فصلنامه تحقیقات غلات
سال یازدهم شماره 3 (پاییز 1400)

Rice has a special role in the diet of Iranians. To meet the needs of the country, it is necessary to increase the production of this crop. Therefore, due to the limited cultivation area, increasing yield per unit area is a more appropriate method. One of the best methods to increase production is to reduce the yield gap. The present study was designed and conducted to estimate the rice yield gap in Iran in 2016. In this study, the climatic zones and reference weather stations of rice production in Iran were determined using the global yield gap atlas (GYGA) protocol. First, the actual yield of rice was extracted from the Iranian agricultural statistics. Then, potential yield in the main production areas of rice was estimated using the SSM-iCrop2 simulation model and management, soil and climatic data. Yield gap was calculated from the difference between the actual yield of farmers and potential yield. The actual yield of rice in the main climatic regions of this crop in Iran was estimated from 3.5 to 5.2 ton.ha-1 and the simulated potential yield from 6.3 to 9.5 ton.ha-1. Therefore, the yield gap varied from 2.1 to 5.1 ton.ha-1. The results of this study showed that if the yield gap of rice is reduced, its production can be increased from 2,440,000 tons to 4,103,000 tons and achieve the self-sufficiency in rice supply in the country.

One of the plant strategies against stresses, especially micronutrient deficiencies, is the use of enzymatic antioxidant defense system. To investigate the effect of Zn deficiency on the genes expression of carbonic anhydrase (CAN), peroxidase (PRX) and glutathione S-transferase (GST) enzymes in Zn-efficient (Hamun) and -inefficient (Hirmand) bread wheat cultivars, a factorial experiment was carried out in completely randomized design (CRD) with three replications in greenhouse. The cultivars were grown in Zn deficient (zero) and adequacy (5 mg Zinc per kg soil) conditions and relative expression of the studied genes was measured using real time PCR technique in root and leaf of the cultivars at two growth stages, one month after germination (vegetative stage) and 30 % of flowering (reproductive stage). The results revealed the highest increase in CAN  (211 fold) expression in the root of Zn-efficient (Hamoon) cultivar in the reproductive stage. A realtively high expression of this gene was observed in the leaf of both cultivars in the reproductive stage. The highest increase in PRX (187 fold) and GST (230 fold)  expression was observed in the leaf of Zn-inefficient (Hirmand) cultivar at the reproductive stage. Generally, the expression of all three studied genes in the root of Zn-efficient (Hamoon) cultivar in the reproductive stage was higher than those of Zn-inefficient (Hirmand) cultivar. Also, the CAN expression in the leaf of Zn-efficient cultivar was significantly higher than that of Zn-inefficient cultivar. In conclusion, the results of the current study show that in the reproductive stage, Zn-efficient cultivars can effectively face against stress-induced damages through increasing the expression of the above-mentioned genes in the roots under Zn deficiency conditions.

In some regions of Iran, drought stress generally reduces yield at the final stages of wheat growth. This experiment was performed to investigate the effects of vermicompost and zinc foliar application on yield, yield components and quality traits of bread wheat (Chamran 2) under terminal moisture limitation stress, during 2018-19 in the research farm of the faculty of Agriculture of Lorestan University. The experiment was carried out as split-factorial based on a Randomized Complete Block Design with eight treatments and three replications. The main factor was moisture limitation stress (full irrigation until the end of the growing season and cessation of irrigation from the beginning of grain filling) and sub-factors were vermicompost (no application, and application of vermicompost 5 t ha-1) and foliar application of zinc (distilled water and zinc sulfate solution 3/1000 (w/v) equals to 0.36 g zinc sulfate m-2). The results showed that moisture limitation stress significantly reduced the 1000-grain weight, grain yield, harvest index, and Falling number. Interaction of moisture limitation × vermicompost × zinc was significant for grain protein and Zeleny sedimentation. Application of vermicompost increased grain yield, biological yield, harvest index, grain protein and Zeleny sedimentation thereby improved quantity and quality of wheat grain particularly under non-moisture limitation condition. Zinc foliar application also significantly increased the grain yield, biological yield, grain zinc content, protein percentage and Zeleny sedimentation. Combined and separate application of vermicompost and zinc foliar application reduced the damage of moisture limitation stress on the quantitative and qualitative yield of wheat. Therefore, use of them is recommended as a crop management practice in Khorramabad climatic condition particularly where terminal moisture limitation stress is usually occur.

Fusarium head blight (FHB) is one of the most important diseases of wheat that is a suitable disease for forecasting. In order to determine the statistical relationship among disease occurrence and weather and crop variables, this study was conducted in Golestan, Mazandaran and Ardabil provinces during 3 years (crop years 2016-17, 2017-18 and 2018-19). Crop characteristics and disease severity were recorded in wheat fields around meteorological stations. Nine weather data was received from the stations as daily data and converted to 30 periodic variables. Integrating flowering start date and anthesis length in different years and regions calculated as 11 time and meteorological calendar variables and used in statistical analyses. Results of correlation tests of these variables with disease showed that the best window for disease prediction was B020 (20 days before anthesis) and ATX (average of maximum temperature), RD (number of rainy days), DD (number of dry days), ASHTR (average of special hydrothermal ratio) and NP80 (number of days with rain and relative humidity > 80%) showed the highest correlation with disease. Results of logistic regression and discriminant analysis for the selected variables as one, two and three showed that ATX was the best individual variable, and the best combination of two variables was ATX + NP80 and adding ASHTR to them did not cause significant increase in prediction efficacy. Therefore, logistic regression and discriminant analysis model of ATX and NP80 in 20 days before anthesis, introduced as the best model for forecasting wheat FHB.

Maize, or corn, as one of the staple food products and forage crop, in addition to having a high grain and biomass yield, is of particular importance in the supply of carbohydrates, edible oils, and renewable energy. The plant is grown under a wide range of climatic conditions and is relatively sensitive to salinity. The development of salt-tolerant varieties of plants is inevitable policy in response to the growing demand for food in sustainable agriculture system. In the present study, the genetic diversity of 86 maize lines was investigated using morphological traits in a randomized complete block design (RCBD) with three replications under normal and NaCl salinity stress (EC 8 dS/m) in potted conditions. The results showed that salinity stress led to a significant decrease in mean of grain yield (GY), flag leaf length (FLL), flag leaf width (FLW), flag leaf area (FLA), ear height (EH), leaf angle (LA), stem diameter (SD), potassium to sodium ratio (K/Na), relative leaf water content (RWC), and number of rows per ear (RPE). In contrast, salinity stress caused a significant increase in the mean of days to tasseling (DTT) and days to silking (DTS) compared to normal conditions. Grain yield showed a very high positive correlation with biomass yield (BY), number of grains per row (GPR), ear length (EL), ear diameter (ED), grain depth (GDE), and cob weight (CD) under both normal and salinity stress conditions. The results obtained from stepwise regression analysis using Mallows’ Cp, and path analysis showed that, traits include number of grains per row (GPR), hundred grain weight (HGW), grain width (GW), and total leaves (TL) under normal conditions and traits include number of grains per row (GPR), grain depth (GDE), cob weight (CD), and ear diameter (ED) under salinity stress conditions were the most important traits affecting grain yield (GY). The great amount of h2 communality of mentioned traits in factor analysis was in order to confirm these results. According to the results of factor analysis using parallel analysis and very simple structure criterion (VSS), four hidden factors were determined in both normal and salinity stress conditions, which explained 60% and 65% of the variability among the maize lines, respectively. Before conducting the cluster analysis, three clusters were determined as the optimal number of clusters by elbow, silhouette and Gap statistics methods in each of normal and salinity stress conditions. Then, hierarchical cluster analysis of the studied maize lines was performed based on measured traits using Ward’s minimum variance method. Therefore, in case of need for hybridization to achieve salt-tolerant maize hybrids and improvement of important agronomic traits, suitable parents can be selected from the first and third clusters using comparisons of mean of the traits in clusters under salinity stress conditions and also with the help of the biplot obtained from principal component analysis (PCA). Targeted crossbreeding between selected parental lines allows for further exploitation of phenomena such as heterosis and aggressive segregation.

Comprehensive information on the genetics basis of inheritance is important for breeding programs. Therefore, the present study was performed as a diallel cross using nine selected early maturity maize lines. Thirty-six hybrids resulting from their one-way diallel crosses were planted during the two crop years of 2020 and 2021 in a randomized complete block design with three replications. Based on a two-year combined analysis of variance, a significant difference was observed in the probability levels of one and five percent between the crosses for all studied traits. Diallel analysis by the fourth Griffing method showed that genes with additive and non-additive effects are involved in inheriting control of grain yield, plant height and ear height, but only genes with additive effects play a role in inheriting the traits of 1000-seed weight, grain moisture percentage and cob percentage. According to Baker ratio, the additive effect of genes has a greater role in controlling 1000-seed weight, cob percentage, plant height, grain moisture percentage, ear height and grain yield, because they explained high values of this ratio. The most desirable general combinator ability for grain yield were NK79 and KE 77008/1. Specific combining ability of grain yield of crosses KE 77005/2 × K 1263/1 and KE 76009/311 × K 1264 / 5-1 positive and significant was estimated. According to the results obtained for general and specific combining ability, the use of these lines and crosses in grain yield breeding programs will be promising.