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) T0 - T12 (6-Benzylaminopurine BAP, NAA Naphthalene acetic acid, ZEA Zeatin, IAA Indole-3-acetic acid, KIN Kinetin). Maximum CI response was seen on CIMT6 (0.5 mg/L NAA, 1 mg/L BAP) and CIMT7 (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 [CIMT6 (0.5 mg/L NAA + 1 mg/L BAP) and CIMT8 (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).