Identification of highly regenerative plants within sugar beet (Beta vulgaris L.) breeding lines for molecular breeding

Abstract

Development of an efficient transformation method for recalcitrant crops such as sugar beet (Beta vulgaris L.) depends on identification of germplasm with relatively high regeneration potential. Individual plants of seven sugar beet breeding lines were screened for their ability to form adventitious shoots on leaf disk callus. Disks were excised from the first pair of true leaves of 3-wk-old seedlings or from partially expanded leaves of 8-mo.-old plants and cultured on medium with 4.4 μM 6-benzylaminopurine for 10 wk. At 5 wk of culture, friable calluses and adventitious shoots began to develop. Rates of callus and shoot formation varied between breeding lines and between individual plants of the same line. Line FC607 exhibited the highest percentage (61%) of plants that regenerated shoots on explants. Among the plants with a positive shoot regeneration response, line FC607 also had the highest mean number (8.3±1.1) of shoots per explant. Individual plants within each line exhibited a wide range of percentages of explants that regenerated shoots. A similar variation was observed in the number of shoots that regenerated per explant of an individual plant. No loss of regeneration potential was observed on selected plants maintained in the greenhouse for 3 yr. Regenerated plants exhibited normal phenotypes and regeneration abilities comparable to the respective source plants. Based on our results, it is imperative to screen a large number of individual plants within sugar beet breeding lines in order to identify the high regenerators for use in molecular breeding and improvement programs.