In vitro selection of calli of Citrus jambhiri Lush. for tolerance to culture filtrate of Phytophthora parasitica and their regeneration.

The present study deals with the selection of Phytophthora tolerant lines of Citrus jambhiri and their regeneration. Cotyledon derived calli were cultured on selective MS medium supplemented with 5-100 % of culture filtrate (CF), to estimate the critical concentration of the selective agent. The survived calli under stress were subcultured for mass propagation for 20 days on callus multiplication medium (2,4-D 2 mg/L + BA 0.75 mg/L) without culture filtrate. After multiplication, these calli were further exposed to other cycles of selection, which contained the same and the 3 steps higher concentrations of the selective agent (CF) and this procedure was repeated several times until the selection regime completed. The selected tolerant calli were transferred to regeneration medium (MS medium supplemented with 3 mg/L of BA and same concentration of culture filtrate on which the calli were selected). Regenerated shoots were transferred to rooting medium (½ strength MS medium supplemented with 0.5 mg/L of NAA). Under in vivo conditions about 81 % of the selected regenerates exhibited resistance to Phytophthora parasitica, whereas none of the control plants showed resistance.