stepwise regression

Germination is one of the most important stages of crop plant growth and proper germination in a wide range of environmental conditions is necessary for plant establishment. In this research, 20 varieties of Iranian barley and 24 varieties of European barley were used in three salinity levels (100, 200 and 300 mM sodium chloride) and a control level (distilled water) in order to investigate the tolerance of salinity stress in the germination stage, as a factorial test based on a completely randomized design with three replications in the mushroom cultivation chamber with controllable temperature and light and sterile conditions in the Nosoud agricultural service center by a protein marker in the biotechnology laboratory of the agriculture and natural resources of Razi university. The results of analysis of variance of traits related to germination showed that the effect of salinity, cultivar and salinity × cultivar were significant for all traits. By increasing the salinity level from 0 to 300 mM, all traits and indices decreased except the average germination time. The germination percentage had a positive and significant correlation with the total seedling length, shoot length, seed germination index, average germination rate and germination rate index. Stepwise regression analysis of different traits with protein markers showed that there were 13 bands associated with different traits. The most significant correlation with traits was related to the 60 kDa marker which was related four indices of seed germ, average germination speed, shoot length and cleoptile length. After the validation studies and confirmation of the results, the identified markers can be used in marker-assisted selection for related traits.

Identifying selection indices is the most important step of a breeding project that aims to improve grain yield. The definition of the selection index is usually done by evaluating the variables in multivariate statistical methods. In the present study, the relationship between grain yield and its components in bread wheat genotypes was determined by multivariate statistical methods. The experiment was conducted in a randomized complete block design with 3 replications in the research farm of Gorgan University of Agricultural Sciences and Natural Resources in the 2018-19 crop years. Ten commercial cultivars of bread wheat along with their offspring from direct and inverse crosses in a dialysis arrangement were evaluated for morphological and phenological traits, especially grain yield and its components. The results of genotypic and phenotypic correlation coefficients showed a positive and significant correlation (at 1% probability level) between grain yield and spike length, spike weight, number of fertile tillers, number of seeds per spike, number of spikes per spike, 1000-seed weight, biological yield and harvest index. Based on the results of stepwise regression analysis, biological yield, harvest index, number of grains per main spike and main spike weight were entered into the regression model, respectively, and explained a total of 98% of the variation in grain yield. Based on the results of path analysis, biological yield had the highest direct effect on grain yield. After biological yield, the most direct effect on grain yield was related to the weight of main spike. Also, by considering eigenvalues greater than one in factor analysis, 8 hidden factors were identified that explained a total of 75.18% of the data changes. In general, it can be concluded that biological yield, harvest index, number of seeds per spike and weight of spike compared to other traits can be used as appropriate indicators in breeding programs to select high-yield genotypes in field conditions. Genotypes Alo, Ehsan♂ × Gonbad♀ and Ehsan had the highest value for the studied traits, which can be used in future breeding researches.

To evaluate the genetic variation of Rosa damascena as an important aromatic and medicinal species, 38 genotypes of this species were studied for the diversity of phenological and morphological traits (flowering period, plant height, canopy diameter, number of leaves at the plant, total green area of the plant, number of flowers per plant, fresh weight and percentage of dry matter content of flowers and flower yield per plant) in a randomized complete block design with three replications in Zalleh Research Station of Sanandaj, Iran during 2004-2008. The results showed significant differences (p < /em>≤ 0.01) among the genotypes, in terms of the studied traits. The average total yield of fresh flowers was 2427.4 g/plant. The genotypes belonging to temperate and cool areas had lower flower yields than those originated from hot and dry areas. Flower yield showed a significant  and positive correlation with the crown height and diameter, the number of leaves, total green surface, and the number of flowers per plant (p ≤ 0.01). The results of stepwise regression showed that the flower weight and number positively, while the total green surface and flowering period negatively correlated with flower yield. The results of cluster analysis (CA) grouping were relatively consistent with segregation based on the flower yield and characteristics of genotypes origin areas. The results of principal component analysis (PCA) showed high consistency with the CA results, but the genotypic separation in PCA method was clearer. The overall results of this study along with CA and PCA analyzes showed considerable rich genetic variation among the genotypes in terms of phenological and morphological traits and the possibility of using this diversity in Iranian Damask rose breeding such as improving flower yield through direct and indirect selections (through flower yield components) or hybridization of genotypes with a greater genetic distance for the use of higher heterosis.

In this study, variation of beta-glucan content was assessed in 20 barley line and cultivars based on complete block design with three replications. Genetic diversity of these genotypes was also evaluated using ISSR markers. Beta-glucan extracted by an enzymatic method. Significant differences were found at the level of 1% among barley genotypes for beta-glucan content. The beta glucan content was variable from 7.21 to 12.48 and, the Yosef, E94B3 and E94B17 genotypes hold the highest content of the beta-glucan. ISSR primers with average polymorphism of 66.79%, genetic diversity of 0.25 and Shannon index of 0.37 were determined as efficient markers for studying genetic diversity. The barley lines and cultivars were assigned in two distinct groups according to their genetic pedigree. On the basis of non-parametric Kruskal-Wallis, Spearman correlation, and stepwise regression analysis, nine informative primers were detected explaining highest seed’s beta-glucan content variations ranging from 24.3 to 42.4 percent. The ISSR6 (700), the combination of ISSR1+ISSR4 (1400) and IS2+ ISSR2 (1400) primers were the most informative primers for the beta-glucan content. The informative markers provide possible functional and efficient marker based selection method and, screening the barley germplasms for the highest beta-glucan content.

To determine the traits affecting grain yield, 10 bread wheat genotypes including Morvarid and Kohdasht cultivars and Lines of N-87-4, N-87-9, N-86-6, N-86-8, N-80-19, N-86-5, N-85-5 and Line 17 were planted in two separate experiments including environmental conditions without heat stress in 15 December, and heat stress conditions of 10 February in Gonbad Kavous Agricultural Research Station during 2011-2012. Genotypes were compared in a randomized complete block design with three replications andwith combined analysis. Interaction of heat stress and genotypes were significant for grain yield, spike length, number of fertile spike. Genotypes and heat stress effect in all recorded traits were significant. In both conditions, grain yield had a positive and significant correlation with number of fertile spikes. Stepwise regression showed that the number of fertile spikes in normal conditions 99.8% and in heat stress 97.1% of grain yield changes were explained. The path analysis showed that the number of fertile spike had the most direct effect on grain yield in both conditions. The cluster analysis categorized genotypes into two group in normal conditions and three groups in heat stress conditions. Therefore, the number of fertile spikes can be used indirectly in the selection of genotypes with high yield in both heat and normal conditions.

To study phenotypic diversity and relationship among agronomical traits of 100 barley F3 generation families derived from cross between Badia × Komino barely cultivars, an experiment was conducted based on randomized complete block design with three replications at research field of Gonbad Kavous University during 2014-2015. Barley families had significantly high diversity in terms of awn length, spikelet no/spike. Grain yield was positive significantly correlated with total spike weight, seedlings number, plant height, awn length and biological yield and the highest correlation was observed between grain yield and total spike weight. In stepwise regression analysis, traits of seedlings number, days to heading, grain diameter, grains per spike, awn length had high contributed to grain yield. In path analysis the trait that had the most direct effect on yield was seedlings number. Barely families were classified into three groups regarding cluster analysis using Ward method and the third group was chosen as desirable one. On the whole, The most important factors influencing on yield increment of barley families was seedlings number and days to heading and these traits could be suitable choices to be used in barley breeding improvement programs.

This study was conducted to determine the relationship of RAPD and ISSR markers with virulence of 58 isolates of Cytospora chrysosperma (Pers.) Fr. on walnut seedlings using stepwise regression. The results of RAPD and ISSR tests showed that 10 out of 20 RAPD primers and 12 out of 20 ISSR primers had significant amount of appearance, polymorphism and repeatability among different isolates. Ten and twelve selected primers showed a high amount of polymorphic respectively 94.7% and 95.8% in different isolates. For further analysis the data of virulence trait, was considered as dependent variable and molecular data (0,1) were entered as independent variables in the regression models and the bands with high R2 in regression models were selected for further discussion. Five RAPD markers were related to virulence and totally explained 43.7% of variation of the trait. Out of them two markers showed positive relation and 3 of them showed negative relation with the virulence. The highest percentage of explained variance belonged to marker A7=1900 bp (R2=18.2%) and lowest was due to marker OP13=400 bp (R2=4.8%). Also five ISSR markers were related to virulence and totally explained 39% of variation of the trait. Out of them 3 markers showed positive relation and two of them showed negative relation with the virulence. The highest percentage of explained variance belonged to marker UBC864=350 bp (R2=11.6%) and lowest was due to marker UBC880=740 bp (R2=5.4%). Indentified markers could be used for marker assisted selection (MAS) and therefore to identify isolates.

To determine effective factors on grain yield under drought stress and non stress conditions at the end of the season، 15 bread wheat genotypes were examined as two separated experiments in Research Center of Faculty of Agriculture in Islamic Azad University، Tabriz Branch during 2012-2013. The cultivars were compared based on completely random block design with three replications. All studied traits were significant and there was frequent diversity among studied genotypes in the studied traits in both experimental conditions. The grain yield under non stress and stress conditions were 2. 8 and 2. 23 ha، respectively and drought stress had the most effect. The correlation coefficients among grain yield، biologic yield and harvest index were positive and significant in both experimental conditions and also grain yield under without stress showed a positive and significant correlation with number of spikelets per spike under stress conditions with spike length. According to stepwise regression under without stress conditions، number of spikelets per spike determined 40% of the grain yield changes. Also، in non stress conditions number of spikelets per spike and in stress condition spike length، plant height and pollination were most effective on grain yield and justified variation in grain yield and also genotype 14 showed higher yield relative to other genotypes in both experimental conditions.

To assess some traits of 20 barley genotypes, the experiment was done in a randomized complete block design with four replications in Agriculture and Natural Resources Research Station, of Khorramabad in 2011-2012 growing season. Grain yield and some other agronomic traits were measured. Differences between genotypes were compared in terms of plant height, biological yield, grain yield and hectoliter weight was significant. Genotypes of 1 and 15 had the highest grain yield. Simple correlation coefficients indicated that grain yield, biological yield, straw yield and spike weight had positive and significant correlation. Highest correlation was observed in grain yield and biological yield (r = 0.90**). The results of stepwise regression analysis showed biological yield, spike weight, flag leaf length, flag leaf area, spike length, awn length were the traits influencing on grain yield. Therefore, these attributes can be considered as the most important plant characteristics and they could be a suitable choice to improve the yield of barley genotypes breeding programs. Spike weight, biological yield had the highest direct effect on grain yield. Also, Genotypes of 1 and 15 had the highest yield. The traits such as weight, spike, flag leaf length, flag leaf area, awn length and head length which had high correlation with grain yield were effective on yield increment.

Relationships between different morphological traits were assessed on 75 tall fescue genotypes under moisture stress and non-stress conditions, using several multivariate statistical methods including regression analysis, path analysis and factor analysis during 2011 and 2012. Results showed that drought stress significantly affected all the studied traits except for days to ear emergence and plant height. There were significant differences among the genotypes for all the studied traits indicating a broad genetic diversity in the germplasm. Correlation coefficients of dry forage yield of the first and second cuts with most of the recorded traits under moisture stress and non-stress conditions were significant. The results of stepwise regression showed that crown diameter, days to pollination and the number of fertile spikes contributed in 63% of observed variation for forage production under non stress condition. Under stress condition, the number of fertile spikes, crown diameter and plant height contributed in 73% of the observed variation for forage production. Path analysis indicated that crown diameter and number of fertile spikes had the strongest direct effects on forage yield. Factor analysis for all of the traits revealed four factors under non-stress and stress conditions which justified 80 and 77 percent of the total variation, respectively. In factor number 1 traits such as forage yield, number of fertile spikes and crown diameter and in factor 2, days to ear emergence and pollination had the highest factor loads.

Genetic diversity of 30 varieties of advanced bread wheat (Triticum aestivum L.) was studied. A field experiment was conducted using a randomized complete block design with four replications at the Research Farm of Islamic Azad University, Miyaneh Branch in 2009. All agronomic practices were carried out by current procedure. Nineteen traits included days to germination, stem elongation, heading, physiologic maturity, ripening, awn length, leaf number main stem, flag leaf area, penultimate flag leaf area, plant height, peduncle length, number of spike/m2, grain numbers/spike, 1000 grains weight, biologic yield, harvest index, grain filling period, straw yield and grain yield were measured. Data were analyzed using multivariate techniques like principle components, stepwise regression and cluster approaches. Principal components analysis showed that first and second components could explain a 75.51% of total variations. Based on the characteristics in the first and second components, first components were considered for yield and the second one for phonology traits. Stepwise regression analysis for grain yield as a dependant variable and other characters as independents revealed that grain number/ spike, spike/ m2, plant height and main spike length could explain 98.7% of the variations. Finally, examined variety were grouped in three clusters and the third cluster contained 23.3% of total variations which presented higher grain yield than the first and second groups. According to the results obtained in this study, N-76-16 line could be introduced as a high-performance genotype and would have advantages in the breeding programs.

In other to evaluate genetic diversity, heritability and relationships between morphological and physiological traits with economic yield, an experiment was conducted on 17 chickpea genotypes for two years (2004-2005) in the research stations of Kermanshah, Lorestan and Ilam in the framework of completely randomized block design with 4 replications. Various statistical methods including: statistical parameters, genetic parameters, correlation between characters, multiple regression, path analysis and principal component analysis were calculated. Among the agronomic characters, grain yield and days number to % 50 maturities with CV of %41.35 and %4.22 indicated maximum and minimum coefficient of variation, respectively. Broadsense heritability ranged from %10.81 for primary branch numbers to %83.57 for plant height. Broadsense heritability for plant height, 100 seed weight, days number to %50 flowering and number of seed per plant were higher than those of the other characters. Stepwise regression for selection of traits related to economic yield indicated that seed number per plant and 100 seed weight explained 96.50 percent of total variation. The results of path analysis revealed that number of seed per plant and 100 seed weight with path coefficients of 0.947 and 0.262 had the highest direct effect on seed yield, respectively. Principal component analysis detected 2 components, which justified 69 percent of the total phenotypic variation of grain yield.