Effect of the Wild Eggplant Rootstock (Solanum torvum) on the Drought Tolerance of Tomato Based on the Growth Indecies and Physiological Parameters

Introduction Drought stress in tomatoes reduces fruit quality and yield, also fall leaves and cause of blossom rot. It has been reported that drought stress reduces cell division and causes the stomata to close, followed by a decrease in the flow of carbon dioxide to the mesophyll cells of the leaf. Several methods have been proposed to overcome the drought stress in tomato plants, which can be mentioned the use of drought tolerance genotypes, genetic engineering to identify drought resistant genes and transfer them to sensitive plants, as well as the use of tolerancet rootstocks. It has reported that type of rootstock can effected on tolerance of tomato plants to drought stress. For this reason, the present study was conducted to investigate the effect of wild eggplant rootstock on the drought tolerance of two tomato cultivars.   Material and Methods In order to find the effect of the wild eggplant rootstock on the tolerance of two tomato cultivars, a factorial experiment was conducted as completely randomized design with two factors. Factors were included irrigation period three levels of 3 (control), 6 and 9-day and grafting combination at 6 levels involved non-grafted Dafnis, non-grafted Isabella, self-grafted Dafnis, self grafting Isabella, Isabella grafted on wild eggplant rootstock (S. torvum), and Dafnis grafted on wild eggplant rootstock. The plants were exposed to drought for 54 days. At the end of experiment growth and physiological parmeters including leaf specific, plant height dry weight of shoot as well as photosynthesis parameters, RWC and plant nutrients were measured. The amount of leaf proline was measured according to Paquin and Lichasur methodusing a spectrophotometer at a wavelength of 515 nm. The phenolic compounds of the leaves were measured at a wavelength of 725 nm using a spectrophotometer (Isfendiyaroglu and Zeker, 2002). Also, the membrane stability index (ion leakage percentage) was measured according to Lutts et al.'s method (Lutts et al., 1996).   Results and Discussion The results showed that with increasing irrigation period decreased the most of vegetative parameters, photosynthesis pigments, and mineral nutrients, so that, the highest value was showed at the 3-day irrigation period and the lowest value was at the 9-day irrigation period. Shoot weight decrese is probably due to morphological changes in plant roots, which is a plant response to drought stress. The results also showed that the interaction of irrigation period and grafted combination on some vegetative and ecophysiological parameters was significant. The lowest dry weight of shoot was observed at 9-day of irrigation period in plants of Dafnis grafted on torvum rootstock., Tthe highest dry weight root volume, leaf potassium and phosphorous concentration were at the 3-day irrigation period in self-grafted Dafnis plants.The results also showed that the amount of phenolic compounds in plants of Isabella grafted on torvum rootstock was the highest in 9 days irrigation period which may be due to the rootstock effect on the synthesis of these compounds in the scion. According to the results, the concentration of leaf magnesium in non-grafted plants increased with the increase of the irrigation cycle from 3 days to 9 days, althougth no significant difference was observed between self-grafted and non-grafted plants. In the 9-day irrigation period, the highest concentration of leaf magnesium was observed to non-grafted Daphnis plants, which was significantly different from other grafting combinations compounds except Daphnis self-grafted plants.   Conclusion The results of the present study showed that drought stress had the greatest effect on dry matter, and the amount of photosynthetic indices and pigments in tomato plants. Based on the results of the present study, it was found that the most of the reduce vegetative and physiological parameters was observed in Daphnis cultivar grafted on the thorum rootstock, were significantly reduced compared to self-grafted or non-grafted plants, which it was due to the dwarfing effects of this rootstock or grafting incompatibility. According to the results of the present study, it can be postulated that in drought stress Isabella cultivars grafted on the wild eggplant rootstock had more growh than other combination grafting. Hence it proposed more studies in this case.