جستجوی مقالات مرتبط با کلیدواژه « genetic variance » در نشریات گروه « زراعت »

Rice is one of the important and staple food crops in Iran, and its grain yield improvement has always been the most important objective in rice breeding programs. One of the important breeding methods in rice is crossing between selected varieties to develop recombinant inbred lines (RILs), and then identifying promising lines. This experiment was carried out with the aim of identifying high-yielding superior lines. One hundred forty one recombinant inbrd lines together with their parental cultivars were evaluated using randomized complete block design with three replications in research field of faculty of agricultural sciences, University of Guilan, Rasht, Iran, in 2018. Important agronomic traits were measured and recorded for all RILs. Analysis of variance showed that there was significant differences among RILs for all studied traits, indicating significant genetic variation among them. Estimated coefficients of phenotypic and genetic variations as well as variance components also showed that there was considerable variation among RILs population, particularly for number of filled and unfilled grains panicle-1, number of panicles plant-1 and grain yield. The narrow-sense heritability varied from about 20% for panicle length to 43% for grain width, days to maturity, and 1000-grain weight. Factor analysis showed that three main and independent factors explained about 96% of the total observed variance among RILs, and were the main reasons for significant relationships between traits. These three factors were deignated as yield and its components, grain appearance quality and phenological factors. Cluster analysis by UPGMA method classified the 141 studied RILs into three clusters. Cv. Sepidrood and cv. Gharib (parental cultivars) were grouped in the first and second clusters, respectively. Evaluation of the cluster values for different traits showed that the first cluster had the highest values for grain yield and its components and the third cluster for grain dimensions and appearance quality. In conclusion, the results of this experiment showed that there was significant genetic variation among the studied RIls. Therefore, successful improvement of important agronomic traits, particularly grain yield and its components, is feasible. The superior high-yielding lines with desirable appearance quality were also identified.

One of the methods that has been used in recent years to deal with dehydration and drought stress in many plants is the use of root symbiotic fungi (mycorrhiza). Ecological and physiological studies have shown that mycorrhizal symbiosis often results in better absorption of water and nutrients from the soil. Due to the importance of oilseeds and especially sesame, the study of commercial cultivars in terms of genetic variation, phenotypic components and heritability of traits is important. Sesame due to its high oil content (52-42 Percentage) and its proper quality (low cholesterol and the presence of some antioxidants) play an important role in human health and on the other hand the plant tolerates dehydration and drought stress. Currently, water stress is the most important and common factor in reducing yield in arid and semi-arid regions. High heritability for a trait indicates that the major part of phenotypic variance is due to genetic variance, while in low heritability, genetic factors have a smaller share in phototypic diversity. The aim of this study was to estimate the variance components and heritability of grain yield and related traits in 8 commercial sesame cultivars under different irrigation conditions.

In order to investigate the genetic diversity and the heritability of grain yield and yield components in sesame, 8 commercial cultivars were studied in three separate experiments using factorial split plot based on randomized block complete design with three replications in research field of Agricultural Research Center, West-Azerbaijan in 2015-2016 and 2016-2017 cropping seasons. The main plots (factor A and B) consisted of three different levels of irrigations (normal irrigation: irrigation after 70 mm evapotraspiration of crop or ETc, moderate drought stress: irrigation after 90 mm ETc and severe drought stress: irrigation after 110 mm ETc) and factor B included three levels: two species of mycorrhiza fungi Glomus mosseae, Glomus intraradices and non-inoculated (control). Sub plots (factor C) consisted of eight commercial cultivars of sesame.

The results of analysis of variance showed that the effect of environment, genotype and the interaction of environment × genotype on most of the studied traits were significant. In optimal irrigation regimes, moderate and severe drought stress under inoculation and non-inoculation conditions with mycorrhiza, the highest genetic variance was observed in biological yield, number of seeds per square meter and seed yield, respectively. The highest heritability in optimum irrigation conditions without mycorrhiza inoculation of traits (seed yield and number of grains per capsule), in optimum irrigation conditions and inoculation with mycorrhiza (both two species) (seed yield and 1000 seed weight), in moderate drought stress conditions and no inoculation with mycorrhiza (seed yield, 1000 seed weight and number of seeds per capsule), under moderate drought stress and inoculation with mycorrhiza G. mosseae (1000 seed weight and number of grains per capsule), under moderate stress conditions and inoculation with mycorrhiza G. intradices (seed yield, 1000 seed weight and number of grains per capsule), under severe drought stress conditions and without inoculation with mycorrhiza (stem diameter and 1000 seed weight), under severe drought stress conditions and inoculation with mycorrhiza G. mosseae (stem diameter, number of seeds per capsule and number of seeds per square meter) and in conditions of severe drought stress and inoculation with mycorrhiza G. intraradices (stem diameter, number of seeds per square meter and 1000 seed weight) were observed. Seed yield, biological yield and seed yield components had high genetic gain and genetic advance in all three different irrigation conditions. Among the components of grain yield, considering that the heritability of number of seeds per capsule and 1000 seed weight in all three different irrigation conditions is higher compared to the number of capsules per plant, so selection through number of seeds per capsule and 1000 seed weight to increase seed yield will be more efficient.

Therefore, commercial sesame cultivars that have more seeds per capsule and a 1000 seed weight can be used in breeding programs to produce cultivars with high seed yield. According to the information of this study, only general heritability can be calculated, but since many studies on commercial sesame cultivars in interaction with different conditions of irrigation and inoculation and non-inoculation with mycorrhiza have not been done, so this study can useful for researchers.

In order to determine the genetic parameters and heritability of different traits of sugar beet and also the relationship between traits, full-sib and hybrid genotypes were evaluated in separate trials at Miandoab Agricultural Research Station under salinity and normal conditions in 2017. In full-sib trial performed under salinity condition, root yield, sugar yield, white sugar yield, leaf relative water content, root dry weight, and root/shoot ratio, and under normal condition, root yield, sugar yield, root/shoot ratio and specific leaf weight had higher genetic variance than environmental variance and consequently had higher broad-sense heritability. In hybrid trial performed under salinity condition, for white sugar yield, potassium content, potassium/sodium ratio, nitrogen content, and leaf area, and under normal condition, for root yield, sodium content, potassium/sodium ratio and nitrogen content, genetic variance was high and as a result, broad-sense heritability was above 0.5. Therefore, these traits can be considered in breeding and selection programs. Under salinity condition, the narrow-sense heritability ranged from 0.16 to 0.66. The highest narrow-sense heritability was related to molasses sugar with 0.66, nitrogen content with 0.43, sugar yield with 0.38 and leaf relative water content with 0.38, respectively. Therefore, it can be concluded that these traits are partially controlled by additive effects and can be used for selection of different degrees. Under normal condition, the narrow-sense heritability ranged from 0.01 to 0.29 and the relative water content with 0.29 showed the highest heritability. Under salinity stress, heritability of root yield and sugar yield was moderate; so yield could be improved by long-term selection and hybrid production. The results of regression and path analysis showed that under salinity and normal conditions, when the root yield was considered as dependent variable, specific leaf weight, leaf area, and relative water content explained the variation among which the leaf area had the highest positive direct effect on root yield.

Improving crop yield under drought stress conditions is one of the most important goals of plant breeding. Drought tolerance is usually evaluated by plant yield under low water stress, but due to the influence of other traits under stress conditions, this trait alone cannot indicate drought tolerance of genotypes. Therefore, it is better in breeding programs to identify drought tolerance traits of genotypes and guide programs based on yield and other important physiological and biochemical traits. Determining the values of genetic variance and the additive part and the dominance of genetic variance in controlling traits under both normal and stress conditions is the basis for deciding how to use germplasms in different conditions, which researchers use based on different methods to estimate them. The aim of this study was to estimate the genetic parameters of quantitatively yielding and qualitative traits of sugar beet under drought and normal stress conditions for use in breeding programs.

To determine the genetic parameters of different quantitative and qualitative traits of sugar beet, two series of genotypes full-sib and hybrid (resulting from the meeting of some of full-sibs as paternal lines and two lines SC C2 and SC 261 as maternal lines) were studied under both drought and normal conditions, in Motahari's Research, Karaj in 2017. After testing, different physiological and qualitative traits of genotypes were measured in two environments and finally genetic parameters were calculated.

In full-sib experiment under stress conditions, sodium content, potassium/sodium ratio, nitrogen content, alkalinity coefficient, syrup purity, molasses sugar, leaf area, shoot fresh weight, shoot dry weight, root dry weight, root mass ratio, and root/stem ratio had more genetic variance than environmental variance, so they also had higher broad sense heritability. Therefore, due to high genetic variance, these traits can be used in breeding and selection programs. Under normal conditions, the amount of genetic variance was low in all traits and consequently, the general heritability was low. In hybrid experiment under stress conditions for sugar yield traits, sodium content, sodium/potassium ratio, nitrogen content, and leaf area, and normal conditions for sugar yield and sodium/potassium ratio there was high genetic variance and broad-sense heritability was observed above 0.5. Therefore, these traits can be considered for breeding and selection programs. In drought conditions, the highest heritability was related to potassium content 0.77, molasses sugar 0.65, extractable sugar percentage 0.48, syrup purity 0.44, and sodium content and relative water content with 43, respectively. So, these traits were controlled to varying degrees by additive effects. Under normal conditions, pure sugar with 0.4 and sodium with 0.44 showed the highest heritability.

The results showed that the genetic parameters calculated in the stress environment cannot be generalized to the non-stress environment. As a result, studying the genetic characteristics of lines and hybrids under different environments is inevitable so that the estimation of gene function can be more accurate.  In both environments, the narrow-sense heritability of root yield was low but in sugar yield was moderate. So, in improving root yield, hybrid products can be used, and in sugar yield, selection can be used in long and term generations, as well as hybrid production.

Drought stress is a limiting factor for sunflower. Various reports have mentioned the effect of water stress and limited irrigation on sunflower for many respects, including phonological traits, morphology, agronomic and physiological. Sunflower is a crop that can withstand a variety of environmental conditions, particularly drought and due to the developed root system. It has high efficiency in absorbing water from the soil. Sunflower is one of the most important oil crops and due to its high content of unsaturated fatty acids and a lack of cholesterol, the oil benefits from a desirable quality. The aim of this study is to investigate the genetic diversity and the heritability of agro-morphological traits in confectionary sunflower under different levels of drought stress. 56 local populations were studied in three separate experiments in rectangular lattice design (7×8) with two replications at Agricultural Research Center of West-Azerbaijan province, Urmia, Iran in 2012. Water treatments were well-watered, moderate and severe water stress conditions so that irrigation was applied with 50%, 70% and 90% depletion of available water, respectively. Various agronomic and morphological traits were calculated based on measuring traits in sunflower. Productivity effort as a physiological trait was measured by dividing the total dry weight of reproductive organs (head) to the total dry weight of plant. The results showed that in all three different water treatment conditions, heritability of head diameter, stem diameter, plant height, grain and biological yield was more than other traits. In well-watered conditions, moderate heritability varied between 0.52% for number of seeds per head to 80.61% for plant height. In moderate drought stress condition, the maximum and minimum heritability belonged to head diameter (76.21%) and chlorophyll index (26.45%), respectively. In severe drought stress condition, the most and the least heritability was observed for stem diameter (83.64%) and number of seeds per head (0 %), respectively. Among yield components, the heritability of 1000-grain weight at three water treatment conditions was higher compared to number of seeds per head, so for increasing grain yield, selection via 1000-grain will be more efficient. For the traits of grain yield, head diameter, stem diameter, biomass yield, chlorophyll index, dry weight of leaf, head and head with grain, the heritability in severe drought stress was higher than optimum conditions and this showed that the phenotypic variance is a large proportion of the genetic variance of more favorable traits. Due to the fixed component in the numerator and the denominator of genetic variance, environmental variance decreased in drought stress conditions in comparison with optimum irrigation conditions.

The theory and analysis of diallel crosses have been defined and developed by many scientists. Griffing in 1965 described the diallel analysis in four methods with four models. In this study estimation of genetic parameters through different methods of Griffing approach was compared. Seven lines of Brassica napus L. were crossed in all possible combinations including reciprocal crosses. Forty two F1s together with seven parents were planted using randomized complete block design with 2 replications. Combining ability analysis was carried out for 12 agronomic characters on the basis of four methods of Griffing’s approach. Estimation of additive (σA2) and dominance (σD2) genetic variances and calculation of dominance ratio (σD2/σA2) was carried out for these methods. The estimation of additive and dominance genetic variances in the method 3 were negative for all characters and in method 2 and 4 they were negative only for some characters. However, in method 1 additive genetic variance was positive for all characters. Considering the estimation formula for additive and dominance genetic variances it was concluded that, when mean square specific combining ability (SCA) is greater than mean square of general combining ability (GCA), estimation of additive genetic variance is negative. This situation was observed in methods 2, 3,and 4 but not in method 1. It was indicated that components of genetic variances was better estimated in method 1 than the other methods in this study. Results indicated that the method 1 provided consistent estimation of additive and dominance genetic variance and was superior in comparison with the other Griffing methods.