sequential path analysis

Soybean seed contains about 20% oil and 40% protein and is considered as a strategic oilseed plant. Identification of the relationship between morphological traits and seed yield and improving the traits that have strong associtation with seed yield can increase the efficiency of the soybean breeding programs for seed yield improvement.

To determine the suitable indirect selection index for seed yield in soybean, the important morphological traits were evaluated in 10 soybean cultivars in randomized complete block design with three replications and multivariate statistical methods in research farm of Sari University of Agriculture Sciences and Natural Resources, Sari, Iran, in two growing seasons (2020 and 2021).

The results showed that there was significant differences between soybean cultivars for the morphological traits which indicates considerable variation among Iranian soybean cultivars. The results also showed that cv. Telar with the highest number of branches, number of pods plant-1, number of seeds pod-1 and pods weight plant-1 had the highest seed yield (5400 kg.ha-1) in the 2020 and cv. Katol with the tallest plant height, the highest number of branches, pods weight plant-1 and the 100-seed weight had the highest seed yield in 2020 and 2021 (5200 and 7688 kg.ha-1, respectively). The results of multivariate analysis showed that among the studied traits, pods weight plant-1 and plant height directly, the number of pods plant-1 with a direct effect on the pods weight plant-1 and also the 100 seed weight with a direct effect on plant height had highly positive effects on seed yield in soybean. Furthermore, the number of pods plant-1 showed negative relationship with 100 seed weight. Moreover, the results of cluster analysis showed that cv. Telar and cv. Parto were distinguished from other cultivars for short plant height and high number of pods plant-1, cv. Katol for tall plant height and high 100-seed weight and cv. Tapur for high number of seeds pod-1.

Since pods weight plant-1, plant height, number of pods plant-1 and 100 seed weight showed high positive direct effects on seed yield, therefore, cv. Prato and cv. Telar with the highest number of pods plant-1 and cv. Katol with the tallest plant height and the highest 100 seed weight can be considered for seed yield improvement in soybean breeding programs.

Study on relationships between yield and other agronomic traits will improve the efficiency of a breeding program with appropriate selection criteria. In this regard, 24 new sunflower hybrids along with Golsa cultivar were evaluated in a simple lattice design with two replications in agriculture research station of Gorgan during 2020 cropping season. The results indicated that the highest coefficient correlation was obtained between head diameter and thousand seed weight with seed yield. Sequential stepwise multiple regression analysis was performed to organize the predictor variables into first, second and third order paths based on their respective contributions to the total variation of yield and minimum collinearity. Based on the variance inflation factor and magnitude of direct effects, seed number per plant, thousand seed weight and stem diameter were considered as first order variables and accounted for 70 percent of total variation of seed yield. The t-test of significance, using standard error values, obtained through bootstrap resampling, indicating that all direct effects were significant. Generally, the results indicated three traits of seed number per plant, thousand seed weight and stem diameter could be considered as selection criterion in selecting for increased yield in sunflower. Also, the results indicated that among studied genotypes, genotypes No. 2, 4, 5, 10, 11, 19 and 22 were recognized as superior genotypes regarding seed yield and traits related to yield.

Breeding new crop cultivars with efficient root systems carries great potential to enhance resource use efficiency, plant adaptation to unstable climates and improve yields. Current study was conducted to investigate the relationship between root characteristics with yield and yield components in 24 lines and cultivar of bread wheat using complete randomized block design with three replications in rainfed conditions of research farm of the University of Zanjan in 2017-18 and 2018-19 growing seasons. The results of combined analysis of variance showed the difference between year and high diversity between genotypes measured for most traits. According to the results of the study of genetic parameters, the highest heritability was related to the number of grains per spike (70.328%) and the heritability of the most root traits was low. There was a negative correlation between yields with the most root traits but root diameter. The results of sequential path analysis showed that in the first stage of chain 1000-grain weight, number of spikes per square meter and number of seeds per spike affected grain yield, and in the second stage, root dry weight and diameter greater than 25cm deep and root volume to a depth of 25cm with effects on 1000-grain weight, root volume greater than 25cm deep and root dry weight to a depth of 25cm with effects on spike number per square meter and root volume to a depth of 25cm with effects on seed number per spike, they Indirectly affected grain yield. The results of factor analysis led to the identification of four factors that explained 82.45% of the differences between the data. Based on the results of cluster analysis, the studied genotypes were divided into three groups. The cultivars and lines in the second group had the highest yield with the highest root volume, diameter, dry weight, surface and length to a depth of 25cm.

In arid and semi-arid regions of the world including Iran, soil salinity is one of the major abiotic stresses. One of the ways to achieve high performance in these areas is using salt tolerant varieties. Also, study on relationships between yield and its components will improve the efficiency of a breeding program with appropriate selection criteria. In this study, 110 bread wheat genotypes were evaluated in two conditions (non-stress and saline stress) at the research field of the National Salinity Research Center (NSRC). The salinity of water used in irrigation in saline and non-stress conditions was 10 and 2 dS.m-1 respectively. In this study was used of stress tolerance index (STI) as the best indicators for evaluating of tolerant to salinity stress of bread wheat genotypes. Based on stress tolerance index (STI)and seed yield in non-stress and saline stress conditions, the linesSalt18, Salt19, Salt20, Salt21, Salt22, Salt23, Salt24, Salt25, Salt26, Salt27, Salt28, Salt29, Salt30, and varieties Arg, Bam, Rushan, Sorkhtokhm, BumiYazd, Kavir, Moghan 1, Sardari, Sharyar, Shirazhad had a high yield in the non-stress and saline stress conditions and these genotypes were selected as the most tolerant genotypes to salinity.The highest grain yield under non-stress and saline stress conditions was produced by Salt29 line (178.13 gr) and Salt24 line (164.33 gr), respectively which had more grain yield than control cultivars (Arg, Bam, Rushan, Sorkhtokhm, Bumi Yazd and Karchia). Also, based on the results of sequential path analysis, kernel weight per spike and number of fertile tillers in non-stress conditions and spike weight, number of fertile tillers, days to headingand peduncle weightin saline stress conditions were selected as first order variables.Therefore, it seems that these traits could be used as a suitable criterion in wheat breeding programs for increased seed yield in both non-stress and salinity stress conditions.

To evaluate the relationship between seed yield and its components in peanut (Arachis hypogaea L.), 78 genotypes of peanut were grown in a randomized complete block design with three replications at Takatoo research station, Sari, Iran, in 2016 and 17 plant traits related to seed yield were measured. Analysis of variance showed that there were significant differences in all traits (except for seed width), that indicated a considerable variation between peanut genotypes. Based on the results of multiple stepwise regression analysis, first, second and third ranked variables were evaluated by considering the contribution in seed yield variation and minimum co-liner and the seed length and number of pod.plant-1 were selected as first ranked variables (76% of variation of seed yield). Results showed that the seed length and number of pod.plant-1 had a negative (non significant) relationship with seed yield. The results of sequential path analysis showed that the direct effect of number of pod.plant-1 (r = 0.815**) and seed length (r = -0.810**), were the most effective component in seed yield. Based on the correlation analysis result, number of pod.plant-1 may be used as selection index to promote the seed yield in peanut.

Coriander is mainly cultivated and widely distributed for the seeds. Therefore, development cultivar with high seed yield is important in coriander. On other hands, seed yield is a complex quantitative trait, considerably affected by environment and usually has a low heritability. Therefore, Study on relationships between yield and its components will improve the efficiency of a breeding program with appropriate selection criteria. The objectives of this research were to analyze the correlation between seed yield and related traits in coriander and by applyusing sequential path analysis and heritability estimates to identifying effective traits for which may be useful in breeding higher-yieldingimprove coriander genotypes. Plant materials including 36 genotypes of diallel crosses progenies of six coriander landrace and theirF1 and F2 generations were evaluated in randomized complete block design with three replications. The phonological, morphological characteristics and yield and its components including days to flowering, days to end of flowering, days to ripening, leaf number, branch number per plant, umbel number per plant, fertile umbel number per plant, seed number per plant, thousand seed weight, seed weight per plant (seed yield) and chlorophyll content were measured. Diallel analysis through Griffing method, correlation analysis, stepwise regression analysis and sequential path analysis was performed on the data. Results of genetic analysis of variance showed significant general and specific combining abilities for all traits that reveals the importance of both additive and non additive gene effect in controlling these traits. Also, results showed that the highest coefficient correlation was obtained between fertile umbel number per plant (r=0.67**) and thousand seed weight (r=0.66**) with seed yield. Sequential stepwise multiple regression analysis was performed to organize the predictor variables into first and second order paths based on their respective contributions to the total variation of yield and minimum collinearity. Based on the variance inflation factor and magnitude of direct effects, fertile umbel number per plant (r=0.45**), days to flowering (r=-0.46**), thousand seed weight (r=0.31**) and seed number per plant (r=0.30**) were considered as first order variables and accounted for 86 percent of total variation of yield. The t-test of significance, using standard error values, indicating that all direct effects were significant. Number of fertile umbels had the largest direct effect (0.45) on seed weight and also number of fertile umbels had the largest indirect effect (0.40) on seed weight through thousand seed weight. The results indicated that three traits including fertile umbel number per plant, thousand seed weight and seed number per plant considering the positive correlation and direct effect with seed yield and having additive genetic control and high narrow-sense heritability, can be used as a suitable criterion in selecting for increased seed yield in breeding programs of coriander in different generations of coriander under field conditions. Also, considering the negative correlation and direct effect of day to flowering with seed yield and having additive genetic control and high narrow-sense heritability, early maturity can be considered as an independent selection index for breeding of different varieties of coriander