Fresh water resources are limited and their use in agricultural production is expected to come under increasing constraints. Eighteen Syrian lines of potato (Solanum tuberosum L.) were screened for drought tolerance by measuring aerial and root growth in vitro. Drought stress was evaluated by adding 2, 4, 6, 8 and 10 % (w:v) of sorbitol to MurashigeSkoog medium and compared to 0 % for the control. Water potential of media ranged from −0.58 MPa to −2.5 MPa. Water-stress in culture adversely affected plant growth, and genotypes differed for their responses. Plant length and stem thickness, leaf area, root number length and thickness, and plant fresh and dry weights and plant water content were measured and all decreased due to drought. Grouping lines by cluster analysis for response to drought resulted in: (1) a tolerant group of six lines, (2) a moderately tolerant group of seven lines, and (3) a susceptible group of five lines. The variation in germplasm indicated that potato varieties can be developed for production under some levels of drought.

). Finally, the highest percentage virus free plantlets of PVY (93% in Binella and 87% in Burren) were obtained from meristem-tips 100 µm in length excised a er electric treatments (15 mA/10 min).

The effect of different hermetic and non-hermetic closure-types (aluminum foil, cotton bung, cotton plug, polypropylene cap and Steristopper) on potato (Solanum tuberosum L.) plantlets growth and chlorophyll contents was studied in three genotypes belonging to different maturity groups. Plantlets grown in culture tubes closed with aluminum foils and polypropylene caps had higher fresh mass and shoot length, but lower chlorophyll contents, higher senescence index and various morphological abnormalities. Non-hermetic closures like cotton plugs and Steristoppers were found optimum for plant growth without any morphological abnormalities. Besides, these plantlets exhibited low senescence index and had higher chlorophyll contents that favour acclimation to ex vitro conditions.

The experiment was carried out with the aim of studying the effect of biological stress on some morphological parameters of ten varieties of potatoes grown in vitro. Biological stress was applied by adding different concentrations of fusaric acid (0, 0.0125, 0.025, 0.05, 0.1, 0.2 mM), to the growth medium MS, and some growth parameters were measured, such as plant height (cm), number of leaves (leaf/plant¹), leaf area (mm²), number of roots (root.plant¹) and length it (cm), wet and dry weight of the plant (g). The results showed that the studied varieties were different in the response to biological stress according to the studied parameters. The addition of fusaric acid led to reduce all growth parameters compared with the control. The cluster analysis showed that based on the sum of the relative values ​​of the studied growth parameters, the studied varieties were distributed in three different groups: The first group includes three tolerant varieties to biological stress, and these are Toronto, Barcelona, and Suria). The second group includes four Moderate varieties of bio-stress, and these are Fabulla, Nectare, Spunta, and Ardappel. The third group included the following sensitive varieties, 7-four-7, Farida, and Joly. The results indicate that the in vitro screening technology can be used as a fast and efficient method to investigate the genetic variation of biological stress tolerance in potatoes.

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