Medium-term in vitro conservation of virus-free parthenocarpic tomato plants

Infection of field-maintained parthenocarpic Solanum lycopersicum L. (tomato) plants with Tomato yellow leaf curl virus provided the motivation to preserve the germplasm by in vitro methods. In this study, a method for medium-term in vitro conservation of parthenocarpic tomato plants was established. As a preliminary study, the non-parthenocarpic tomato ‘Momotaro’ was used to obtain a number of uniform explants for vegetative propagation under aseptic conditions at 23°C. The modification of sucrose or mannitol concentrations in the medium alone was insufficient for the slow-growth storage of shoot cultures. In contrast, temperature had a considerable effect on the time of conservation. ‘Momotaro’ shoot cultures were pre-cultured with Murashige and Skoog (MS) medium supplemented with 2% (w/v) sucrose at 23°C for 6 d for rooting and were then stored at 10°C for further conservation. When maintained at 10°C, only 27% of the shoot cultures needed subculture even after 3 mo, whereas 100% of plants needed subculturing after approximately 2 wk., when conserved at 23°C. When the same method was used with parthenocarpic tomatoes, plants were successfully conserved at 10°C without subculture for approximately 9 mo. Moreover, field performance and genetic stability of the stored tomato plants were assessed. This newly developed method allows for easy and efficient medium-term in vitro conservation to maintain virus-free parthenocarpic tomato plants.