Our study indicates that jojoba is suitable plant for cultivation of the Egyptian marginal soils, in the desert area, where the seeds were germinated and grown in sandy soil of marginal fertility. To study the effect of NaCl and mannitol on seeds germination, jojoba seeds were placed on cotton layer flooded with solution containing different concentrations of them. Salinity stimulated seed germination, especially, when the seeds were subjected to relatively low concentration of NaCl (0.5 -3 gm/l). Increase the concentration of NaCl over 3 gm/l resulted in inhibition of seed germination as well as radicle growth. Application of 2 or 3 gm/l mannitol in germination medium improved the seed germination, vice versa was detected under progressive increase of mannitol in germination medium. Mannitol as same as NaCl delayed seed germination of jojoba plant. On the other hand, jojoba seeds can be germinated in low frequency under high concentration of mannitol, up to 100 gm/l, when seeds were placed on three cotton layers just wetted by distilled water containing mannitol. Temperature may be the most critical factor during jojoba seed germination, therefore summer was the best season for seed germination; also, 30 o C was the best temperature degree for seed germination and emergence of radical in the shortest time.

Several factors negatively affecting plant growth and production. Abiotic stresses play a vital role against many plant species. Among various abiotic stresses, heavy metals provide one of the most harmful effects on plant performance. Thus, this study was designed to establish an efficient in vitro protocol for chromium (Cr) toxicity tolerance screening in banana. One of the most important commercial banana cultivars (i.e., Grand Nain) was used. Five different concentrations of potassium dichromate (i.e., 50, 100, 200, 400 and 600 ppm) were tested along with free chromium medium as a control. Analysis of variance showed highly significant differences among Cr concentrations, affecting shoot length and number of shoots per explants, compared to control. In addition, results clearly showed the harmful effects of chromium on both shoot length and number of shoots per explant. In this regard, the percentage of reduction in shoot length due to Cr treatment ranged from 5.77 to 84.09% regarding treatment with 50 and 600ppm, respectively. Moreover, the number of shoots per explant was decreased by a range of 6.00 to 86.48% caused by treatment of 50 and 600ppm, respectively. According to these results and the analysis of variance, it is recommended to use the concentration of 400ppm potassium dichromate for in vitro screening of chromium tolerance in banana. The established protocol is efficient and of great importance and could be used for selecting chromium-tolerant genotypes in banana and other species.

Abiotic stresses have a significant negative impact on plant growth and production. Among which, toxicity of heavy metals is considered one of the most factors affecting plant growth and agriculture on new reclaimed lands. In this study, the harmful effect of chromium was evaluated on in vitro banana plants of Grand Nain and Williams-Zeef cultivars based on morphological, physiological, and molecular assessments. Results showed that chromium significantly decreased all studied traits, including plant fresh weight, plant length, number of shoots per explant, and photosynthesis related pigments (chlorophyll and carotenoid content). The percentage of reduction due to chromium treatment ranged from 36.48 to 79.69% in shoot length of Grand Nain and chlorophyll-b in Williams-Zeef, respectively. Both banana cultivars were negatively affected by chromium treatment. However, Williams-Zeef showed higher reduction than that of Grand Nain in all studied traits. On the other hand, molecular analysis was performed to detect any variation between chromium-treated and untreated plants using inter simple sequence repeats (ISSR) and start codon targeted (SCoT) polymorphism. Results of molecular analysis confirmed the morphophysiological findings, by detection some polymorphic bands due to chromium treatment. In this regard, a total of six polymorphic bands were detected in the two banana cultivars, discriminating treated and control plants. In agreement with morphophysiological results, Williams-Zeef showed more polymorphism (five bands) due to chromium treatment than Grand Nain (one band). The screening protocol used in this study was efficient and helpful and could be used in successive studies to evaluate other toxicants and with other plant species as well.