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

Abstract

The apetalous form of male sterility, controlled by a single recessive gene (msms), is widely used for F1 hybrid seed production in marigold (Tagetes spp.). Maintenance of this form of male sterility through conventional methods is highly labour-intensive and costly. Hence, we have developed a viable in vitro regeneration protocol for rapid multiplication in three apetalous male sterile lines of marigold, MS-5, MS-7, and MS-8. The effect of Thidiazuron (TDZ) was assessed on in vitro establishment of apetalous male sterile lines using shoot-tip explants. The modified MSm medium supplemented with 1.5 mg/l TDZ and 0.2 mg/l NAA was suitable for 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, genotypes and their interactions significantly influenced the shoot proliferation of marigolds. Our findings have revealed the superiority of kinetin over TDZ in inducing quality shoots during in vitro proliferation phase. The highest proliferation of quality shoots was obtained on a modified MSm medium enriched with 0.5 mg/l kinetin and 0.1 mg/l NAA. Half-strength MS medium supplemented with 0.5 mg/l of IBA was found effective for the induction of quality roots in all the tested genotypes of marigold. Among the three male sterile lines of marigold, MS-5 exhibited better in vitro establishment, proliferation and rooting abilities over the MS-7 and MS-8 lines. Therefore, the developed protocol can be efficiently utilized for rapid in vitro mass multiplication of apetalous male sterile lines of marigold.