Microtuberization efficiency of three potato (Solanum tuberosum L.) cultivars under osmotic stress in vitro

Potato (Solanum tuberosum L.) is one of the most important crops worldwide. It is vegetatively propagated using pieces or whole potato tubers, but a virus infection causes crop reduction to almost a half or even one third, which varies from place to place and from season to another. Micropropagation is the practice of rapidly multiplying stock plant material to produce many progeny plants, using modern plant tissue culture methods. Microtuberization in potato needs the right interaction between several factors such as cyto, sucrose and osmotic stress. The purpose of present study was to investigate microtuberization efficiency of three potato cultivars under osmotic stress and in vitro conditions.

This experiment was carried out based on completely randomized design (CRD) in three replications. Potato seeds of three cultivars (Agria, Savalan and HPS-II/67) were cultured on Murashige and Skoog (MS) medium. After proliferation, plantlets were transferred to the media containing nine treatments with polyethylene glycol hydrogel (PEG) at four levels (0.003, 0.006, 0.009, 0.012 M), sorbitol at four levels (0.1, 0.2, 0.3, and 0.4 M). For this purpose, potato quality, microtuberization percentage, proline concentration, chlorophyll content, and Catalase (CAT) and superoxide dismutase (SOD) activities were measured.

The results showed that plantlets grown under non-stressed conditions (control) possessed higher rates of leaf number, new shoot length and proliferation index compared to the under stressed conditions. Agria cultivar presented better growth characteristics under stressed conditions compared to other experimental cultivars. The highest potato destruction was observed at 0.012 M PEG in Savalan cultivar followed by 0.4 M sorbitol in all cultivars. Microtuberization percentage increased in all three cultivars by stress conditions, in which it increased with progressing in stress levels. The greatest percentage of microtuberization was obtained from Agria cultivar at 0.003 M PEG. Compared to the control, proline concentration, and also CAT and SOD activities increased under stress conditions. Moreover, total chlorophyll content decreased under the stress conditions in comparison to the control.

Generally, based on the results, maximum rates of microtuberization and viability were observed in Agria followed by HPS-II/67, and the highest microtuber weight was obtained in HPS-II/67 cultivar. When plants are faced to stress conditions like osmotic stress, free radicals such as reactive oxygen species (ROS) increases. On the other hand, plants use different strategies to scavenge the generated ROS. The reduction of chlorophyll content and increases of antioxidant enzyme activities are due to increase of ROS under osmotic stress conditions. At slight stress conditions, potato plants utilize the strategy to generate more tuber. Therefore, the lower concentrations of PEG can be introduced as a stimulator of microtuber.