A field experiment was conducted in Dhaka, Bangladesh, geographical location is 20° 34’N- 26°38’N and 88° 01’E-92°41’E, mean humidity 79.5%, annual rainfall (average) 2000 mm and maximum annual temperature 36°C and minimum 12°C. The annual precipitation varies from 1500 mm in the north to 5700 mm in the northeast and during the periods from (November-March). The experiment was conducted to evaluate the fruit quality and osmotic adjustment in tomato plants due to water stress. Four varieties of tomato plants namely, BR-1, BR-2, BR-4, and BR-5 were the test crops. The seeds of four varieties namely BR-1, BR-2, BR-4, and BR-5 from the Bangladesh Agriculture Research Institute (BARI) at Gazipur. The soil used in the field experiment was of Tejgaon series under Madhupur tract (According to Reconnaissance Soil Survey report of Dhaka District, 1965 reviewed in 1987). For physical and chemical analysis soil samples were collected at a depth of 0-15 cm from the experimental station of Bangladesh Agriculture Research Institute at Tejgaon, Dhaka. Tejgaon soil has a wide range of crop potentialities and is best suited to producing dryland crops. This soil can be successfully used to study the effect of moisture levels on different cultivars of tomato. The collected soil samples were air-dried ground to pass through a 2 mm sieve and then mixed thoroughly to make a composite sample. Dry grasses and other vegetative residual parts were discarded from the soil. The general physical and chemical characteristics of the soil were: Textural class of soil-loam, sand - 35.80%, silt - 40.20%, clay - 24.00, Moisture at field - 32%, Moisture at wilting-10%, Maximum water holding capacity-45%, Hygroscopic moisture-1.73%, Bulk density-1.39 g/cc, Particle density-2.63g/cc, Porosity-47%, pH- 5.1, EC-90 µS, OM-1.1%, CEO- 14.88 meq / 100 g soil, and N-0.07%. The experiment was carried out in a randomized complete block design with four treatments and three replications for each cultivar. Unit plot size was 1 mX1 m with four plants per plot. The land was prepared well by harrowing followed by laddering. The grasses, weeds, and other vegetative residual parts were removed from the land. In this experiment spacing was 75 cm between plots, 50 cm between rows, and 45 cm between plants. Cow dung was applied at the rate of 6t/ha at the time of final land preparation. N, P205, and K20 were applied at the rate of 260-200-150 kg/ha, respectively. The entire amount of phosphate, potash, and half of the nitrogen was mixed at the time of the preparation of land. The rest half of the nitrogen was applied in two splits, one at 21 days after sowing of plants during the vegetative stage and another at the flowering stage. Seeds were sown at BADC (Bangladesh Agriculture Development Corporation) and after 25 days of germination, healthy seedlings of uniform size were transplanted in the field. After transplantation, Plants had been shaded for 4 days to protect them from sunlight. Twenty-one days after transplantation, each row of tomato plant was supported with a bamboo stick to prevent lodging. Weeding in the plots was done when necessary. As growth progressed, the tomato plants were invaded by insects. It was, therefore, necessary to spray the plants with Malathion (1 mI in 1 L water) as an insecticide. The insecticide was sprayed as and when required. The stress period with the cultivars commenced 28 days after transplantation. The water stress treatments were imposed at 82-100% (T0), 69-85% (T1), 53-67% (T2), and 40-50% (T3) of the field capacity, respectively, in order to investigate the fruit quality and osmotic adjustment of the plant. Soil samples were collected at 6 days intervals for measuring the soil moisture percentages from the plots and were measured gravimetrically by drying the soil samples at 105°C for 24 hours. To maintain the above-mentioned moisture levels, the soil was irrigated with the amount of water lost by evaporation and transpiration. By the addition of irrigation water after six days, the soil moisture levels were within the following ranges: 26-32% (T0), 22-27% (T1), 17-21% (T2), 13-16% (T3). Water was added weekly to maintain soil moisture at 40-50%, 53-67%, 69-85%, and 82- 100% of the field capacity throughout the experimental period. After the end of the experiment, the ripening of the tomatoes was observed and recorded. Young and fresh leaves were taken for biochemical analysis. Three leaves of tomato plants of each plot were wrapped in aluminum foil and stored in the deep freeze. These were done just after plucking the leaves from the plants. The riped tomatoes were harvested from time to time. After the harvest of the riped tomatoes, fresh weight was recorded and visual quality and physical damage of tomatoes were determined according to the rating, scale. Three tomatoes from each plot were cut into pieces for application of the rating scale for internal tissue damage due to bruising, the rest of the fruits were used for other biochemical investigations. Organic solutes like Glucose, fructose, sucrose, malic acid, L-ascorbic acid, and citric acid in tomatoes were determined by the enzymatic methods described. Proline in leaves was estimated by the method outlined. Three tomatoes from each plot were minced separately by an electric mixture and extracted with water (60°C). In the extract, the contents of glucose, fructose, sucrose, (with carrez - solutions) citric acid, and malic acid were analyzed by enzymatic methods. For the assay of ascorbic acid, fruit samples were well minced with an electric mixer and homogenized in metaphosphoric acid (15% w/v). The pH of the mixture was adjusted to 3.7 with KOH and ascorbic acid was determined by enzymatic methods (Boehringer- Mannheim 1989). Proline was estimated by the method outlined. For the determination of proline in tomato leaves, Purified Proline was used to standardize the sample values. Acid ninhydrin was prepared by warming 1.25 g ninhydrin in 30 ml glacial acetic acid and 20 ml 6M phosphoric acid, with agitation, until dissolved Kept cold (Stored at 4°C) the reagent remains stable for 24 hours. Approximately 0.5 g of plant material was homogenized in 10 ml of 3% aqueous sulfosalicylic acid and the homogenate was filtered through Whatman # 2 filter paper.
- Two ml of filtrate was reacted with 2 m 1 acid ninhydrin and 2 m 1 of glacial acetic acid in a test tube for 1 hour at 100°C and the reaction terminated in an ice bath.
- The reaction mixture was extracted with 4- mI toluene, mixed vigorously with a test tube stirrer for 15-20 sec.
- The chromophore containing toluene was aspirated from the aqueous phase, warmed to room temperature and the absorbance read at 520 nm using toluene for a blank.
- The proline concentration was determined from a standard curve and calculated on a fresh weight basis.
- To evaluate the quality parameters of the plant, enzymatic methods were used.
For the determination of glucose, fructose, sucrose, malic acid, and citric acid in tomato fruits, the following techniques are used for sample preparation. The sample was homogenized using a mortar, A well-mixed sample was accurately weighed and extracted with hot water (60°C). The extract was transferred quantitatively to a volumetric flask and filled up to the mark with redistilled water. Filtered and used the clear solution for the assay. For clarification (glucose, fructose, and sucrose) the following solutions are used 5 ml carrez-1 solution (3 60g potassium hexacyanoferrate-II, K4 [Fe (CN) 6] 3H2O/100 mI. 5 ml carrez-II solution (7.20 g of ZnSO4, 7H2O/100 ml and 10 ml NaOH (0.1 mol/L). L. Ascorbic acid: For the assay of ascorbic acid the tomatoes were well minced with an electric mixture and homogenized with metaphosphoric acid (1 5%WN). After mincing the pH of the mixture was adjusted to 3.7 with KOH solution. Finally, the results were analyzed statistically employing Duncan’s New Multiple Range Test (DMRT).