فصلنامه تحقیقات غلات
سال دوم شماره 2 (تابستان 1391)

Rice cooking and eating quality are the most important factors for accepting a variety by consumers. To determine the accurate gelatinization properties of rice starch with Little and Differential Scanning Calorimeter (DSC) methods, this research was carried out on 10Iranian rice varieties. All varieties were similar in amylose content and gelatinization score with Little method. The starch properties such as gelatinization enthalpy (ΔH), onest temperature (T0), peak temperature (Tp), conclusion temperature (Tc) were measured by using of the curve derived from DSC. Analysis of variance showed significant differences between studied varieties for gelatinization parameters obtained from DSC method, but there weren’t the significant differences between varieties for gelatinization scores derived from Little’s method. The maximum and minimum enthalpy (ΔH) was observed in Domsorkh (11.48 j/g) and Hasssansaraee varieties (6.44 j/g), respectively, but Domsorkh and Hassansaraee varieties had similar scores for alkali spreading values from the Little’s method. In varieties with the same amylose content, lipid-amylose complex increase crystalline structure of starch so enthalpy for gelatinization will be increased. Data analysis showed that there was significant correlation between lipid content and enthalpy at 5% probability level. In mean comparisons between varieties, the minimum and maximum onest temperature (T0) were observed in Domsefid (64.82 oC) and Domsiah (67.7 oC) varieties, respectively. Also, there was the significant correlation between onest temperature and lipid content. Results from current research showed that the Little’s method is a rapid and economical method for selecting lines and varieties with suitable gelatinization properties (3-5 score), but DSC method can explain more details of cooking differences between varieties where Little’s method is unable to explain them.

Rice improvement for drought tolerance requires reliable assessment of diversity and genetic analysis of drought tolerance related indices in breeding populations. In this study, 150 F5 families derived from a cross between Sepidroud (Indica) and Gharib (Indica) varieties were evaluated to multi-trait mapping of genomic regions controlling drought tolerance indices in normal and drought stress conditions. Results of biplot analysis showed that stress tolerance index (STI), mean productivity (MP), geometric mean productivity (GMP) and harmonic mean (HM) are suitable indices to select the high-yielding genotypes in applied rice breeding programs. QTLs mapping for each index using composite interval mapping identified three, three, two and three QTLs for HM, MP, GMP and STI, respectively, but the joint-analysis data for investigate the genetic relationships between these indices using the multi-trait mapping showed that there are significant genetic relationships between studied indices, so none of these identified QTLs didn’t independently control an index and jointly controlled multiple indices. Results from current study showed that the multi-trait joint analysis not only identified additional QTLs, but also revealed the genetic relationship between different highly correlated traits at the molecular level.

The germination and emergence are the most critical stages of plant life, because seeds are exposed to unfavorable environmental factors at this stage and plant establishment is confronted with difficulty. Therefore, prediction of germination time is one of the main goals of simulation researchers. In this regard mathematical techniques such as determination of the best nonlinear regression function which can quantify response of germination rate to temperature and estimate the cardinal temperatures would be very informative about characteristics and plants thermal requirements at this stage. The present study was conducted using a factorial experiment arranged in completely randomized design with three replications in 2010. The experimental factors including 19 temperature levels (12-48˚C at intervals of 2˚C from each other) and six rice (Oryza sativa L.) genotypes namely Binam, Hashemi, Anbarbou (landrace varieties), Dasht, Gil3 (Iranian improved cultivars) and IR64 (IRRI improved cultivar). Analysis of variance showed that there are significant differences between studied genotypes and genotype×temperature interaction effect for germination rate. The models of beta, quadratic, curvilinear, dent-like and segmented were applied to describe the relationship between germination rate and temperature. The comparison of different criteria for evaluating of the studied models showed different precision of the fitted models so that the segmented model for Hashemi variety, the beta model for Dasht and Gil3 varieties, the curvilinear model for Anbarbou and IR64 varieties and the beta and curvilinear models for Binam variety were the better than the other models. Results of current study showed that the mentioned models and their estimated cardinal temperatures can be used to predict the germination time and simulation of the studied rice varieties.

To determine intra- and inter-specific competition between wheat and wild oat by reciprocal yield model and other competition indices, a pot factorial experiment based on completely randomized design with 4 replications was carried out. The treatments were including four densities of wheat and wild oat as additive series (0, 2, 5 and 8 plants/pot). Results showed that interspecific competition coefficient of wild oat on wheat was greater than that of wheat on wild oat. Both species had low intraspecific competition effects relative to interspecific effects. Wheat plants were more susceptible to intraspecific competition than wild oat and relative competitive ability of wheat was lower than wild oat. Therefore, wheat plants were more affected by wild oat plants comparing to wheat plants. Relative yield in studied mixed relations was less than 1 or equal 1 indicating that wild oat and wheat plants compete on the same resources. Based on relative crowding coefficients analysis, wild oat was competitor than wheat. According to relative competitive effects, competitive ability of wild oat regard to biological and grain yield were 3.48 and 2.9 times of wheat, respectively.

To study the effect of nitrogen application, cutting height of main crop and berseem clover intercropping time on quantitative and qualitative traits of ratoon and berseem, a split split plot experiment based on a randomized complete block design with three replications was performed during 2009-2010 and 2010-2011 cropping season. Three levels of N (0, 35 and 70 kg.ha-1), two planting times of berseem clover (simultaneous planting with main crop harvest and 40 days after harvest) and two cutting heights (10 and 40 cm) were considered as main, sub- and sub-sub- factors, respectively. Analysis of variance showed that the highest ratoon yield, days to 50% heading and harvest index were achieved to applying of 70 kg.ha-1 N and 10 cm cutting height, whereas the maximum of biological yield in both two years was obtained from 40 cm cutting height. The increasing of N fertilizer increased qualitative traits of ratoon grain including gelatinization temperature (GT) and protein content (PC), but amylose content (AC) and gel consistency (GC) were not significantly affected by the N content. The highest forage fresh and dry yield in both harvesting times of berseem clover were obtained by 35 kg.ha-1 N and 10 cm cutting height. The grain yield and qualitative traits of ratoon were not significantly influenced by planting time of berseem clover. The highest forage fresh and dry yield and fiber content was observed in first planting time of berseem clover. Results from this experiment showed that planting of berseem clover simultaneous with rice harvest specially with 10 cm cutting height and applying of N fertilizer as starter can be suitable to produce higher quality of ratoon grain and berseem clover forage in the studied region.