The effect of different concentrations of ascorbate (As) at 0, 0.25, 0.5 and 1.0 mM, salicylate (Sa) at 0, 0.25, 0.5 and 1.0 mM , in addition to silicate (Si) at 0, 100, 250, and 500 ppm on potato plant subjected to different water regimes; three days interval (control), four days interval (4DI) and five days interval (5DI).  Photosynthetic pigments, free proline and malonyldialdehyde (MDA) concentrations, and plant dry matter percentage were determined. Also, tuber yield was recorded and the percentage of tuber dry matter was determined. Water deficit resulted in significant reduction in tuber yield, plant dry matter percentage beside significant increase in free proline and MDA contents. Meanwhile, effects on photosynthetic pigments content and tuber dry matter were inconsistent. The effects of using different concentrations of ascorbate (As) under water deficit provide a superior effect of As at 0.25 mM. Data revealed that ascorbate treatment enhanced tuber yield by improved Chl (a and b) and carotenoids content, with a promoted reduction in free proline content and MDA. Salicylate (Sa) treatment under water deficit exhibited partial enhancement in photosynthetic pigments; where, Sa (1.0 mM) increased Chl a under all water regimes and Chl b at control and 4DI water regimes. While Sa (0.5 mM) improved carotenoids content at 5DI water regimes. The positive effect of salicylate on tuber yield was obvious only at 5DI water regime; as salicylate concentrations (0.25, 0.5 and 1.0 mM) enhanced tuber yield by 65.61, 21.8 and 33.33%. Data exhibited that these increments were concomitant with a  reduction in free proline content and a slight increase in tuber dry matter. Interactive effects of Silicate (Si)/water deficit were variable with the concentration under the used water deficit regimes, where, Si (100 ppm), showed higher means of Chl (a and b) with a reduction in free proline contents, at both 4DI and 5DI. The higher tuber yield resulted only at 5DI. More pronounced effect, Si (250 ppm) exhibited increment of photosynthetic pigments, plant dry matter, tuber yield, along with slight reduction in MDA, particularly at 5DI. It could be concluded that silicate treatment alleviated water stress by improving carotenoids content, plant dry matter and reducing both free proline and MDA contents, which attributes enhancement in tuber yield under water deficit. Generally, lower concentrations of As, Sa and Si showed their benefits under higher water stress regimes.

In this study, Two field experiments were conducted in Ourabi operation Farm, Cairo-Ismaellia desert road at Kalubia Governorate. The experiment was carried out during the two seasons of  2013/2014 and 2015/2016, to investigate the effect of  plant growth regulator (Mepiquat chloride) with three different potassium fertilizers sources [chemical potassium (KC), foliar potassium (KF) and rock potassium (KR)] on growth development and total yield in potato plants (Solanum tuberosum L. cv. Spunta) . Chemical potassium (control) with / without Mepiquat chloride achieved better plant height, no. of stem and leaf area/plant. Rock potassium with mepiquat chloride  obtained the highest productivity of fresh and dry weights, total tuber yield and yield components  (weight of tubers, size of tubers, diameter of tubers and number of tubers) following by foliar potassium with mepiquat chloride  compared with control treatment.