Effect of silver nitrate on multiple shoot formation of Virginia-type peanut through shoot tip culture

A protocol for micropropagation of Virginia-type peanut plants, an ancient crop of the New World, is reported. This study was conducted to explore the effect of silver nitrate (AgNO3), alone or in combination with growth regulators, on multiple shoot formation from shoot tip culture. Incorporation of AgNO3 into the medium, without growth regulators, induced regeneration of the explants (which did not develop at all in the AgNO3-free medium), and stimulated the emergence of axillary shoots. When AgNO3 was added in combination with cytokinins and alpha-naphthaleneacetic acid (NAA), maximum average shoot number per regenerating explant was recorded (6.3) in Murashige and Skoog (MS) medium containing 33 mu M 6-benzyladenine, 5.3 mu M NAA, and 23.54 mu M AgNO3. Moreover, AgNO3 showed a positive and marked effect on both shoot elongation and the reduction of callus proliferation from the basal ends of shoot tips. Following a period of elongation, the shoots were rooted in hormone-free MS medium, showing no residual effects due to the long-term culture in AgNO3-containing media. Acclimatization was easily obtained after plantlets were transferred to pots under greenhouse conditions, with 90% survival.