Nurry Gummov,Msut Ksr,Byhn Akin,Must Ckmk,Zr Mrt, Syi Tnr,Irn Ozturk,Ali Topl,Slmi Yzr,Alxy Morounov,*

aInternational Maize and Wheat Improvement Center(CIMMYT),Emek,Ankara,Turkey

bInternational Center for Agricultural Research in the Dry Areas(ICARDA),Emek,Ankara,Turkey

cTransitional Zone Agricultural Research Institute,Tepebası,Eskişehir,Turkey

dField Crops Central Research Institute,Ankara,Turkey

eBahri DağdaşInternational Agricultural Research Institute,Konya,Turkey

fTrakya Agricultural Research Institute,Edirne,Turkey

gSelçuk University,Faculty of Agriculture,Field Crops,Konya,Turkey

Genetic gains in wheat in Turkey:Winter wheat for irrigated conditions

Nurberdy Gummadova,Mesut Keserb,Beyhan Akina,Mustafa Cakmakc,Zafer Mertd, Seyfi Tanere,Irfan Ozturkf,Ali Topalg,Selami Yazard,Alexey Morgounova,*

aInternational Maize and Wheat Improvement Center(CIMMYT),Emek,Ankara,Turkey

bInternational Center for Agricultural Research in the Dry Areas(ICARDA),Emek,Ankara,Turkey

cTransitional Zone Agricultural Research Institute,Tepebası,Eskişehir,Turkey

dField Crops Central Research Institute,Ankara,Turkey

eBahri DağdaşInternational Agricultural Research Institute,Konya,Turkey

fTrakya Agricultural Research Institute,Edirne,Turkey

gSelçuk University,Faculty of Agriculture,Field Crops,Konya,Turkey

A R T I C L E I N F O

Article history:

Accepted 30 September 2015

Available online 14 October 2015

Bread wheat Yield potential Reduced plant height Irrigated environment

The study estimated genetic gain for yield and other traits in winter wheat released for irrigated environments in Turkey from 1963 to 2004.Yield trials including 14 varieties were grown in 16 environments from 2008 to 2012 in provinces of Konya,Eskişehir,Ankara,and Edirne.The highest yields were achieved by recent varieties Kinaci-97(5.48 t ha-1), Cetinel-2000(5.39 t ha-1),Alpu-2001(5.44 t ha-1),Ahmetaga(5.35 t ha-1),and Ekiz-2004 (5.42 t ha-1)compared to older varieties Yektay-406(4.17 t ha-1)and Bezostaya-1(4.27 t ha-1) released in the 1960s.The progress reached in grain yield in 20 years was 1.16 t ha-1or 58 kg ha-1(1.37%)per year.This gain was mainly achieved through shorter plant height and increased harvest index.There was no clear tendency of changes in specific yield components demonstrating that new high-yielding varieties may have different ways to reach their yield potentials.The yield gains were accompanied by improved stripe rust and leaf rust resistances primarily based on adult plant resistance genes.The grain quality of the new varieties did not deteriorate over time although most of them were inferior to the bread-making quality check Bezostaya-1,a feature that may require attention in future breeding.

©2015 Crop Science Society of China and Institute of Crop Science,CAAS.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

1.Introduction

Wheat is a leading field crop throughout the world,including Turkey.Turkey has a suitable,but diverse,ecology for wheat production(Fig.1)and is part of the center of origin for wheat. Therefore,Turkey has advantages for the development of productive high-quality varieties of wheat,a nationally strategic crop.Two hundred and one bread wheat varieties were included in the 2014 official Turkey registration list[1]. Wheat production in Turkey,which was about 2.5 millionmetric tons in the 1930s,reached 10 million tons in 1967,and 20.6 million tons in 2009.The increase in production was primarily due to the increased planting areas from the 1930s to 1960s.The grain yield per unit area was 920 kg ha-1in 1930 and reached 1250 kg ha-1in 1967.The increase in planting areas between 1967 and 2010 was only 1.0%,but the increase in grain yield was 104.8%[2].This yield increase was realized by significant contributions in both genetic value of the varieties used and improved agronomy,irrigation and fertilization.The yield increase in Turkey depended on the genetic structure ofcultivated varieties and was respectively 50%under irrigated conditions and 20-30%under rainfed conditions[3].

Fig.1–Wheat production regions of Turkey and our experimental sites used in the study(data source wheat area and irrigation share:www.tuik.gov.tr for 2014;author's estimates of winter and spring wheat shares).Marmara:60%winter wheat and 40%fallplanted spring wheat,lowland＜400 m.a.s.l.,high rainfallenvironment,0.83 Mha ofwheat;Black Sea:fallplanted spring wheat,mountain valleys＜1000 m.a.s.l.,high rainfall,0.79 Mha;Central Anatolia:winter wheat at 800–1200 m.a.s.l., low rainfall,20%of area irrigated,2.75 Mha;Eastern Anatolia:winter wheat＞1200 m.a.s.l.,low rainfal,cold winter,35% irrigated,0.71 Mha;Southeast Anatolia:facultative and spring wheat,primarily durum,＜800 m.a.s.l.;low raifall,35%irrigated, 1.27 Mha;Mediterranean:fall planted spring wheat,high rainfall or irrigated(40%),＜600 m.a.s.l.,0.80 Mha;Aegean:fall planted spring wheat,high rainfall or irrigated(30%),＜600 m.a.s.l.,0.67 Mha.Experimental sites:1,Ankara;2,Konya;3, Eskişehir;4,Edirne.

In recent years wheat productivity worldwide has increased substantially.Many studies have been conducted to analyze such increases.Cox et al.[4]studied 35 hard red winter wheat varieties in three different locations in order to determine the genetic progress in wheat yields in the USA state of Kansas between 1874 and 1987.They estimated a 16.2 kg ha-1annual increase with associated increases in test weight and 1000-kernel weight while biomass remained largely unchanged.A similar study was conducted over 4 years(Berzonsky and Lafever[5])on winter bread wheat varieties developed between 1871 and 1987 in the state of Ohio,USA.The trend was for reduced height,better lodging tolerance and earlier development.Zhou et al.[6]carried out trials on 47 winter bread wheat varieties developed between 1960 and 2000 in the North China Winter Wheat region and reported progress of 32-72 kg ha-1(0.48-1.23%)per year in productivity depending on the province.The gain was attributed to successful utilization of Rht genes and the 1B.1R translocation.In a study conducted with facultative bread wheat varieties developed in Henan province of China during 1981 to 2008[7],increased productivity was estimated at 56.3 kg ha-1(0.6%)annually and was largely attributed to increased 1000-kernel weight.Austin et al.[8]conducted a 3-year trialon 13 winter bread wheatvarieties representing very old,old,less old and modern groups.It was observed that modern varieties produced 59%more grain yield than the very old varieties,14%more spikes per meter square,and 30%more grains per spike.New varieties headed 6 days earlier than old ones and produced more biomass.Miri[9]conducted a study on 15 varieties in order to understand the morpho-physiological properties of wheat varieties registered in Iran between 1940 and 2000,and to determine the relationship of these changes with grain yield.As a result of this analysis,he reported that grain yield increases over the last 60 years were statistically significant(r=0.78,P＜0.01).

A limited number of studies on genetic progress have been conducted in Turkey to date on wheat.From trials conducted over 5 years in Central Anatolia on 13 bread wheat varieties developed between 1933 and 1991 Avcin et al.[10]estimated a 16.1 kg ha-1genetic gain per annum in grain yield during the period.The same researchers estimated a 10.3 kg ha-1per year genetic gain in durum wheat in the same region[11].Kuşcu[12] evaluated a chronological set of 16(spring bread wheat) varieties released after 1976 using two nitrogen application levels in theÇukurova region during the 2002/2003 and 2003/ 2004 wheat growing seasons.The average rate of yield increase of 0.64%per year resulted from increased harvest index associated with reduced height and more grains per spike. From a study carried out with 16 bread wheat varieties in the Mediterranean region over two years Sener et al.[13]concluded that genetic progress was insufficient and should be supported by better technologies and improved agronomy.

Determination of the factors that increase or restrict wheat productivity is important for developing future improvement strategies.Various studies on increases in wheat productivity attributed yield gains to a number of parameters.Somereported that increased in grain yield came from increases in harvest index[9,12,14].Others suggested that total biomass rather than harvest index was the main factor contributing to genetic progress[15].Other studies indicated that the component most affecting wheat productivity was grain number per spike[11],grain number per square meter[16].However, the majority of studies indicated that productivity increases can be obtained by increasing harvest index without decreasing biomass.

The objective ofthe current study was to documentgenetic gains in grain yield and associated changes in agronomic traits in Turkish irrigated winter wheat to assist in developing future breeding strategies.

2.Materials and methods

2.1.Varieties,experimentaldesign and traits

The study was conducted in Agricultural Research Institutes in four provinces(Ankara,Konya,Eskişehir,and Edirne) during 5 seasons from 2008 to 2012.Fourteen registered winter bread wheat varieties developed for irrigated conditions and released from 1963 to 2004 were used in the study (Table 1).The criteria for variety selection were commercial production under irrigated conditions in Turkey and contribution to overall production.The trials were conducted in a randomized block design,with 4 replications in 2008 and 2009, with 2 replications in Konya in 2012,and 3 replications in all other sites×years(Table 2).Plots were 6 rows of 7.0 m×1.2 m. The distance between rows was 20 cmand 450 seeds were used per square meter.One hundred kg of P and 39 kg of N were applied per hectare at the time of planting.An additional 50 kg ha-1was given at tillering.In most locations(except Ankara in 2008 and Edirne),50 mm of irrigation was applied once or twice.The herbicide 2,4-D was applied at the rate of 1.5 L ha-1before stem elongation for weed control.Harvesting was conducted at maturity with a combine plot harvester leaving a 1.0 m edges at the beginning and ends of plots(i.e.a harvested plot size of 5.0 m×1.2 m).

Data were recorded for the following traits:plant height, days to heading,biomass,harvest index,spikes m-2,grains per spike,1000-kernel weight,test weight,protein content, gluten content,SDS sedimentation,disease reactions and grain yield.Not all data were recorded in allyears,the number of observation used for each trait is listed in Table 3.Yield components were evaluated using 10 random plants from each plot.Protein and dry gluten content were evaluated using near infra-red(NIR)spectroscopy.SDS sedimentation was evaluated by the micro-method with 1 g of flour.Field reactions to yellow rust,leaf rust,and stem rust were based on severity.Seedling leaf rust and yellow rust tests were conducted in a greenhouse using bulk urediniospore collections from the field.

Growth habit was evaluated by planting non-vernalized seeds in late April when the average minimum daily temperature exceeded 10°C.Genotypes that remained at the tillering stage when those with spring habit had headed were classified as winter types.The presence of the 1B.1R translocation was predicted by association with Glu-B3j marker[17]. Molecular marker data for Rht-B1,Lr and Yr genes were provided by the CIMMYT Biotechnology group in Mexico.

2.2.Climate and weather conditions at experimentalsites

The Ankara,Konya,and Eskişehir provinces in which the trials were conducted are located on the Central Anatolian Plateau(Fig.1).The summers in this territory are relatively hot and winters are cold.The coldest month is January with an average temperature of-0.7°C.In the hot month of July the average temperature is 22°C.The annual average temperature is 10.8°C.The annual average precipitation is415 mm and the rain falls mainly in winter and spring.Edirne province is in the European Thrace region of Turkey.This territory is not as cold in winter or as dry in summer as Central Anatolia.The average temperatures in January and July are 4.9°C and 23.7°C,respectively.The annual average temperature is 14.0°C.The average annual winter-dominant precipitation is 595 mm.There were no significant differences in weather parameters between January and May in all locations during the course of the study(Table 2).The lowest average temperature for January of-3.9°C was at Ankara in 2008.However,no winter-killwas recorded in any trial.There was not much difference in average spring temperatures at the locations,either long-term and during the study period. Total precipitation in Konya,Eskişehir,and Ankara exceeded the long-term average in 2009 and 2011,and was below the long-term average in 2008,2010(except Konya),and 2012. Edirne received precipitation below the long-term average in 2011 and above the long-term average in 2012.Grain yields were high in locations with high precipitation.The Konya and Eskişehir sites were relatively similar in precipitation and grain yield.The highest precipitation and grain yield were obtained in Edirne province in 2012.

Table 1–Historical set of wheat varieties included in genetic gain experiments in 2008 through 2012.

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2.3.Data analysis

Data were analyzed with the“JMP”statistics package according to a randomized block design.The significance of differences of means was checked by LSD test.A regression analysis was carried out in order to determine the genetic progress over time with years as the independent variable(x) and productivity traits as dependent variables(y).The average yield,regression coefficient(b),and total squared deviation from regressions were used to determine the stability of varieties in this study.Correlations between grain yield and other traits were calculated using Microsoft Excel software.

3.Results

3.1.Grain yield

The average grain yield for individual experiments varied from below 3 t ha-1(Ankara,2008 and Konya,2012)to above 6 t ha-1(Eskişehir,2009,Konya,2011,Eskişehir,2011,and Edirne,2012)(Table 2).All trials with the exception of Ankara 2008 and 2012 recorded significant differences in grain yield. Variation in yield and other traits across locations and years was sufficient for detailed evaluation of the historical variety set.The lowest average yields were obtained for the three oldest varieties:Yektay-406(4.17 t ha-1released in 1963), Bezostaya-1(4.27 t ha-1released in 1968),and Kirkpinar (4.61 t ha-1released in 1979)(Table 3).Varieties released after 2000 had the highest yield as a group,clearly demonstrating genetic gains.According to the regression analysis between grain yield and release years,increases in grain yield were statistically significant(R2=0.657)and the increase was 27 kg ha-1per year from 1963(Fig.2-A).This annual increase compared to the yield of Yektay-406(4.17 t ha-1)constitutes a 0.65%rate of genetic gain.The alternative calculation approach was to compare the average yields of two varieties(Ahmetaga and Ekiz-2004)released in 2004(5.38 t ha-1)with the average yield of Yektay-406 and Bezostaya-1(4.22 t ha-1) released in the 1960s.The annual rate of progress in grain yield over 20 years was 1.16 t ha-1or 58 kg ha-1per year or 1.37%.However,if the two oldest varieties are removed from the analysis,yield gain although positive is non-significant (Fig.2-B).The visible decline in rate of genetic gain among varieties released after 1995 is concerning.

Fig.2–Regression ofyield and other traits on release year.(A)Yields for allvarieties,t ha-1;(B)yields for varieties released after 1979,t ha-1;(C)harvest indices for all varieties;(D)harvest indices for varieties released after 1979.**P=0.01,***P=0.001.

3.2.Yield components

It is important to understand the main traits contributing to genetic gains demonstrated in this study.Regression analysis of the main agronomic traits over the year of variety release did not find significant changes in days to heading,total biomass,and 1000-kernel weight.The number of spikes per unit area and number of grains per spike increased slightly over time,but non-significantly.The major significant changes were:reduced plant height;increased harvest index (Fig.2-C and 2-D),and improved resistances to yellow rust and leaf rust.Thus,the yield increase in irrigated winter wheat was associated with reduced plant height and higher partitioning of assimilates into grain.However,no single yield component was responsible for the genetic gain and most likely different varieties had different avenues to productivity enhancement so that in the combined analysis no clear tendency was identified.For instance,the yield structure of the two most recent high-yielding varieties is quite different: variety Ahmetaga has more spikes and grains per spike,but has small kernels;in contrast,Ekiz-2004 had fewer spikes and grains per spike,but larger kernels.

The importance of different yield components for grain productivity can be further clarified by correlation analysis (Table 4).The results show that no single trait demonstrated consistent association with yield across three sites and two years.Under moisture stress the higher yielding varieties in Ankara(2008)had more spikes,fewer grains per spike,and larger grains.The higher yielding varieties in favorable sitesKonya(2009)and Eskişehir(2009)had more grains per spike, and kernel size had no effect on yield.This is evidence that there was variability in the relationship between yield and its components in different environments.High-yielding varieties can be developed,but they may have different combinations of traits leading to their maximum yields.

Table 4–Coefficients of correlation between grain yield and key agronomic traits.

3.3.Rust resistance,grain quality and yield stability

The development of new varieties for irrigated conditions was accompanied by improved rust resistances(Table 5).Field rust severity data were recorded in inoculated nurseries at the Haymana site in Ankara(yellow rust and stem rust)and Adapazari(leaf rust).Of 10 varieties released since the 1990s, nine had high or acceptable levels of stripe rust resistance, including seven categorized with adult plant resistance.Lr34/ Yr18,which confers a durable type of resistance[18],was identified in five varieties out of the 10 varieties.All modern winter wheat varieties released for irrigated conditions are resistant to leaf rust whereas the old variety Yektay-406 is highly susceptible.Stem-rust resistance was variable and two of the modern varieties(Pehlivan and Cetinel-2000)were susceptible.

Grain quality plays an important role in the adoption and continued use of wheat varieties,and motivation provided to farmers to keep by additional payment for higher protein and stronger gluten grain.The benchmark for grain quality is the Russian variety Bezostaya-1,released in Turkey in 1968 and cultivated on up to 1 million ha in the 1990s.Now with the area substantially reduced,it continues as a high quality check for growers and the processing industry.In the process of breeding winter wheat varieties for irrigated conditions the grain quality parameters did not deteriorate,but did not reach the level of Bezostaya-1(Table 3).The best varieties approaching Bezostaya-1 in grain quality were Pehlivan,released in 1998,and the two most recent ones,Ahmetaga and Ekiz-2004.

Stability of grain yield across environments is less important for irrigated wheat compared to rainfed wheat.There is a general notion that modern varieties,while higher yielding and more responsive to inputs,lack the stability of older varieties.Fig.3-A demonstrates that while yield increases the regression coefficient(b)or responsiveness to better conditions increases as well.However,this relationship fits a polynomial function and there are high yielding varieties that are relatively less responsive(Pehlivan and Alpu-2001). On the other hand,the yield ofbetter responding varieties was less stable as seen in Fig.3-B.The higher regression coefficient in the current set of varieties was associated with a higher deviation from the regression line.Bi-plot analysis demonstrated that the recent varieties Eser(12),Ahmetaga(13)and Ekiz-2004(14)are close to the point of the ideal genotype (Fig.4).

4.Discussion

There is one limitation of our study:unequal representation of the breeding periods;there were only four varieties from 1960 to the 1980s and then 10 varieties from 1995 to 2004. Unfortunately,there was a relatively long period in the 1980s and 1990s when very few varieties were released due to administrative policies of the time.However,the current set of irrigated winter wheat varieties represents the major varieties grown on the Central Anatolian Plateau until the early 2010s.The main purposes of this study were to document increase in wheat yields of varieties developed over time and the associated changes in agronomic traits under irrigated conditions to assist in developing a future breeding strategy.The genetic progress was statistically significant(R2=0.657)and genetic improvement was 26.7 kg per year or 0.65%compared to the yield of the earliest variety. Similar genetic gains were reported in other studies[4,7,19]. Genetic gain was generally higher in more favorable locations compared to low-yielding sites.Ortiz-Monasterio et al.[20] reported that as nitrogen inputs increased grain yields (respectively 2867,4608,5299 and 5531 kg ha-1)and annual genetic gains(respectively 32,43,59 and 89 kg per year)increased with 4 nitrogen application levels(0,75,150 and 300 kg ha-1).

Table 5–Rust reactions and resistance gene postulations for the historical set of irrigated winter wheat varieties.

Fig.3–Relationship between:(A)grain yield and regression coefficient(b);(B)regression coefficientand deviation fromregression.

There are two concerns with the genetic gains observed in our study.First,the yields of the most recent varieties seem to plateau.The R2for yield gain analyzed without the two oldest varieties was positive,but marginally non-significant.However,breeding trials conducted with newly released varieties or variety candidates demonstrated that they were higher yielding than varieties Ekiz-2004 and Ahmetaga.Second,the yields of new,more-responsive varieties are less stable and this represents a significant challenge in designing a breeding scheme to combine yield potential and stability.The grain quality of new varieties did not deteriorate over time although most of them were inferior to Bezostaya-1 and this requires attention in future breeding plans.

Fig.4–Results of bi-plot analysis of the historical set of 14 Turkish varieties across 16 environments.The designations of varieties are given in Table 1 and designations of sites are in Table 2.

Correlations between days to heading and grain yield were generally negative and non-significant except for the Konya site with its low yield in 2012(r=0.73**).Some researchers also found negative but non-significant correlations between grain yield and heading date[21].Mohammadi et al.[22] reported a negative,significant correlation between grain yield and heading date under both rainfed and irrigated conditions. Onder[23]reported a negative,significant result under irrigated conditions,and a positive,non-significant result under rainfed conditions.It appears that the relationship between earliness and grain yield depends on both germplasm and environment. In our study under irrigated conditions,this relationship was not important.In several studies on wheat,historical changes in days to heading decreased over the years[4,5,16].However,in our study no change was observed.

Since plant height,biomass,and harvest index are closely related to each other,the general opinion is that as plant height decreases,harvest index increases,provided biomass is stable.We observed a significant reduction in plant height across locations and years.Almost allnew varieties possess the Rht-B1b allele.Harvestindex changed over time from0.28 to 0.36 and there was a significant genetic gain.In the majority of genetic-gain studies,reductions in plant height and increased harvest index over years were reported[4,5,9,20,23].There was no change in biomass over time in our experiment.In some other studies similar results were reported[4,24],but Austin et al.[8]in England and Brancourt-Hulmel et al.[25]in France reported that biomass of new varieties was higher than for old ones.None of the yield components showed significant changes over time in the presentstudy.It appears that different genotypes had different ways of increasing yield so no single yield component made a major contribution.This may be partly attributed to the fact that the varieties used in the study originated from different breeding programs and,hence,have different adaptation mechanisms.

Breeding programs in Turkey have made excellent progress in breeding for stripe rust and leaf rust resistance primarily utilizing adult plan resistance sources.Possibly due to this,there has been no major rust epidemic in Turkey since 2000.The nationalrust pathology research and breeding framework is well integrated,combining pathogen monitoring,field evaluation at hot spot locations,and greenhouse seedling tests to identify the types of resistance and the genes responsible.Resistance to rusts is very important for irrigated conditions and should continue with the same emphasis.

The genetic gains achieved in Turkish irrigated winter wheat varieties can be partly attributed to the utilization ofhigh-yielding spring wheatlines from CIMMYTas parents in the majority of varieties released after 1979.Their utilization also incorporated Rht-B1 gene contributing to height reduction, higher harvest index and grain yield.Most likely they also contributed Lr34/Yr18 and minor genes for rust resistance.On the other hand,the pedigrees of several varieties include Bezostaya-1 or its derivatives as wellas US and Turkish winter wheat varieties.Their contribution reinforced rust resistance as wellas maintaining grain quality.Itappears thatthe diversity of winter wheat parents(Turkey,Eastern Europe and USA)crossed with superior spring wheat germplasm from Mexico subjected to robust selection under local conditions was a key in developing new varieties for irrigated production.

Future challenges include further increases in yield potentialwhile maintaining the grain quality and disease resistance at the backdrop of climate change expressed through higher temperatures and increased frequency of extreme weather events[26].Turkish wheat breeding programs have access to diverse winter wheat germplasm as they host the International Winter Wheat Improvement Program.They are able to utilize the newest superior germplasm from the key breeding programs in Europe and USA.The flow of spring wheat germplasm from CIMMYT-Mexico continues and will be utilized in winter×spring crosses.On the other hand heat during the grain filling and maturity stages becomes an important stress and should be addressed even in the irrigated breeding program.There is a scope for the utilization of new physiological tools already identified in Turkey,like NDVI[27].Field precision phenotyping could be important given the diversity of wheat production environments.Winter wheat breeding cycles remain very slow and it still takes 9-11 years for development and formal submission of new varieties.More efficient utilization of single seed descent or double haploids could accelerate this process and contribute to genetic gains.The recent increased participation of the private sector in seed production and promotion of new varieties will expedite the flow of superior new varieties to the farming community.

Acknowledgments

The International Winter Wheat Improvement Program is supported by CRP WHEAT and Ministry of Food,Agriculture and Livestock of Turkey.Marker analyses for leaf rust and stripe rust resistance genes were provided by Dr.Susanne Dreisigacker,CIMMYT-Mexico.The authors acknowlege the suggestions and editorial work by Dr.Patrick McGuire.

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13 March 2015

in revised form22 July 2015

.

E-mail address:a.morgounov@cgiar.org(A.Morgounov)

Peer review under responsibility of Crop Science Society of China and Institute of Crop Science,CAAS.