Abstract
Variability in some physicochemical characteristics of 22 durum wheat (Triticum turgidum L. var. durum) cultivars was investigated. The experiments were carried out under rainfed conditions at an arid (Jordan University of Science and Technology [JUST]) and a semiarid (Maru) location in northern Jordan. Statistical analysis revealed significant differences among the cultivars for each characteristic. Location X cultivar interaction was significant for all characteristics except for SDS-SED. Results showed that the semiarid growing location (Maru) proved to be favorable for production of durum wheat higher in gluten, amylose, amylopectin, and milling yield.
INTRODUCTION
Durum wheat is the most important crop in Jordan in terms of acreage, and total yield gross value. The per capita consumption of wheat is about 170 kg/year, mostly as flat bread, and to lesser extent, as bulgar (boiled wheat grits) and farikah (roasted wheat at hard dough stage). Bread is the daily staple of the Jordanian people and provides most of their calories and proteins. Efforts are underway to improve wheat yield through breeding, and/or introducing high yielding cultivars. The goals are to meet the increasing demand for bread and reverse declining production. Environmental conditions exert significant influence on chemical composition of wheat Citation1-5.
The objective of this study was to investigate variation in some physical properties and chemical composition of seeds in 22 durum wheat cultivars grown under arid and semiarid Mediterranean environments.
MATERIALS AND METHODS
Plant Materials and Growing Conditions
The experimental material consisted of 22 durum wheat cultivars. Seeds of these cultivars were provided by the International Center for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria. Trials were conducted under rainfed conditions at semiarid (Maru Experimental Station; 34°40′N, 590 m altitude) and arid (Jordan University of Science and Technology [JUST] Experimental Station; 34°35′ N, 530 m altitude) locations in northern Jordan during the 1994–1995 growing season. The soil type was silty clay (fine, montmorillonitic, thermic, Entic Chromoxeret) at both locations. The JUST location typically experiences moderate to severe drought stress during grain-filling while at the Maru location moderate drought stress prevails during grain-filling. Both locations have a typical Mediterranean climate.
Seeds of the wheat cultivars were sown on November 20 and 23, 1994, at Maru and JUST, respectively. Plots were 1.2 × 4 m2 with 4 rows spaced 0.30 m apart and 5 cm between plants. Fertilizers were applied at sowing time at the rate of 40 kg N ha−1 and 25 kg P ha−1. Weeds were controlled by hand. At maturity (during the first 2 weeks of June), heads from plants in the two middle rows of each plot were harvested manually, sun-dried for 2 weeks, threshed manually, and sent to the laboratory for evaluation.
Physical Measurements
Hectoliter. The weight of 1 L was determined using a standard hectoliter apparatus.
Thousand Kernel Weight. The 1000-kernel weight was determined by weighing 1000 kernels.
Sodium Dodecyl Sulfate Sedimentation Value. The sodium dodecyl sulfate sedimentation test was determined using the method of Dick and Quick Citation[6].
Specific Gravity. Specific Gravity was computed from weight and volume of grains.
Milling Yield. Wheat samples were tempered to 15.5% moisture content, and milled into flour on a MLU 202 Buhler laboratory mill (Uzwil, Switzerland). The average flour yield and bran percentages were recorded.
Gluten Determination. Gluten was determined by washing wheat flour sample manually with distilled water to remove starch, and the average gluten weight was recorded.
Chemical Analysis
Grain samples (100 g) from each replication were oven-dried, and milled to pass a 0.5 mm screen in a Cycotec mill and prepared for chemical analysis. Moisture, protein (N × 5.7), fat, ash, and fiber contents were determined according to AOAC Citation[7] procedures. Carbohydrate (percent CHO) was determined by difference. Amylose contents were determined by using phenol-sulfuric acid reaction according to the method described by McCready et al. Citation[8]. Grain starch was determined by extracting with 80% ethanol, solubilizing with dilute perchloric acid, and starch was estimated colorimetrically Citation[8]. Amylopectin was computed by subtracting amylose from starch content.
Experimental Design and Statistical Analysis
The experimental design was a randomized complete block with three replications. The collected data were subjected to analysis of variance (main effects and interaction) and least significant differences (LSD) were calculated to determine the significance of differences between the means.
RESULTS AND DISCUSSION
Environmental-genetic interactions expressed as location by genotype (L × G) were significant for each trait except SDS-SED (Table ). All measured traits were significantly influenced by location and cultivar (Table ). Berke et al. Citation[9] suggested that significant L × G interactions indicate that cultivars respond differentially across environments.
Table 1. Probabilities of Significance of Mean Squares for Seed Physical Characters and Chemical Composition of Durum Wheat Cultivars
The locations differed markedly in hectoliter weight and 1000-kernel weight (Table ). Durum wheat cultivars grown at the semiarid location, Maru, exhibited lower protein and fat contents than those grown at the arid location, JUST. Moisture stress is known to elevated protein content Citation[10]. Thus, variation in the contents of different grain chemical components among locations may be attributable to variation in genotype or environmental factors. Rao et al. Citation[5] reported that grain protein contents in wheat varied under different environmental conditions. This study indicates that the environmental factors might have affected the assimilates transport to the grain and influenced chemical composition of grains. Data showed that the bran and milling yield varied significantly among cultivars and were slightly higher than those reported by Ereifej and Shibli Citation[11]. The SDS-Sedimentation as quality parameter of flour obtained from the investigated wheat cultivars is shown in Table . These values are lower than those reported previously Citation[11]. The variation in SDS-Sedimentation values of the tested cultivars might be attributed to the poor quality of their gluten Citation[12]. The wheat cultivars showed high amylopectin and low amylose contents. The starch usually varies in amylose and amylopectin content according to source of grain and genotype. The flour quality parameters (milling yield, percent gluten, amylose, and amylopectin) were found to be affected by genotype, growing location, and interaction (Tables and ).
Table 2. Effect of Location (L), Cultivar (C), and L × C Interaction on Some Characteristics of Wheat Cultivars
Table 3. Location (L), Cultivar (C), and L × C Effects on Bran, Milling Yield, Gluten, Amylose, and Amylopectin Content in Wheat Cultivars
The chemical composition of the wheat cultivars is presented in Table . Ash, fat, protein, fiber, and carbohydrate contents varied significantly among cultivars and location. Ash content values are comparable with similar values reported by Ereifej and Shibli Citation[11]. Fat, protein, fiber, and carbohydrate contents were slightly higher than those values reported previously Citation[11]. The reason is probably attributable to genotype and environmental factors.
Table 4. Effect of Location (L), Cultivar (C), and L × C Interaction on Chemical Composition of Wheat Cultivars
The extent of wheat genotypic variation in protein, fat, ash, and carbohydrate contents are illustrated in Table . Genotypic variation was relatively large for fat, fiber, and carbohydrate and relatively low for protein content in grain. The variation in chemical composition caused by environmental conditions (locations) was greater than the variation among the cultivars. The results showed that a considerable portion of the variation in protein and fat contents was attributable to cultivar differences in grain genetic background. Singhal et al. Citation[13] also demonstrated that the protein content of wheat grains decreases as grain carbohydrates increase. Durum wheat grown at Maru showed better chemical composition and higher flour yield than those grown at JUST.
In conclusion, the physical properties varied significantly and they were influenced by cultivar, location, and interaction. The chemical composition of durum wheat cultivars also was found to be influenced by wheat cultivar, growing location, and interaction.
ACKNOWLEDGMENTS
The authors are grateful to the Deanship of Scientific Research (JUST) for supporting this work. Thanks are also extended to the International Center for Agricultural Research in Dry Areas, Aleppo, Syria, for supplying the wheat seeds.
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