104 is friable, yellow with green spots, and shows areas with anthocyanin. No pigment is observed in the other two lines, which appear more compact. The three lines have been subcultured for 11 months.
Callus also has been obtained from immature embryos following the procedures outlined by C. E. Green and R. L. Phillips (1975). When 16-18 day-old embryos are excised and incubated on MS modified medium with 2 mg/l 2-4D, the scutellum gives rise to a yellow or pale green callus; subcultures have been propagated on the same medium. When callus is transferred to a medium with 0.25 mg/l 2-4D, roots start to differentiate. If these cultures are then transferred to a medium without hormone, roots are still formed, but in addition, shoot-like structures are also observed. These structures do not differentiate into plantlets. In the S 1106 line, however, three explants developed plantlets (3-4 from each piece) that were not further analyzed.
M. L. Racchi
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