Hormone-free medium will support callus production and subsequent shoot regeneration from whole plant leaf explants in some sugarbeet (Beta vulgaris L.) populations

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Abstract
Sugarbeet plants representing 14 of 16 germplasm sources (4 to 5 plants per source) produced callus from leaf disks on a hormone-free Murashige and Skoog based medium. Overall, 49.2% of explants from partially expanded leaves of whole plants initiated callus (53 of 74 plants tested), in an average time of 96.7 days. The time to callus was considerably longer than the 4–6 weeks observed when 1 mg/L N6-benzyladenine has been used in the medium. Shoots were regenerated on the hormone-free medium without subculture from callus of eight individual genotypes, representing 3 of the 14 populations that produced callus. Shoots produced by ‘Gartons White Knight’ and ‘L53’ appeared to be of somatic embryo origin. Rhizogenic calli were also produced by the same three populations that regenerated shoots. Significant differences among populations were found for frequency of root formation from leaf disks and time to callus. Variation among plants within a population was significant for four of the five traits examined. The results indicate the ease of hormone autonomization in sugarbeet, and should be of value in designing regeneration media for a wider range of beet germplasm.