Rye (Secale cereale L.)

Rye Breeding
H.H.Geiger and T.Miedaner
Abstract Rye(Secale cereale L.)is mainly a European cereal with about75%of the global production growing in Russia,Belarus,Poland,Germany,and Ukraine.It has the best overwintering ability,and the highest tolerance to drought,salt,or aluminium stress from all small-grain cereals.Harvest is used for bread making, feed,and in growing demands for ethanol and biomethane production as a renew-able energy source.Hybrid rye is competitive to triticale and wheat also on better soils and grown in Germany on about70%of the total rye acreage.Rye developed in the Middle East as a secondary crop,cultivated rye has its greatest diversity in landraces and populations from Central and East Europe.Their utility for breeding has considerably increased by progress in marker-based introgression of donor chromosome segments.Resistance breeding is presently focused on leaf and stem rust(Puccinia recondita,P.graminis f.sp.secalis),ergot(Claviceps purpurea),and Fusarium diseases.Leaf blotch(Rhynchosporium secalis)and soilborne viruses might gain more attention in the future.Main breeding goals are grain yield,straw shortness,lodging resistance,high kernel weight,tolerances to pre-harvest sprouting and abiotic stresses.Population varieties comprise open-pollinated and synthetic varieties.Both are derived from self-incompatible breeding populations which are steadily improved by recurrent half-or full-sib selection.Open pollinated varieties(OPVs)constitute selected fractions of those populations whereas synthetic varieties are composed of specifically selected parents from which they can iden-tically be reconstituted.Most modern population varieties contain germplasm from two or more genetically distant gene pools.Hybrid breeding is based on self-fertile gene pools and cytoplasmic genic male sterility(CMS)is used as hybridizing mechanism.Long-lasting breeding cycles are needed for the development of seed parent lines since testcrossing is only possible after the inbred lines have been converted to CMS analogues by repeated backcrossing.Options to speed up this process are discussed.Development of restorer lines is straightforward once H.H.Geiger(*)
University of Hohenheim,Institute of Plant Breeding,Seed Science,and Population Genetics,
D-70593Stuttgart,Germany,e-mail:geigerhh@uni-hohenheim.de
M.J.Carena(ed.),Cereals,
DOI:10.1007/978-0-387-72297-9,#Springer Science+Business Media,LLC2009157
158H.H.Geiger,T.Miedaner effective restorer genes have been introduced to the respective breeding popula-tions.Recurrent improvement of fertility restoration is most efficiently accom-plished by recombining selected inbred lines after thefirst or second testcrossing mercial hybrid seed production requires well-skilled farmers,careful seed processing,and deliberate logistics since rye produces huge amounts of pollen which may be transported over long distances.Even the slightest genetic contami-nation of the CMS pre-basis and basis seed production may render the respective seed lots worthless for subsequent multiplication.To reduce the cost of thefinal step of seed production,the CMS seed parent and the pollinator parent are grown as a mixture in a95:5ratio.Thus,only about95%of the certified seed consists of true hybrid seed.Whereas the remainder5%are randomly intermated plants of the pollinator.However,the latter generally are poor competitors and therefore do not impair the yielding performance of the‘hybrid’stand.In the last decades,population and hybrid breeding led to substantial progress in grain yield and other traits.
1Introduction
Rye(Secale cereale L.)is a diploid(2n=2x=14)annual,cross-pollinated cereal with an effective gametophytic self-incompatibility system(Lundqvist,1956). Similar to many crops of the Old World,S.cereale evolved in the Fertile Crescent of the Near East.Main regions of diversity are Turkey,Libanon,Syria,Iran,Iraq, and Afghanistan.Rye was,however,never cultivated as a crop there but grew and still grows as a weed within the stands of barley and wheat.Annual rye forms evolved in this agricultural context by natural selection leading to semi-to non-shattering ears,larger kernels,and dormancy(‘primitive rye’).Populations growing at higher altitude show an excellent cold hardiness.Thefirst cultivation of rye took place in the region around the Caspian Sea at about3000–4000BC.Rye came to Eastern Europe by Slavic people.During their migration to the West at about 500BC,they brought the knowledge of rye growing to the Germanic,Celtic,and Finnish peoples.During the whole Middle Ages and modern times till the1960s, rye was the major cereal crop from Germany to Eastern rge breeding progress in the self-pollinated crops,wheat and barley,lead to a decrease of the rye acreage in regions where stress tolerance is less important.On a world-wide basis, rye acreage was nearly halved in the last decade(Table1).Main rye producing countries presently are Russia,Belarus,Poland,Germany,and Ukraine.By far the highest grain yields are obtained in Germany illustrating the high potential of the crop under intensive growing conditions.
Rye is mostly grown as a winter cereal.Spring rye is superior in extremely cold areas or where the snow cover lasts longer pared to other cereals,rye has the best overwintering ability and the highest tolerance to drought, salt,or aluminium stress among all small-grain cereals.Rye excels in considerable growth during late fall and resumes growth very quickly in early spring.Rye is
Rye Breeding159 Table1Main rye growing countries and acreages in1995and2005and average grain yield in
2005(FAO,2006)
Continent/Country Acreage(1,000ha)Yield(t haÀ1)
199520052005 Europe8,6135,620 2.46 Russian Federation3,2501,900 1.91
Poland2,4521,410 2.38
Belarus969580 2.16
Germany861555 5.07
Ukraine552610 1.95
Asia1,126587 1.87
USA374337 1.77
World10,2066,598 2.37
more productive than other cereals on infertile,sandy,or acid soils,as well as on poorly prepared land.Hybrid rye is competitive to triticale and wheat even on better soils due to its higher yield potential.
About50–75%of the harvest is used for bread making.Traditional rye bread is the dark sour bread known in North Germany,Finland,the Baltics,Poland,Belarus, and the Russian Federation.In Sweden,Denmark,and parts of Germany,ryeflour is commonly mixed with25–50%wheatflour for bread making.The remainder rye harvest is used for feeding,the production of alcohol(Schnaps,Vodka),and as a resource for renewable bioenergy(bioethanole,biomethane,and combustion).
2Germplasm and Use of Genetic Resources
Cultivated rye displays a broad range of genetic diversity reflecting the great ecologi-cal differences among the various growing areas.As expected from a cross-pollinated crop,a higher amount of genetic diversity can be found within than among popula-tions(Persson and von Bothmer,2000).A recent marker-based diversity study with landraces and varieties from Nordic countries,Germany,and Poland revealed eight clusters differing in origin(Persson et al.,2006).Large gene bank collections exist in various countries(Table2)comprising East European cultivars,landraces from Europe,Asia,and South America,primitive populations from the Near East,and wild Secale species.In European gene banks,9,901accessions are stored,one-third of which are likely to be duplicated(Podyma,2003).Additionally,236accessions are available from S.silvestre,S.iranicum,and S.montanum.
In practical rye breeding,genetic resources have not been intensively utilized for a number of reasons:(1)exotic germplasm generally lacks adaptation to the targeted growing area,(2)substantial difference in performance between elite and exotic germplasm for polygenic traits,(3)exotic germplasm is lacking inbreeding tolerance,(4)little is known about their genetic distance to established heterotic groups,and(5)genetic phenomena such as pleiotropy,epistasis,and coupling phase linkage between desired and undesired alleles may hinder a direct utilization
(Haussmann et al.,2004).Despite these handicaps,exotic germplasm may contain genomic segments that can improve oligo-and polygenically inherited traits in highly selected breeding populations (de Vicente and Tanksley,1993).
The targeted exploitation of genetic resources is possible by advanced backcross analysis of quantitative trait loci (AB-QTL;Tanksley and Nelson,1996)or via introgression libraries (Eshed et al.,1992).An introgression library consists of a set of lines,each carrying a single marker-defined donor chromosome (DC)segment introgressed from a genetic resource into the background of an elite recipient line (Zamir,2001).Ideally,the introgressed DC segments are evenly distributed over the whole recipient genome and the total genome of the ‘exotic’donor is repre-sented in the set of near-isogenic lines.In rye,two introgression libraries were established with the Iranian primitive rye accession ‘Altevogt 14160’as donor
(Sus
ˇic ´,2005;Falke et al.,2008a)by marker-assisted selection using amplified fragment length polymorphisms (ATLP)and simple sequence repeat markers (Hackauf and Wehling,2002).The libraries comprise 38and 40BC 2S 3lines,respectively,jointly covering approximately 70%of the total donor genome.Most of the introgression lines harbour one to three homozygous DC segments with a mean length of about 12cm.A comprehensive phenotypic evaluation of the libraries revealed considerable genetic variation for quantitatively inherited baking quality traits (Falke et al.,2008)and pollen-fertility restoration (Falke et al.,2009).Thus,these results demonstrate that introgression libraries can serve as a valuable tool for broadening the genetic base of rye breeding as well as for detecting and validating QTL (Zamir,2001).
3Disease Resistance
Important diseases of rye in Central and East Europe are snow mold (Microdochium nivale ),foot rot caused by a complex of Helgardia herpotrichoides ,H.acuformis (syn.Pseudocercosporella herpotrichoides var.herpotrichoides ,var.acuformis ),Table 2Large collections of Secale accessions (Podyma,2003)
Institution Country
No.of accessions N.I.Valivov Institute of Plant Industry
Russia 2,685Botanical Garden of the Polish Academy of Science
Poland 1,630Plant Breeding and Acclimatization Institute,Radzikow
Poland 1,354Leibniz Institute of Plant Genetics and Crop Plant
Research (IPK),Gatersleben
Germany 1,207Research Institute of Crop Production
Czech Rep.659Aegean Agricultural Research Institute
Turkey 512Instituto Nacional de Investigacion y Tecnologia Agraria y
Alimentaria
Spain 428Others Various 1,426
160H.H.Geiger,T.Miedaner
Rye Breeding161 M.nivale,and Fusarium spp.,powdery mildew(Blumeria graminis f.sp.secalis), leaf rust(Puccinia recondita),stem rust(P.graminis f.sp.secalis),leaf blotch (Rhynchosporium secalis and other fungi),ergot(Claviceps purpurea),and Fusari-um head blight(FHB)caused by M.nivale and various Fusarium species.Soilborne cereal mosaic virus(SBCMV),soilborne wheat mosaic virus(SBWMV),and wheat spindle streak mosaic virus(WSSMV),transferred by the soilborne fungus Poly-myxa graminis,cause new diseases in some regions of Germany(Kastirr et al., 2006).For powdery mildew and leaf rust,both qualitative and quantitative resis-tances were reported,whereas quantitative variation was found for foot rot,head blight,and ergot.
In population varieties,the spread of diseases is reduced by collective buffering. Compared with line varieties in self-pollinated crops,rye populations are more likely to harbour resistances accumulated by natural selection(e.g.,Geiger et al., 1988;Mirdita,2006).They can be improved for their disease resistance by recur-rent selection(RS)methods based on half-or full-sib families(HSF or FSF)(cf. Sect.5.1).In hybrid rye,resistance breeding is simplified by the availability of inbred lines for reproducible testing,high genotypic variance between these lines, and the possibility to introgress major genes by backcrossing.
For efficient resistance selection,it is crucial to know the most important population parameters(Table3).Genotypic variance was found to be very large for powdery mildew and leaf-rust resistance caused by both quantitative and qualitative resistances jointly segregating in a population(Wilde et al.,2006).In this case,quantitative resistances can only be detected when the masking effect of the race-specific resistance genes is eliminated by using appropriate pathogen races being virulent to all qualitative resistances.For foot-rot resistance,genotypic variance is significant,but generally low in self-fertile(SF)materials(Miedaner et al.,1995).Selection for lodging resistance does not necessarily lead to a correlated response for foot-rot resistance.
Table3Survey of population parameters determining the gain from selection for resistance to five rye diseases based on experimental results
Parameter Mildew,
Foot rot FHB Ergot
leaf rust
Variance components
Inbred lines per se(L)very large small large moderate LÂenvironment small-moderate moderate large very large GCA++++++++
SCA ns ns(++)ns Heritability high high moderate small-mod Heterosis inconsistent very small moderate mod negative Genetic correlation
Inbreds–hybrids high high ns moderate Trait assessment fast,easy laborous moderate laborous Expected selection gain high mod-small moderate mod-small For details,see text;mod=moderate,ns=non-significant,++=very important,()=not in all years
162H.H.Geiger,T.Miedaner For FHB resistance,genotypic variance between selfed lines is large and thus can easily be exploited.Variation for ergot resistance is available in all materials tested so far including cytoplasmic genic male sterile(CMS)materials and self-incompatible(SI)populations(Mirdita,2006).Environmental effects plays a mod-erate to large role in all pathosystems.Even artificial inoculation with highly aggressive isolates may result in strongly deviating infection levels in different environments and cause significant genotypeÂenvironment interactions.This is especially valid for FHB and ergot resistance.Heritability estimates are generally lower for the latter two resistances compared with resistance to powdery mildew, leaf rust,and foot rot.
General combining ability(GCA)variance is much more important than specific combining ability(SCA)variance in all pathosystems(Table3).The only exception is FHB resistance where significant SCA was found,however,not consistently across years(Miedaner and Geiger,1996).No correlation was found between inbred lines and their hybrids in this pathosystem(Miedaner et al.,2003), in sharp contrast to the other pathosystems.Bothfindings necessitate multi-environmental evaluation of testcross progeny.The use of moderately susceptible testers is crucial to gain a maximum genetic differentiation.Moderate heterosis for resistance was found in FHB resistance.For the foot and leaf diseases,heterosis is practically absent.For ergot resistance,crosses normally display a higher disease severity in terms of weight of sclerotia than their inbred lines(Mirdita,2006). Selection intensity is mainly restricted by the cost of inoculation and trait assess-ment.The wind-borne diseases can be provocated rather easily and scoring at one date on one leaf or even a single whole-plant rating will suffice(Miedaner et al., 2002).The other extremes are foot-rot resistance requiring individual scoring of at least ten stems per plot(Miedaner et al.,1995),and ergot resistance necessitating separation of sclerotia from the grain and determining their weight proportion (Mirdita et al.,2008).
Taking all parameters together,the expected selection gain is highest for mildew and leaf-rust resistance and lowest for foot-rot resistance.For FHB resistance,the necessity to test at the hybrid level substantially reduces the selection gain.These characteristics of the above pathosystems have implications on the method and generation in which selection for disease resistance should be practiced.
In hybrid breeding,mildew and leaf-rust resistance can easily be implemented in the regular line development scheme(cf.Sect.5.2.3)by selecting already in early selfing generations.For all other diseases,specific pre-breeding procedures are required aiming at an increased frequency of resistance alleles in the elite materials. For improving foot-rot and ergot resistance,the introgression of positive alleles from SI elite populations or genetic resources is recommended to increase the genetic variance.Agreement between line and GCA effects allows selection among lines per se,that is,without prior testcrossing.Only for FHB resistance, selection should predominantly be carried out at the non-inbred level.A correlated reduction can then be expected for low deoxynivalenol content.
Since no substantial heterosis for resistance was found in any of the pathosys-tems,selection is necessary in both the seed-and the pollinator-line gene pools.In
Rye Breeding163 the future,experiments designed to estimate population parameters should be combined with QTL analyses.Marker-assisted selection may considerably add to progress in resistance breeding as recently demonstrated for FHB resistance in wheat(Wilde et al.,2007).
4Use and Breeding Goals
Most goals in winter rye breeding are similar to those in other small-grain cereals. Generally,hybrid breeding is moreflexible than population breeding in creating varieties with specific characteristics.
Grain yield is by far the most important trait for rye growers.The average grain yield in Europe presently(2004–2005)varies from1.9t haÀ1in Russia to5.1t haÀ1 in Germany(Table1).Generally,hybrids yield15–20%more than population varieties(cf.Sect.6).
Straw shortness and lodging resistance are important breeding goals.However,since the culm is the major assimilation organ in rye(Nalborczyk et al.,1981),extremely short-strawed rye varieties do not reach high grain yield levels,in particular under severe stress.Therefore,dwarf or semi-dwarf varieties never gained large acreages.
Tolerance to drought and nutrient stress are important components of yield stability because rye is widely grown on poor,sandy pared to wheat, rye has a much higher tolerance to abiotic stresses,such as drought,nitrogen deficiency,and high concentrations of aluminium,zinc,sodium,and acidity.
Baking quality:For milling and baking,mainly a high kernel weight and resistance to pre-harvest sprouting is demanded.Because of its low dormancy, rye kernels may start germinating already before harvest if the weather is warm and moist.This leads to a deterioration of the starch and considerably reduces baking quality.Indirect selection for low a-amylase activity by the falling number method is effective in hybrid materials without negative influence on yield and other agronomic traits(Wehmann et al.,1991).Indeed,some modern German hybrid varieties combine both high yielding performance and high falling number.Another important quality component is a high pentosane content that can indirectly be measured by near-infrared spectroscopy(Rode et al.,2005).
Feeding quality:Rye is increasingly used as an animal feed either on farm or by compound feed producers.The grain is rich in energy and contains more digestible protein and total digestible nutrients than oats or barley and a higher starch content than barley.Rye is not recommended in the diet for weaning pigs,growing chicken, and turkeys and should be restricted to40–50%of the diet for other animals because of its high concentration of pentosanes(Boros,2007).They negatively affect feed intake,feed conversion efficacy,and growth rate in animals.Thus,pentosanes have reverse effects on feeding and baking quality which means that contrasting genetic materials are needed for the two usages.At present,only in Poland,low-pentosane inbred lines are being developed by selecting for low extract viscosity(Madej et al.,1990).
164H.H.Geiger,T.Miedaner Ethanol production:Rye is well suited for ethanol production as a renewable energy source.In the European Union,adding biofuels into gasoline is obligatory. Distiller’s residues are marketed as protein concentrate for pigs,where rye with its favourable protein composition has an advantage over wheat and barley.The grain may not contain mycotoxins or alkaloids caused by Fusarium or ergot infections. Specific breeding goals for high ethanol production are high starch content,high starch yield,and high enzyme activity(Rode et al.,2005).For selecting starch content,the thousand kernel mass can be used as an indirect trait.Protein and pentosan content should be low.
Biomethane production:The use of rye as biomass substrate is rapidly growing in Germany.In humid regions,starting from about800mm of rain,a sequence of forage rye and maize will reach higher biomass yields than maize alone.In spring, rye is the fastest growing winter cereal and excels in a low specific water consump-tion.On the typical dry-warm maize sites,maize alone is safer because soil water may not suffice for growing two crops per year.On dry or cold sites,silage rye may be more economic than maize.Harvest is carried out in the milky ripe stage of grain development when the highest methane yield is obtained.Main breeding goals are high biomass yield and lodging resistance.The methane yield per kilogram dry matter did not differ among rye genotypes.
Forage and pasture:Rye is an excellent forage crop especially when combined with clover and ryegrass.It generally provides more forage than other small grains in late fall and early spring because of its rapid growth and its adaptation to low temperatures.For the same reasons,ryefits well into erosion control programs.For best forage quality,rye should be cut between early heading and the milky ripe stage.Main breeding goals are an early start of growth in spring and high rust resistance.
5Breeding Methods and Techniques
5.1Population Breeding
Population breeding comprises the development of open-pollinated varieties (OPVs)and synthetic varieties(Schnell,1982).In cross-fertilized species like rye,such varieties constitute panmictic populations and can be regrown by the farmer without noteworthy yield reduction.Open-pollinated and synthetic popula-tions differ in their genetic buildup.Whereas the former constitute selected frac-tions of one(or several)breeding population(s),the latter are established by intermating highly selected parental units with subsequent multiplication under open-pollination.The parental units may originate from more than one gene pool.
5.1.1Breeding Open-pollinated Varieties
Over decades,rye breeders used various modifications of a half-sib family (HSF)recurrent selection (RS)scheme for population improvement aiming at OPVs.A typical procedure includes four steps requiring 4years:
1.Selection among equally spaced (e.g.,25Â25cm 2)so-called mother plants mainly for disease resistance,productive tillering,straw stiffness,spike char-acteristics,disease resistance,and general appearance.
2.Progenies of selected mother plants,that is HSFs,are evaluated in unreplicated drilled observations plots at two to three locations.Beside the above traits,lodging resistance,sprouting resistance,and grain quality are important breeding goals at this stage of selection.
3.Multiplication of remnant seed of the best HSFs by open-pollination in plots separated from each other by spatial isolation or by foliar isolation walls or cabins (Fig.1).
4.Multi-environment yield trials of the advanced HSFs,here designated by (HSF)2s,on six-to eight-rowed,5–10m 2plots with one to two replicates per environment.Grain yield,stress tolerance,and lodging resistance are the most important breeding goals at this final selection stage.
To shorten the RS cycle from 4to 2years without renouncing yield trials,the mother plant genotypes can be multiplied by two to three cloning steps before planting.This way,about 20plants per clone can be produced.The clones are transplanted into an isolated field to which the respective breeding population had been drilled some weeks earlier with gaps for the clones such that the latter will completely be surrounded by population plants.This furnishes enough seed of each HSF for unreplicated yield trials on 5m 2plots at three to four locations.A major disadvantage of this otherwise highly effective RS scheme is the great labour demand for cloning,particularly since it has to be accomplished during the most burdening labour peak in autumn between harvest and
planting.
Fig.1Pollination control by foliar walls (left )or cabins (right )
Rye Breeding 165
In the course of time,many breeders changed from HSF to full-sib family (FSF)selection (Fig.2).The latter requires the production of pair crosses under pollina-tion bags in the first year.Because of the self-incompatibility of rye this is possible without emasculation.In the second year,FSFs instead of HSFs are grown in observation plots,and best FSFs are multiplied under pollen isolation in the third year.Finally,in the fourth year,(FSF)2s are evaluated in multi-location yield trials.The expected response to selection is greater for the FS than for the HS scheme because of complete parental control and greater genetic variance between the test units [FSF vs HSF and (FSF)2vs (HSF)2,respectively].However,producing the pair crosses requires a considerably higher experimental input than the corresponding steps in the HS scheme.Furthermore,only a weak selection pressure is possible among the plant pairs in year 1,and more (FSF)2s than (HSF)2s have to be saved after each RS cycle to comply with a minimum effective population size (Walsh,2004).120.000 pairs
2 4.000 FSF 3500 FSF
4500 (FSF)2
New
cycle ~ 20 (FSF)2bulked 20.000
pairs
units
Build up
of OPV Seed multiplication Year Breeding operations Entries
Fig.2Flow diagram and dimensioning example (number of entries)of a full-sib family (FSF )recurrent selection scheme for intrapool population improvement in self-incompatible rye;(FSF)2=progeny of an FSF advanced under open pollination in a pollen isolation device
166
H.H.Geiger,T.Miedaner
As in the HS scheme,cloning the parent plants would allow to half the cycle length of the FS scheme,and the same pros and cons would apply.This high-input short-cycle scheme is well suited as a‘crash’procedure for rapidly increasing the yield level of an otherwise satisfactory breeding population.
Most modern OPVs are built up by merging selected fractions of two or even more genetically distant populations representing a set of heterotic pools.This way, part of the‘panmictic-midparent heterosis’(Lamkey and Edwards,1999)can be used for enhancing the varietal performance.Experimental data(Hepting,1978) indicate that crossing two genetically distant rye populations may increase the yield level of the population cross by10–20%above that of the parent populations. However,at Hardy–Weinberg equilibrium which is rapidly attained during seed multiplication,about half of this increase is lost due to a corresponding drop in heterozygosity.
5.1.2Breeding Synthetic Varieties
The parental components,in short‘parents’,of a synthetic variety can be HS or FS families,clones,inbred lines,or other materials which can be preserved so that the variety can identically be re-composed.However,long-term preservation of rye clones,for example,by in vitro culture,is very difficult and expensive.Clones, therefore,have not gained practical relevance in synthetic breeding so far.Selfing SI genotypes(rather than cloning)is possible if the plants are cultivated at high temperature(30–35 C)shortly before and during anthesis(Wricke,1978).How-ever,only few seeds per spike can be obtained this way and many genotypes don’t respond to the treatment at all.Indeed most synthetics are composed of HS or FS families,and thus OPVs and synthetics basically have the same genetic structure and breadth.
Although SF and SI materials do not differ inflowering characteristics,SF plants display selfing rates of about20–50%under open-pollination(Geiger and Schnell, 1970;Wricke,1979).The resulting inbreeding was shown to drastically lower the performance level of SF synthetics below that of SI synthetics(Singh et al.,1984). Therefore,high-combining SF inbred lines as developed in hybrid breeding are not suited as parents of synthetic varieties.
Selection of parents is mostly based on their intra-pool breeding values as ascertained in RS programs.If parents from two or more heterotic groups are to be combined,it would be desirable to additionally consider their inter-pool breeding values.Production of testcross seed could be accomplished growing the candidates in isolated plots with excessive tester pollen.However,such selection procedures require much higher efforts or take more time to complete a selection cycle than the HS and FS schemes described above.It therefore appears questionable whether inter-pool testing is worthwhile in breeding synthetic rye varieties.Diallel or factorial crosses for estimating SCA effects are not rewarding since SCA variance determines only a negligible part of the genetic differentiation among synthetics.。