Protocol for in vitro regeneration and rapid mass multiplication of apetalous male sterile lines of marigold

The apetalous form of male sterility, controlled by a single recessive gene (msms), is widely used for F1 hybridseed production in marigold (Tagetes spp.). Maintenance of this form of male sterility through conventionalmethods is a highly labour-intensive and costly task. Hence, we have developed a viable in vitro regenerationprotocol for rapid multiplication in three apetalous male sterile lines of marigold, MS-5, MS-7, and MS-8. Theeffect of Thidiazuron (TDZ) was assessed on in vitro establishment of apetalous male sterile lines using shoottipexplants. The modified MSm medium supplemented with 1.5 mg/l TDZ and 0.2 mg/l NAA was found suitablefor culture establishment from shoot tip explants. We have also assessed the efficiency of two cytokinins,TDZ and Kinetin (KIN), for rapid multiplication of male sterile lines of marigold. The culture media, genotypesand their interactions significantly influenced the shoot proliferation of marigold. Our findings have revealedthe superiority of kinetin over TDZ in inducing quality shoots during in vitro proliferation phase. The highestproliferation of quality shoots was obtained on modified MSm medium enriched with 0.5 mg/l kinetin and 0.1mg/l NAA. Half-strength MS medium supplemented with 0.5 mg/l of IBA was found effective for the inductionof quality roots in all the tested genotypes of marigold. Among the three male sterile lines of marigold, MS-5exhibited better in vitro establishment, proliferation and rooting abilities over the MS-7 and MS-8 lines. Thedeveloped protocol can be efficiently utilized for rapid in vitro mass multiplication of apetalous male sterilelines of marigold.