فصلنامه تحقیقات غلات
سال سیزدهم شماره 2 (تابستان 1402)

Drought stress is one of the most important environmental stresses in different regions of the world, which causes the instability of crop production. More than 20% of the world's agricultural lands are affected by moderate to severe drought stress. The seed filling stage is the last stage in the plant development and the most important stage in the accumulation of dry matter in the seed. Seed filling rate and period and the effect of various environmental and agronomical factors on these two important parameters affecting seed weight can be predicted using the mathematical models. Quadratic, polynomial cubic, and logistic models are among the mathematical models that have been used efficiently to predict the grain growth process. The purpose of this research was to investigate the grain growth process and the accumulation of photosynthetic substances in the grain of different wheat cultivars under non-stress (control) and late season drought stress conditions using mathematical models and to investigate the effect of grain growth parameters on grain yield.

This experiment was conducted as split plots based on randomized complete block design with four replications in the research field of Faculty of Agriculture, University of Zanjan, Zanjan, Iran, in 2018-2019. Normal irrigation (control) and drought stress after flowering were considered as main factor and four wheat cultivars (Shiraz, Marvdasht, Azar2 and Roshan) as sub-factor. Drought stress was applied by interrupt irrigation until the soil water potential reached about -2 MPa. To investigate the grain growth process, samples were taken from the main spikes after flowering every week. After drying the spikes, the grains were separated from the spike, the weight of single-grain was calculated, and the grain growth process was investigated using different mathematical models. To determine the best model, various statistical indices including root mean square error (RMSE), corrected Akaike (AICc) and ∆i were used, and the model with the lowest values of these indices was selected as the best model. Then, maximum and average grain filling rate, and grain filling period was estimated using the best selected model. The traits of plant height, main spike length, grain yield, biological yield and harvest index were also measured in addition to the grain growth process.

Comparison of different models using RMSE, AICc and i∆ indices showed that Darroch and Baker model (model number one) was the best model to evaluate seeds growth process in this research. Investigating the growth of grains with this model showed that the final grain weight decreased in all cultivars under drought stress conditions, and according to the prediction of this model, the lowest and highest final grain weight was belonged to Azar2 and Shiraz, respectively. Grain filling period decreased by 9.3% under drought stress conditions, and Shiraz (42.3 days) and Azar2 (34.4 days) had the highest and lowest grain filling period, respectively. Drought stress also reduced photosynthetic rate, leaf area durability, and number of grains per spike, but average and maximum grain filling rate were not affected by drought stress, which is probably due to the increase in the remobilization of photosynthetic materials under drought stress conditions. A positive and significant correlation was observed between grain filling period and grain yield under drought stress (r=0.375) and control (r=0.634) conditions. It can be concluded that the grain filling period was more important than the grain filling rate in this research. Drought stress decreased 1000-grain weight of the studied varieties by 18.3%, and Azar2 (47.70 g) and Marvdasht (33.50 g) had the highest and lowest 1000-grain weight, respectively. Grain yield and harvest index of the studied varieties also decreased by 40.8% and 22.4% under drought stress conditions, respectively, and Shiraz (4747.4 kg) and Azar2 (3179 kg) varieties produced the highest and lowest grain yield. Decrease in the harvest index indicated that drought stress reduced the grain yield more than the biological yield, which is probably due to the reducing of the grain filling period as well as disturbance in the grain filling process.

The results of this experiment showed that late season drought stress significantly reduced the photosynthetic rate, leaf area durability, number of grains per spike, 1000-grain weight and grain filling period, and finally led to a decrease in grain yield of the studied cultivars.

Sarri and Prescott scale (A) is one of the most popular scales for measuring foliar diseases of small-grain cereals, which is expressed as 0-9 scores. Double digit scale (AB) was created from incorporating A and B (disease severity on top leaves) scales. A and AB scales are considered as ordinal rank scales, and their recorded data (as descrete variables) can not be analyzed by parametric statistical methods. If they are suitably transformed to disease severity index (or percent of disease index = PDI), then can be analyzed by parametric methods as continous variable. The objectives of this study were to compare different methods and scales for measuring the disease severity, statistical analysis, advantages and disadvantages, and finally to introduce the appropriate method for evaluating the wheat tan spot disease caused by Drechslera tritici-repentis and other foliar diseases of small grain cereals.

In this experiment, the intensity of tan spot disease on ten wheat cultivars was measured in a randomized complete block design with three replications and recorded as four variables, A, B, AB and PDI. In this study, the first variable (A) was used to show the severity of the disease based on the Surrey and Prescott scale (equivalent to the first digit of the double-digit scale), and the second variable (B) to express the contamination level of the disease severity on top leaves (equivalent to the second digit of the double-digit scale). The third variable (AB) was obtained from the combination of the first and second variables, and the fourth variable was the percentage of disease severity index (PDI). To compare variables and sselect the best ones, statistical analysis of data was performed using descriptive statistics, analysis of variance, comparison of means by LSD method, as well as correlation coefficients and regression analysis between the studied variables.

Evaluating the skewness and kurtosis statistics of the studied four variables in this research showed that only the B and PDI variables had a normal distribution. Shapiro-Wilk and Kolmogorov-Smirnov statistics and data frequency distribution chart also showed the normality and continuity of two variables B and PDI, while the variables A and AB did not have a normal distribution and due to the gaps created between different data groups in frequency distribution chart, they can be considered as discrete variables. The results of analysis of variance indicated a significat difference between the studied treatments (wheat cultivars) in terms of two variables B and PDI, but the difference between wheat cultivars was not significant for the variables A and AB. Estimating the relationships between four variables using correlation coefficients and linear regression analysis revealed a significant relationship between the variables A and AB as well as the variables B and PDI. The results of linear regression showed that although the double-digit scale is a composite scale, there was a very strong regression relationship between its values and the variable A, while the relationship between the double-digit scale and the variable B was weak. On the other hand, PDI, which is the most complete variable to describe the disease severity, showed a strong regression relationship with the second digit of the double-digit scale (variable B), but its relationship with the first digit or numerical value of the double-digit scale (variable A) was weak.

The results of the statistical analysis of this research showed that the expression of disease severity (untransformed data) in terms of the variables B (disease severity on the upper leaves) and PDI (disease severity index) had more statistically appropriate than the variables A (Sari and Prescott scale) and AB (double-digit scale). Therefore, improving and upgrading the Sari and Prescott scale to a double-digit scale can only be effective in practice if it is correctly transformed into a comprehensive disease index (such as PDI), otherwise there will not be a big change in the quality of disease assessment. It is concluded that in assessing the severity of wheat leaf diseases, after determining the disease severity based on the A or AB scale, the data must firstly be converted to the variable PDI and then the analysis of variance or regression analysis should be performed.

The first step in breeding programs is accurate identification and sufficient knowledge of genetic parameters, including the type of gene action and the heritability of the studied trait. Development of high yielding lines and the identification of heterotic groups are the most important objectives of corn breeders. Also, determining the inbred lines of parents that create suitable hybrids is very valuable and can reduce the duration of the hybrid production program in corn. Graphic diallele analysis is one of the biometric methods of genetic analysis of quantitative and multigenic traits, the results of which can be very useful for improving traits within and between populations as well as producing hybrid varieties. The objective of this experiment was to investigate the genetic control of grain yield and related traits in maize inbred lines. The results of this study can be useful in selecting the most appropriate breeding method for the studied traits and producing high yielding maize hybrids in Zanjan region, Iran.

To estimate the type of gene action, the number of genes, heritability and other genetic parameters controlling grain yield and its related traits in maize inbred lines, a 5×5 diallel crosses design was used. The parents and 20 hybrids derived from their crosses were evaluated in a randomized complete block design with three replications in the research field of Zanjan University, Zanjan province, Iran, in 2019. The studied traits were including plant height, ear length, number of grain rows in ear, number of grains per row, 300-grain weight, and grain yield. The genetic analysis of the data was done according to Hayman (1954) graphical approach.

Estimating the genetic parameters showed both additive and non-additive gene effects in controlling the studied traits in this research. The results of graphical analysis also indicated the existence of over-dominance gene effects in controlling grain yield and its related traits. The alleles increasing the studied traits were of dominant type. Broad-sense heritability varied from 54% for 300-grain weight to 89% for ear length, and narrow-sense heritability ranged from 29% for 300-grain weight to 41% for number of grain rows per ear. Although high general heritability was estimated for most of the studied traits, which indicates the greater role of genetic factors and the relatively less influence of environmental factors in controlling the diversity of these traits, the existence of over-dominance effect of genes and low narrow-sense heritability indicates that the selection of these traits in the early generations will not be successful. Therefore, the breeding methods based on hybridization and selection in advanced generations can be useful in improving and breeding the grain yield and its related traits in the studied maize inbred lines. Also, the use of EP80 inbred line which had the most number of dominant genes for controlling yield and its components may have promising results in improving these traits in breeding programs.

In total, the results of the current study regarding the type of gene action controlling grain yield and its components in the studied maize inbred lines showed the important role of the over-dominance effects of genes. Therefore, the most appropriate strategy for exploiting these genes and improving the population is to obtain hybrid varieties that provide the possibility of exploiting heterosis in the investigated parents. is to use the heterosis phenomenon and produce hybrid varieties.

Maize as a tropical cereal is a main source of food for humans and livestock, as well as biofuels and fiber in some regions of the world. Increasing maize production is one of the main priorities of the country, Iran. One of the columns of increasing production is development of new high-yielding cultivars. To improve a complex trait such as grain yield that has low heritability, indirect selection by other traits or developing a suitable index based on several traits can be used. In this study, linear phenotypic selection index (LPSI) and linear molecular selection index (LMSI) were prepared using the combination of morphological traits and informative ISSR molecular markers. The objective of the present study was to prepare appropriate selection indices in maize to improve grain yield.

The plant materials of this research were 97 maize genotypes that were cultivated in a randomized complete block design with six replications in the research field of the Faculty of Agriculture, Urmia University, Urmia, Iran. Morphological traits were measured from the tasseling stage to the physiological maturity. Sixty ISSR primer combinations were also used to prepare the molecular profile of the studied maize genotypes. To select the suitable genotypes, two indices including linear phenotypic selection index and linear molecular selection index were used, and the efficiency of the indices was compared with the estimation of different parameters such as the rate of genetic gain and response to selection.

The results of the linear phenotypic selection index showed that the highest rate of genetic gain based on the index (DG) was observed for chlorophyll content (99.15) and the lowest one for number of ears per plant (0.01). The expected genetic gain for all studied traits (DH) and response to selection was estimated at 163.2234 and 0.774, respectively. Based on the linear molecular selection index, the highest rate of genetic gain (DG) was observed for leaf area (99.31) and the lowest one was observed for number of ears per plant (0.02). The expected genetic gain for all studied traits (DH) and response to selection was also estimated at 50.972 and 0.774, respectively. The results showed that the correlation between index and breeding value (rHI) in the LPSI index was relatively favorable (less than one), and in the LMSI index was optimal (one), but both correlations were significant at 0.05 probability level according to the t-test. However, the efficiency of selection based on the index (ΔH) was 163.22 for the LPSI index and 50.97 for the LMSI index. On the other hand, the degree of genetic gain of trait (DG) was different depending on the type of index. For example, the ratio of genetic gain (DG) derived from molecular to phenotypic index for the number of ears per plant and grain yield (2.00 and 1.28, respectively) was higher than the other traits. Also, the best genotype based on both indices was genotype number of 61.

According to the results obtained from the present study and the review of sources in this field, it seems that it is possible to benefit from the advantages of development of the LMSI index in the breeding programs in early generations, but in advanced generations, it is better to select genotypes using the LPSI index, in which case the cost of molecular evaluations will be reduced.

Fusarium verticillioides (Sacc.) Nirenberg causes maize ear rot in all maize-growing regions of the world and produces mycotoxins that contaminate maize grains. Therefore, it is considered an important species in terms of food health for both animal and human in the world. One of the best approaches to address this disease is to identify highly tolerant or resistant genotypes that can be used for genetic improvement. In this experiment, the resistance of 16 late maize hybrids was evaluated for cob resistance, silk channel resistance, and resistance in the germination stage using three inoculation methods. The objective of the current study was to select the genotype with high resistance in all three developmental stages.

The seeds of 16 late maize hybrids were obtained from the Maize and Forage Crops Research Depatment (MFCRD), Seed and Plant Improvement Institute (SPII), Karaj, Iran, and were planted in a randomized complete block design with three replications in the research field of MFCDR, in 2021. To inoculate the plants, the Kj7 isolate collected from infected maize cobs in the field of MFCDR was used. Maize hybrids were screened with three methods. In the first method, the resistance of the studied hybrids was evaluated by the rolled paper method at the germination stage. In the second method, the cob resistance was assesed by creating a wound in the middle of the cob and injecting spore suspension, and in the third method, silk channel resistance was investigated by injecting spore suspension into the silk channel seven days after the appearance of silks. Data statistical analysis was done by analysis of variance and comparison of means with Duncan's test using SAS software.

The results of analysis of variance and comparison of means showed that there was a significant difference among the studied 16 maize hybrids in terms of disease resistance with all three methods of artificial contamination. According to disease severity measurement in all three evaluated methods, the hybrids H3, H8, H11, H12 and H13 were selected as hybrids with high resistance against pathogenic fungi. These hybrids showed suitable resistance against all main methods of fungal infection and were superior hybrids compared to the other hybrids evaluated in this study in terms of resistance to maize ear rot caused by F. verticillioides. The implementation of these screening assays in maize breeding programs can be effective for classifying the degree of flexibility of maize germplasms to fusarium head rot.

The results of this experiment indicated that to evaluate the fusarium ear rot resistance of maize genotypes, the cob resistance method can be used as the main evaluation method especially in dry regions. Silk channel resistance can be used as a control method to evaluate the possible sensitivity of resistant or semi-resistant genotypes in humid areas where contamination with this method is important. Also, due to the different reaction of a number of hybrids investigated at the germination stage in this study and the possibility of the fungus growing as an endophyte in the plant, it is recommended to evaluate the new cultivars being introduced at this growth stage. Finally, hybrids should be introduced as resistant to this disease, which have shown a suitable reaction to the fungus in all three methods.

Cultivating forage plants is an important way to address the problem of a lack of forage and its consequences, which can be beneficial to the economy and improving food security. Millet is an excellent source of forage for livestock because of its high dry matter production, low water footprint and adaptability to different environments. However, there is not available well documented experimental results on the crop planting date for Rasht, Guilan province, Iran. Therefore, this study was performed to evaluate the impact of various planting dates on the crop grain and biomass yield in Rasht, which could be extended to similar regions.

To investigate the impact of various planting dates on the grain and biomass yield of proso millet (cv. Pishahang) in the climatic conditions of Rasht city, an experiment was conducted in a randomized complete block design with four replications in the research field of the Faculty of Agricultural Sciences, University of Guilan, Rasht, Iran, in two cropping years, 2016-17 and 2017-18. The experimental treatments in both years were four planting dates, May 29, June 27, July 29, and August 29 in the first year, and June 4, July 7, August 5, and September 6 in the second year. The central rows of each plot were used to measure grain yield and biomass respecting the margin effect, and recorded in terms of kg.ha-1. We tracked the growth of the leaf area over time by measuring leaf area and maximum leaf area index from tillering stage to final harvest. The SAS software was used to analyze variance and compare data values.

The results of the study showed that the interaction between planting date and year had a significant effect on biomass yield, grain yield, harvest index, leaf area index, panicle weight, panicle number, grain number, and a 1000- grain weight. In the first year, planting millet on May 29 resulted in the highest biomass (9927 kg.ha-1), grain yield (2182 kg.ha-1), panicle dry weight (25.53 g.plant-1), panicle number (15.08 per plant), grain number (2121 per plant), 1000-grain weight (5.23 g), and leaf area index (4.9). This was likely due to the favorable temperature conditions at that time of year. In the second year, planting millet on July 7 resulted in the highest biomass yield (6537 kg.ha-1), grain yield (1283 kg.ha-1), panicle dry weight (11.77 g.plant-1), panicle number (6.75 per plant), grain number (1345 per plant), 1000-grain weight (4.7 g), and leaf area index (3.69). This was likely due to the favorable meteorological parameters at that time of year, such as maximum and minimum temperature (30.24 and 21.46 0C, respectively), solar radiation (17.7 MJ.m-2.day-1), and sunshine hours (7.67 hours).

Overall, the results of the study suggest that planting millet in the period from June 4 to June 27 will result in the highest dry matter and grain yield in the Rasht region.