Evaluation of Elite Spring Wheat ( Triticum aestivum L . ) Genotypes for Yield and Yield Attributing Traits under Irrigated Condition

Thirty International Maize and Wheat Improvement Centre (CIMMYT) elite lines and Nepalese commercial wheat varieties were grown at Agriculture and Forestry University, Chitwan in Alpha-lattice design to identify high yielding genotypes, yield attributing parameters and correlations between them. Observations were taken for different morpho-physiological and yield attributing traits i.e., days to booting, heading, anthesis, maturity, flag leaf senescence, flag leaf duration, grain filling duration, plant height, spike length, number of grains per spike, thousand kernel weight, hectoliter weight, grain yield and biomass yield. Significant genotypic differences were observed for all the traits studied indicating considerable amount of variation among genotypes for each character. The mean grain yield was 2148 kg/ha and it ranged from 1000 to 3425 kg/ha. BLOUK#1/4/WHEAR/KUKUNA/3/C80.1/3*BATAVIA//2*WBLL1/5/MUNAL #1 (35 ESWYT138) was the highest grain yielding genotype among all followed by CHIBIA//PRLII/CM65531/3/FISCAL/4/DANPHE#1/5/CHIBIA//PRLII/CM65531/3/SKAUZ/BAV92 (ESWYT 141), Gautam, Vijay and CHYAK1*2/3/HUW234+LR34/PRINIA//PFAU/WEAVER (ESWYT129). Grain yield had significant strong positive correlation with grain filling duration (0.685), plant height (0.606), thousand kernel weight (0.675), biomass yield (0.892) and hectoliter weight (0.586). Four clusters were formed by cluster analysis and genotypes were grouped in a particular cluster on the basis of similarity of morpho-physiological traits. So, these genotypes may be exploited for their direct release or as parents in hybridization programmes to develop high yielding wheat varieties.


Introduction
Wheat (Triticum aestivum L.) is considered as one of the major cereal crops which belongs to the grass family (Class Liliopsida, Family Poaceae and Tribe Triticeae) (Shewry, 2009).It produces large edible grains which acts as a source of about one half of human food and a major portion of nutrient requirement.Wheat also known as king of cereals is a direct source of food for human beings.It is the most important cereal crop of the world providing staple food for around 35% of the world population and about 36% of the world's production is in Asia (FAOSTAT, 2014).
The primary objective of the spring bread wheat improvement program at International Maize and Wheat Improvement Centre (CIMMYT) is to develop wheat germplasm that is widely adapted, higher yielding, high quality, disease resistant, and stress tolerant.International distribution and testing of CIMMYT-derived advanced wheat breeding lines across diverse environments worldwide with a focus on CIMMYT has characterized the world's diverse wheat production zones into several megaenvironments, and its wheat improvement priorities are targeted accordingly (Rajaram et al., 1995;Braun et al., 2010).The importance of international wheat improvement efforts for fulfilling wheat global demands by developing improved varieties was underlined by Dr. Norman E. Borlaug in the early 1960s (Borlaug, 1968).Historically, CIMMYT's bread wheat breeding program has produced outstanding genotypes with significantly increased grain yield potential (Rajaram, 2005).'Kalyansona' and 'Sonalika' are considered wheat mega-varieties of the "Green Revolution" era (Rajaram et al., 1995).Although Research Article numerous CIMMYT-derived varieties have subsequently been released and grown, hallmark post-green revolution mega-varieties developed from 'Veery', 'Kauz', and Attila crosses were widely grown in many developing countries under different names.Previous studies have documented the wide adaptation of outstanding bread wheat genotypes developed at CIMMYT (Trethowan et al., 2001;Singh, et al., 2007).In addition, outstanding CIMMYT-derived bread wheat lines have been widely used in crossing programs across the developing world (Braun et al., 1996) and have greatly enriched the genetic diversity of wheat cultivars in many countries (Smale et al., 2002).
The CIMMYT-derived high yielding wheat varieties have also exhibited resistance or tolerance to serious biotic and abiotic stresses.For example, targeted breeding for the rust resistance have achieved success in incorporating high levels of disease resistance into CIMMYT-derived high yielding wheat genotypes ( Van Ginkel and Rajaram, 1993).Use of synthetic hexaploids derived from crosses between tetraploid durum wheat (Triticum turgidum L.) and diploid Aegilops tauschii Coss. in the 1990s resulted in several outstanding wheat lines that combine high yield with disease resistance (Villareal et al., 1994) and tolerance to abiotic stresses ( Trethowan et al., 2001).The world food demand is increasing continuously, thus it is now a compulsion to develop wheat varieties having higher yield potential, higher tolerance to warmer temperatures, and have improved water use efficiency and drought tolerance.Wheat yield stagnation has been reported in the past decade from South Asia (Mehlka et al., 2000) and Europe (Petersen et al., 2010).Each year since 1981, CIMMYT's spring bread wheat breeding program has been distributing the Elite Spring Wheat Yield Trial (ESWYT), which includes new elite lines targeted for irrigated environments worldwide.
Adoption of improved varieties has potential to increase the production and productivity of wheat by at least two folds.Therefore, there is need to analyze and evaluate the advance lines developed by National Agriculture Research System, CIMMYT with wider genetic base to develop cultivars suitable for our environments.Hence, this study was conducted with the objective to study genotypic performance of wheat lines developed by Nepal Agriculture Research Council and CIMMYT on phenological, agromorphological, grain yield and its components and others traits and to study relationship among various yield attributing traits and economic yield.

Methodology
The experiment was conducted at the research farm of Agriculture and Forestry University, Rampur, Chitwan, Nepal, from November 2015 to June 2016.The research site was located at 27.64768 0 N latitude and 84.34750 0 E longitude and at an altitude of 171 meters above sea level.The site contained sandy loam soil with acidic reaction.Thirty bread wheat genotypes were used as plant material in this study (Table 1).They were obtained from the Agriculture Botany Division, Nepal Agriculture Research Coucil, Khumaltar, Nepal which included 23 elite lines selected from 35 th Elite Spring Wheat Yield Trial (ESWYT), 5 biofortified harvest plus lines from 5 th Harvest Plus Yield Trial (HPYT) developed from CIMMYT, Mexico, and 2 Nepalese commercial cultivars, namely Vijay and Gautam.The experiment was conducted in Alphalattice design with thirty wheat genotypes as treatments with three replications.Each replication consisted of 5 blocks and six plots were formed in each block.Each plot was 2 m in length and 2 m in width.Each plot consisted of 8 rows with a spacing of 25 cm between rows and continuous sowing was done in each row.The planting was done in 4 th December 2015.The chemical fertilizers were applied at the rate of 120:60:60 kg NPK per hectare.First irrigation was done at the crown root initiation (CRI) stage (Zadoks' growth stage Z1.3, Z2.1) second at the time of booting stage (Zadoks' growth stage) and third at grain filling stage.
Observations were recorded for days to booting, days to heading, days to anthesis, days to maturity, days to flag leaf senescence, flag leaf duration, grain filling duration, plant height, spike length, grains per spike, thousand kernel weight, biomass yield, grain yield and hectoliter weight.Data entry and processing was carried out using Microsoft Office Excel 2007.Analysis of variance, mean comparison between genotypes based on LSD by using R Studio software package.Pearson's correlation analysis was performed using SPSS v.16.

Days to Booting, Heading and Anthesis
Analysis of variance showed that there was highly significant difference between the wheat genotypes for booting, heading and anthesis days (Table 2).The mean number of booting days for thirty wheat genotypes was 75 days (Table 4).BAJ #1 booted earliest in 70 days followed by NELOKI/3/IWA 8600211//2*PBW343*2/KUKUNA (72 days), KACHU#1 (72 days) and Vijay (73 days) while KACHU #1 took longest days to boot i.e. 80 days.Majority of the genotypes (70%) booted in the range of 73 to 77 days.

Flag Leaf Senescence and Duration
There was highly significant variation among genotypes for flag leaf senescence and flag leaf duration as analyzed from Analysis of Variance (Table 2).The mean number of days for flag leaf senescence was 107 days and flag leaf duration was 36 days (

Days to Maturity and Grain Filling Duration
For days to maturity and grain filling duration, highly significant difference was observed among the genotypes (Table 2).The average number of days to maturity was 115 days (

Spike Length
Analysis of variance revealed highly significant difference among genotypes for spike length (Table 3).The average spike length was 9.8 cm (Table 3).It varied from 8.1 cm to 12.4 cm with the maximum spike length observed on Gautam and minimum on BAJ #1/KISKADEE #1 (ESWYT 139).Twenty two genotypes had spike length between 8 to 10 cm and eight genotypes had above 10 cm.

Number of Grains per Spike
There was highly significant variation among genotypes for number of grains per spike (  23) had between 40 to 50, three genotypes had above 50 and four genotypes had below 40 grains per spike.

Correlation Analysis
Pearson's correlation analysis showed significant correlations among the variables studied (Table 4).Days to heading showed significant positive correlation with days to maturity (0.40 * ) but negatively correlated with grain filling duration (-0.53 ** ).Days to maturity was positively correlated with flag leaf duration (0.64 ** ) and hectoliter weight (0.52 ** ) at high level of significance and positively correlated with grain filling duration (0.46 * ), spike length (0.43 * ) and biomass yield (0.38 * ).Flag leaf duration was positively correlated with grain yield (0.35) and hectoliter weight (0.363 * ).Grain filling duration had highly significant positive correlation with plant height (0.63 ** ), thousand kernel weight (0.60 ** ), grain yield (0.69 ** ), biomass yield (0.73 ** ) and hectoliter weight (0.71 ** ).Plant height was positively correlated with spike length (0.45 * ), thousand kernel weight (0.40 * ), grain yield (0.61 ** ), biomass yield (0.61 ** ) and hectoliter weight (0.56 ** ).Spike length and number of grains per spike were positively correlated (0.33).Thousand kernel weight showed highly significant positive correlation with grain yield (0.68 ** ), biomass yield (0.59 ** ) and hectoliter weight (0.497 ** ).There was highly significant positive correlation of grain yield with biomass yield (0.89 ** ) and hectoliter weight (0.59 ** ).Biomass yield and hectoliter weight were positively correlated (0.75 ** ).Production of wheat yield fluctuates widely as a result of its interaction with environment because grain yield is a complicated quantitative parameter and is the product of several contributing factors affecting grain yield directly or indirectly.Wheat production can be increased through development of productive varieties which better adapt to various agro-climatic conditions and also resist all types of stresses.Selection for grain yield improvement can only be effective if sufficient genetic variability is present in the breeding material (Ali et al., 2008).Genotypic and phenotypic correlations are important breeding parameters used for determining the degree of association of various yield contributing parameters with grain yield (Ali et al., 2008).Many earlier researchers studied phenotypic correlations of various grain yield components with wheat grain yield for its genotypic improvement (Shahid et al., 2002;Aycicek and Yildirim, 2006).
Grain yield of wheat is a complex trait and is affected by various components like; number of tillers/m 2 , number of grains per spike, 1000 grain weight, and plant height and spike length.There were significant differences among the genotypes for all the traits studied which are in agreement with Sharma (1994); Kamat (1996); Ginkel et al., (1998); Dwivedi et al., (2002); Sinha et al., (2006); Kamboj (2007) and Baloch, et al., (2013) who reported high variability for different traits in wheat.Thus, it is implied that there was reasonably sufficient variability in the research material, which provides ample scope for selecting superior and desired genotypes by the plant breeder for further improvement.
Successful breeding of high yielding varieties depends on the yield contributing morphological traits and choosing small number of important traits having positive correlation.There were significant positive correlations among different variables and yield components.These results are in agreement with Akram et al., (2008) who reported positive correlation between grain yield and 1000grain weight, while Kashif and Khaliq (2004) also found that yield components like tillers per plant had significantly contributed towards grain yield development.They also noted that number of heads per m 2 , grains/spike and 1000 grain weight were main contributors to grain yield in wheat.
It was also reported that the grain yield per plant showed significantly positive association with productive tillers per plant, plant height, 1000-grain weight and spike length at both genotypic and phenotypic levels (Aycicek and Yildirim, 2006).The present study suggests that high yielding varieties of wheat may be selected by the indirect selection through grain filling duration, plant height, thousand kernel weight, biological weight and the hectoliter weight.
The correlation results were also in agreement with (Ojha, 2012) who reported a significant positive correlation between grain yield and thousand seeds weight, number of grains per spike, flag leaf duration, grain filling duration and plant height.Similar findings were reported by Thapa et al. (2009)

Table 1 :
List of wheat genotypes grown for the field experiment, 2015/2016

Table 2 :
Mean values of Days to booting (DB), Days to heading (DH), Days to anthesis (DA), Days to Flag leaf senescence (FLS), Flag leaf duration (FLD), Days to maturity (DM) and Grain filling duration (GFD) of thirty wheat genotypes under study *: significant in 5% level, **: significant in 1% level

Table 4 :
Pearson's correlation coefficient among different traits of thirty wheat genotypes under study Values are significantly different at 5% level of significance (*) and highly significantly different at 1% level of significance (**).DH= Days to heading, DM= Days to maturity, FLD= Flag leaf duration, GFD= Grain filling duration, PH= Plant height, SL= Spike length, NGPS= Grains per spike, TKW= Thousand kernel weight, GY= Grain yield, BY= Biomass yield, Kg/hL= Hectoliter weight also.