Efficient and reproducible somatic embryogenesis and micro propagation in tomato via novel structures -Rhizoid Tubers

An improved and highly reproducible system for invitro regeneration via somatic embryogenesis (S.E), applicable to several varieties of tomato (cv. Riogrande , cv. Roma grande , hybrid 17905 and model cv. M82) has been developed. First, we developed a conventional indirect organogenesis for all four varieties used in this study. The cotyledons and hypocotyls of 6-day-old tomato were used as explants (1-2 cm) for callus induction (CI) on different callus induction media (CIM) T 0 – T 12 (6-Benzylaminopurine BAP, NAA Naphthalene acetic acid, ZEA Zeatin, IAA Indole-3-acetic acid, KIN Kinetin). Maximum CI response was seen on CIMT 6 (0.5 mg/L NAA, 1 mg/L BAP) and CIMT 7 (2 mg/L IAA, 2 mg/L NAA, 2 mg/L BAP, 4mg/L KIN) in a period of 2 weeks for commercial varieties cvs. Riogrande and Roma . However, cv. M82 responded after 4 weeks to a combination of treatments [CIMT 6 (0.5 mg/L NAA + 1 mg/L BAP) and CIMT 8 (2 mg/L IAA + 2 mg/L NAA + 2 mg/L BAP + 4 mg/L ZEA)] for the production of calli. The Riogrande , being the most responsive commercial variety, was selected for invitro morphogenesis via S.E. During S.E. young cotyledons and hypocotyls explants were tested on media with different ranges of pH (3 – 7) supplemented with 0.5 and 2 mg/L NAA. Resultantly, numerous rhizoids (~38) were produced from each explant at pH4 in dark conditions. Further incubation of each rhizoid under light conditions led to the formation of a novel structure - rhizoid tubers (RTBs) on MS media supplemented with 5 mg/L TDZ/BAP at pH4. We observed that only lower pH-induced rhizoids and RTBs regenerated into multiple individual shoots on media at normal pH (5.8). The RTBs led to a complete plantlets regeneration in 45 days compared to the conventional invitro morphogenesis (60 days).