Winter Growth Habit Research Articles

Validation of the two-gene epistatic model for vernalization response in a winter × spring barley cross

A two gene epistatic model in which a dominant “winter growth habit” allele at Vrn-H2 encodes a repressor with a corresponding binding site in a recessive vrn-H1 allele explains the vernalization response phenotypes in an array of barley germplasm. In order to validate the model genetically, we developed an F 2 population (and F 2-derived F 3 families) from the cross of Hardy (winter) × Jubilant (spring). Using gene-specific primers, we determined the Vrn-H1 and Vrn-H2 allele architecture of each F 2 plant and we measured the growth habit phenotype of each F 2 plant via phenotyping of its F 3 progeny under controlled environment conditions. We used a set of treatments involving plus/minus vernalization under long photoperiod and vernalization under short photoperiod. Alleles at the two loci showed expected patterns of segregation and independent assortment. Under long day conditions, the two Vrn genes were the primary determinants of heading date, regardless of the vernalization treatment. Under short photoperiod, the effects of these loci were not significant. There was incomplete dominance at Vrn-H1: heterozygotes were significantly later to head than Vrn-H1Vrn-H1 genotypes. Vrn-H2 genotypes were also significantly later to head, even when plants were vernalized. These results validate the two-gene epistatic model for vernalization response under long-day conditions. The results under short photoperiod, and the variance in flowering with vernalization, confirm that while the two Vrn genes are the primary determinants of vernalization response, they are part of a larger interactome that determines the timing of the vegetative to reproductive transition.

Effect of alien 5R(5A) chromosome substitution on ear-emergence time and winter hardiness in wheat-rye substitution lines

Ear emergence time and response to vernalization were investigated in 12 alien substitution lines in which a pair of chromosomes 5A of recipient spring wheat cultivars was replaced by a pair of chromosomes 5R of Siberian spring rye ‘Onokhoiskaya’. The recipients were 12 spring cultivars of common wheat, each carrying different Vrn genes. Spring rye ‘Onokhoiskaya’ had the Sp1 (now called Vrn-R1) gene for spring growth habit located on chromosome 5R, but its expression was weaker. The Vrn-R1 gene had no effect on growth habit, ear emergence time and response to vernalization in wheat-rye substitution lines. Ears emerged significantly later in the 5R(5A) alien substitution lines than in the recipient wheat cultivars with the Vrn-A1/Vrn-B1/vrn-D1 or Vrn-A1/vrn-B1/Vrn-D1 genotypes. No difference in ear emergence time was found between most of the 5R(5A) alien substitution lines and the cultivars carrying the recessive vrn-A1 gene. The presence of the Vrn2a and Vrn2b alleles at the Vrn2 (now called Vrn-B1) locus located on wheat chromosome 5B was confirmed. The replacement of chromosome 5A by chromosome 5R in wheat cultivars ‘Rang’ and ‘Mironovskaya Krupnozernaya’, which carries the single dominant gene Vrn-A1, converted them to winter growth habit. In field studies near Novosibirsk the winter hardiness of 5R(5A) wheat–rye substitution lines of ‘Rang’ and ‘Mironovskaya Krupnozernaya’ was increased by 20–47% and 27–34%, respectively, over the recurrent parents.

Identification of quantitative trait loci and associated candidate genes for low-temperature tolerance in cold-hardy winter wheat

Low-temperature (LT) tolerance is an important economic trait in winter wheat (Triticum aestivum L.) that determines the plants' ability to cope with below freezing temperatures. Essential elements of the LT tolerance mechanism are associated with the winter growth habit controlled by the vernalization loci (Vrn-1) on the group 5 chromosomes. To identify genomic regions, which in addition to vrn-1 determine the level of LT tolerance in hexaploid wheat, two doubled haploid (DH) mapping populations were produced using parents with winter growth habit (vrn-A1, vrn-B1, and vrn-D1) but showing different LT tolerance levels. A total of 107 DH lines were analyzed by genetic mapping to produce a consensus map of 2,873 cM. The LT tolerance levels for the Norstar (LT(50)=-20.7 degrees C) x Winter Manitou (LT(50)=-14.3 degrees C) mapping population ranged from -12.0 to -22.0 degrees C. Single marker analysis and interval mapping of phenotyped lines revealed a major quantitative trait locus (QTL) on chromosome 5A and a weaker QTL on chromosome 1D. The 5A QTL located 46 cM proximal to the vrn-A1 locus explained 40% of the LT tolerance variance. Two C-repeat Binding Factor (CBF) genes expressed during cold acclimation in Norstar were located at the peak of the 5A QTL.

Response of Selected Hard Red Wheat Lines to Imazamox as Affected by Number and Location of Resistance Genes, Parental Background, and Growth Habit

ABSTRACTImidazolinone‐resistant (IR) wheat (Triticum aestivum L.) was released for commercial production in portions of the USA in 2002 and has provided growers with a new technology to selectively control winter annual grass weeds. Imidazolinone herbicides inhibit acetolactate synthase (ALS) in susceptible plants; however, IR wheat has an altered target site which confers resistance to these herbicides. The mutation‐derived resistance trait of most commercially available IR winter wheat cultivars is located on the D‐genome; however, winter and spring wheat cultivars with the resistance trait on the A, B, or D genome or on multiple genomes are currently under development. Four groups of near‐isoline wheat with spring or winter growth habit and resistance genes on the B, D, or both B and D genomes were compared for whole plant and ALS enzyme response to imazamox. Biomass accumulation after treatment was similar among B‐ and D‐ genome resistant winter wheat biotypes and was always higher than B‐ and D‐genome resistant spring wheat biotypes. D‐genome resistant spring wheat was more resistant than B‐genome resistant spring wheat and the two‐gene resistant spring wheat had an additive level of tolerance to imazamox compared with single‐gene resistant spring wheat. Growth habit (spring vs. winter) did not affect in vitro ALS activity among B‐ or among D‐genome resistant cultivars; however, D‐genome resistant cultivars had significantly higher in vitro ALS activity in the presence of imazamox compared with B‐genome resistant cultivars regardless of growth habit. D‐genome resistance appears to provide greater tolerance to imazamox compared with B‐genome resistance; however, multiple‐genome resistance likely will be required to consistently avoid crop injury in spring wheat from labeled U.S. rates. Although ALS extracted from winter wheat and spring wheat responded similarly to imazamox, whole plant responses demonstrates that tolerance is affected by factors other than resistance gene location.

Genotypic Variation of the Ability of Root to Penetrate Hard Soil Layers among Japanese Wheat Cultivars

The hard soil in the field is a major constraint for the cereal production because it mechanically restricts the root expansion and water absorption. The ability of root to penetrate into the hard soil is an important factor affecting yield stability of wheat (Triticum aestivum L.) under hard soil and drought conditions. We investigated the variation in the penetrating ability of roots (PA) among Japanese wheat cultivars and its relationship with other shoot and root characters to acquire basic information to develop the cultivars with a higher PA. The evaluation was conducted by the two experiments using the two groups of cultivars: 1) 43 Hokkaido cultivars in the first experiment, 2) 38 Honsyu, including Shikoku and Kyusyu, cultivars in the second experiment. In each experiment, one seedling of each cultivar was grown in a pot with a disc made of paraffin and Vaseline mixture (PV) as a substitute for the hard soil layer. The number of roots penetrating through the PV disc per plant (NRP), the number of seminal and crown roots reached the PV disc per plant (NRR) and the penetration index (PI = NRP/NRR) of each cultivar were evaluated as the traits related to PA. NRP significantly varied with the cultivar from 4.0 to 29.7 and 3.0 to 22.0 in the first and second experiments, respectively. NRP were significantly correlated with NRR (r=0.644** in the first and r=0.477** in the second experiment) and PI (r=0.863** in the first and r=0.811** in the second experiment), but the relationships between NRR and PI were not significant (r=0.260 in the first and r=0.190 in the second experiment). NRR was significantly correlated with the degree of winter growth habit (requirement of vernalization), root dry weight (DW) above the PV disc, the number of stems and leaf DW in each population. Correlations between PI and other characters were low or not significant. These results indicate that a large genotypic variation exists among Japanese wheat cultivars in NRP, and that PI is a suitable indicator of PA. Cultivars with a high PA detected in this study will be useful genetic resources of wheat to improve the yield stability under drought and hard soil conditions.

Large deletions within the first intron in VRN-1 are associated with spring growth habit in barley and wheat

Mol Gen Genomics (2005) 273: 54–65 DOI 10.1007/s00438-004-1095-4 O R I GI N A L P A P E R Daolin Fu AE Pe´ter Szu } cs AE Liuling Yan Marcelo Helguera AE Jeffrey S. Skinner Jarislav von Zitzewitz AE Patrick M. Hayes Jorge Dubcovsky Large deletions within the first intron in VRN-1 are associated with spring growth habit in barley and wheat Received: 15 September 2004 / Accepted: 22 November 2004 / Published online: 3 February 2005 Springer-Verlag 2005 Abstract The broad adaptability of wheat and barley is in part attributable to their flexible growth habit, in that spring forms have recurrently evolved from the ancestral winter growth habit. In diploid wheat and barley growth habit is determined by allelic variation at the VRN-1 and/or VRN-2 loci, whereas in the polyploid wheat species it is determined primarily by allelic variation at VRN-1. Dominant Vrn-A1 alleles for spring growth habit are frequently associated with mutations in the promoter region in diploid wheat and in the A genome of common wheat. However, several dominant Vrn-A1, Vrn-B1, Vrn-D1 (common wheat) and Vrn-H1 (barley) alleles show no polymorphisms in the promoter region relative to their respective recessive alleles. In this study, we sequenced the complete VRN-1 gene from these accessions and found that all of them have large dele- tions within the first intron, which overlap in a 4-kb region. Furthermore, a 2.8-kb segment within the 4-kb region showed high sequence conservation among the different recessive alleles. PCR markers for these dele- tions showed that similar deletions were present in all the accessions with known Vrn-B1 and Vrn-D1 alleles, and in 51 hexaploid spring wheat accessions previously shown to have no polymorphisms in the VRN-A1 pro- moter region. Twenty-four tetraploid wheat accessions Communicated by W.R. McCombie D. Fu AE L. Yan AE J. Dubcovsky (&) Department of Plant Sciences, University of California, One Shields Av, Davis, CA 95616, USA P. Szu } cs Agricultural Research Institute of the Hungarian Academy of Sciences, 2462 Martonva´sa´r, Hungary M. Helguera EEA INTA Marcos Jua´rez, CC 21, 2580 Marcos Jua´rez, Argentina J. S. Skinner AE J. von Zitzewitz AE P. M. Hayes Department of Crop and Soil Science and Horticulture, Oregon State University, Corvallis, OR 97331, USA had a similar deletion in VRN-A1 intron 1. We hypothesize that the 2.8-kb conserved region includes regulatory elements important for the vernalization requirement. Epistatic interactions between VRN-H2 and the VRN-H1 allele with the intron 1 deletion suggest that the deleted region may include a recognition site for the flowering repression mediated by the product of the VRN-H2 gene of barley. Keywords Wheat AE Barley AE Vernalization AE VRN-1 AE Allelic variation Introduction Many cereal crops, such as wheat, barley and oat, are divided into spring and winter types based on their growth habit. Winter varieties require an extended per- iod of exposure to cold in order to flower, a process known as vernalization. Vernalization is defined as ‘‘the acquisition or acceleration of the ability to flower by a chilling treatment’’ (Chouard 1960). The physiology of vernalization has been studied extensively in cereals, but only a few genes from this molecular pathway are cur- rently known (Yan et al. 2003, 2004b). In wheat and barley, the determination of the ver- nalization requirement involves an epistatic interaction between the genetic loci VRN-1 and VRN-2 (Takahashi and Yasuda 1971; Tranquilli and Dubcovsky 2000). Positional cloning of these two genes from diploid wheat (Triticum monococcum L., 2n=14, genome A m A m ) re- vealed that VRN-1 encodes a MADS-box transcription factor that is orthologous to the Arabidopsis meristem identity gene APETALA1 (Yan et al. 2003), while the VRN-2 gene codes for a zinc finger-CCT domain tran- scription factor with no clear orthologues in Arabidopsis or rice (Yan et al. 2004b). The VRN-1 gene is dominant for the spring growth habit and it is up-regulated by vernalization in winter lines (Danyluk et al. 2003; Tre- vaskis et al. 2003; Yan et al. 2003), whereas the VRN-2

Molecular characterization of the allelic variation at the VRN-H2 vernalization locus in barley

VRN-2 is a dominant repressor of flowering that plays a central role in the vernalization pathway of wheat. This gene is a zinc-finger/CCT domain transcription factor (ZCCT-1) down-regulated by vernalization. In barley, there are three related and linked ZCCT genes designated VRN-H1a, b, and c. A deletion of these three genes was observed in six putative spring induced mutants from winter barley variety ‘Chikurin Ibaraki I’. However, analysis of additional molecular markers demonstrated that these deletions were originated by outcrossing with a spring barley variety carrying the natural ZCCT deletion. Hybridization of Southern blots from 84 barley varieties with a wheat ZCCT1 probe showed three or more fragments in 23 winter varieties but none in 60 out of the 61 vrn-H2 spring varieties. The vrn-H2-spring barley variety ‘Fan’ showed only the ZCCT-Hb gene, suggesting that this gene is not sufficient to determine winter growth habit in barley. We also show in this study, that the effect of VRN-H2 on flowering time completely disappears in the presence of the dominant Vrn-H1 allele in a Morex × Hordeum spontaneum segregating population. A different result was described before for the epistatic interactions between the orthologous genes in diploid wheat. We discuss the possible causes of these differences.

Large deletions within the first intron in VRN-1 are associated with spring growth habit in barley and wheat

The broad adaptability of wheat and barley is in part attributable to their flexible growth habit, in that spring forms have recurrently evolved from the ancestral winter growth habit. In diploid wheat and barley growth habit is determined by allelic variation at the VRN-1 and/or VRN-2 loci, whereas in the polyploid wheat species it is determined primarily by allelic variation at VRN-1. Dominant Vrn-A1 alleles for spring growth habit are frequently associated with mutations in the promoter region in diploid wheat and in the A genome of common wheat. However, several dominant Vrn-A1, Vrn-B1, Vrn-D1 (common wheat) and Vrn-H1 (barley) alleles show no polymorphisms in the promoter region relative to their respective recessive alleles. In this study, we sequenced the complete VRN-1 gene from these accessions and found that all of them have large deletions within the first intron, which overlap in a 4-kb region. Furthermore, a 2.8-kb segment within the 4-kb region showed high sequence conservation among the different recessive alleles. PCR markers for these deletions showed that similar deletions were present in all the accessions with known Vrn-B1 and Vrn-D1 alleles, and in 51 hexaploid spring wheat accessions previously shown to have no polymorphisms in the VRN-A1 promoter region. Twenty-four tetraploid wheat accessions had a similar deletion in VRN-A1 intron 1. We hypothesize that the 2.8-kb conserved region includes regulatory elements important for the vernalization requirement. Epistatic interactions between VRN-H2 and the VRN-H1 allele with the intron 1 deletion suggest that the deleted region may include a recognition site for the flowering repression mediated by the product of the VRN-H2 gene of barley.

Genetic Variation in Component Traits of Heading Date in Hordeum vulgare subsp. spontaneum Accessions Characterized in Controlled Environments

Ancestral germplasm may be a useful source of genetic variation for crop improvement. Genetic variation in developmental traits that contribute to heading date may be useful in developing varieties that are uniquely tailored to specific stress environments. Hordeum vulgare subsp. spontaneum (K. Koch) A. & Gr. is the ancestor of cultivated barley and useful developmental trait alleles may have been lost in the domestication process. Accordingly, we surveyed a sample of 16 subsp. spontaneum accessions for vernalization requirement, photoperiod sensitivity, photoperiod response, and relative earliness. We compared the subsp. spontaneum accessions to four H. vulgare L. subsp. vulgare accessions representing spring, facultative, and winter growth habit. Thirteen subsp. spontaneum accessions originating from the Fertile Crescent and the one subsp. spontaneum accession from the Caucasus region required vernalization; they were responsive to long photoperiods and most were very early. Two subsp. spontaneum accessions from the Himalayan region had no vernalization requirement but were extremely sensitive to short photoperiods. We used a clustering procedure to define two groups of subsp. spontaneum accessions, a group of subsp. spontaneum that included the two subsp. vulgare accessions of spring and facultative growth habit, and a fourth group comprised of the two subsp. vulgare winter habit cultivars. These data indicate that subsp. spontaneum may be a source of novel alleles for growth habit.

RFLPs in Cultivated Barley and Their Application in the Evaluation of Malting Quality Cultivars

Molecular markers provide powerful tools for characterizing plant genetic resources for crop improvement purposes. A set of 182 barley cultivars representing six different countries were surveyed for restriction fragment length polymorphisms (RFLPs) using 45 clones distributed over all seven barley chromosomes. Polymorphism was detected with every clone, by the use of at least one restriction enzyme per clone (referred to as a locus), and up to 12 alleles were detected per RFLP locus. RFLP patterns were compared among different barley groups formed by subdividing the samples on the basis of country of origin, spring or winter growth habit, and two- or six-rowed spikes. The results indicated that genetic differentiation among different geographical groups was more profound than between spring and winter types, followed by differences between two- and six-rowed barley. Application of the RFLP information to the evaluation of genetic variation in barley cultivars from the United Kingdom indicated a significantly reduced level of molecular polymorphism among malting barley, especially among spring malting lines. It was suggested that the incorporation of exotic germplasm may be desirable in malting barley breeding programs in order to reduce the vulnerability of the crop.

Genetics of Growth Habit (Spring vs. Winter) in Tetraploid Wheats: Production and Analysis of Near-Isogenic Lines

Variability in tetraploid wheat species for growth habit (spring vs. winter) was studied in the field and, as a result, winter growth habit samples were identified. Backcrossing on the background of Tririmn tlicoccum cv. Black Winter Emmer developed the near-isogenic lines BSlE and BS2E carrying the dominant genes Vrn1 and VvnZ, respectively. The donors of the dominant genes Vrnl and VrnZ were Pugsley's common wheat near-isogenic lines Triple Dirk D and Triple Dirk B, respectively. The results demonstrated that T. clicoccum near-isogenic lines with the dominant Vm genes do not mature significantly later than the near-isogenic lines of common wheat. Wheat as a major food crop will reindin a plant of undiminishing perennial research interest. The genetics of common wheat, Triticum aestivum L. has been studied more than in the other wheat species. More recently, the genetics of these species has stirred interest with reference to genetic erosion of common wheat, especially the genetic control of resistance to pathogens or insects, and adaptation to environments. Growth habit (spring vs. winter) is very important for the adaptation of wheat cultivars to diverse climates. The winter habit of wheat is characterised by delayed ear-emergence in the absence of cold treatment (vernalization). This mechanism prevents the onset of floral development during winter. Spring wheat has a little or no vernalization response. The spring growth habit is dominant to winter growth habit. It has been previously shown that the Vrn genes controlling growth habit in wheat act not only when the plants developmental program switches to spring or winter growth habit, but also when the developmental phases are enfolding, i.e., control of the duration of the life cycle from shooting to ear emergence and, as a consequence, affect earliness and yield (For references, see reviews FLOOD

The wheat VRN2 gene is a flowering repressor down-regulated by vernalization.

Plants with a winter growth habit flower earlier when exposed for several weeks to cold temperatures, a process called vernalization. We report here the positional cloning of the wheat vernalization gene VRN2, a dominant repressor of flowering that is down-regulated by vernalization. Loss of function of VRN2, whether by natural mutations or deletions, resulted in spring lines, which do not require vernalization to flower. Reduction of the RNA level of VRN2 by RNA interference accelerated the flowering time of transgenic winter-wheat plants by more than a month.

Growth and yield responses of spring and winter triticale cultivated under Mediterranean conditions

Eight hexaploid triticale genotypes, five of spring and three of winter growth habit were used to study biomass production, contribution of the pre-anthesis assimilates to the grain yield, and their relationship to grain yield. Genetic effects for biomass production were found at anthesis but not at maturity. Growth-habit explained most of the detected differences for biomass production: winter triticale had around 15% higher dry matter than spring triticale at anthesis. However, the higher accumulated thermal time from sowing to anthesis could explain the observed differences, since the correlation coefficient between both variables was 0.78 ( P<0.001, n=24). Dry matter translocation (DMT) was 30% higher for winter than for spring triticales, representing a contribution to the grain yield of 60.9% for winter genotypes and 42.0% for spring ones. However, grains were 26.8% heavier in spring than in winter triticales, and, finally, spring triticales yielded around 21% more than winter types. For spring genotypes, crop dry weight at anthesis was positively related to yield, whereas for winter triticales the relationship for these two variables was negative. Highest values of triticale grain yield were reached when time from sowing to anthesis was comprised, approximately, between 1350 and 1420 growing degree-days (GDD), decreasing before and after this interval. Thus, time to anthesis for spring triticales were included into the optimum interval, which permitted to reach higher grain yield. We could conclude that spring triticales are much more adapted than winter triticales for grain production under Mediterranean conditions.

Patterns of grain filling of spring and winter hexaploid triticales

Eight hexaploid triticale genotypes, five of spring and three of winter growth habit were used to study the genetic variability of grain filling characteristics and their relationship with grain yield. Four trials were carried out under rainfed and irrigated conditions in Northeast Spain. Grain dry weight data was fitted to a logistic curve. Genetic variability existed for the length of the period from sowing to anthesis, maximum grain filling rate and maximum grain weight. Most of this variation was associated to the growth-habit of the genotypes. Winter triticales required 11% more thermal-time from sowing to anthesis, and had a maximum grain weight, which was 25% lower than that of spring genotypes. The maximum grain filling rate was 40% higher in spring than in winter triticales. Grain filling duration was mainly controlled by environmental conditions, and was not correlated with grain yield. A negative phenotypic correlation was detected between grain filling duration and maximum grain filling rate ( r p=−0.41, P<0.05), and a positive correlation between maximum grain weight and maximum grain filling rate ( r p=0.77, P<0.001). Spring genotypes yielded around 21% more than winter types, probably because they escaped from terminal water stress. Grain yield was strongly correlated phenotypically and genetically to the maximum grain weight ( r p=0.87, r g=0.92, P<0.001) and maximum grain filling rate ( r p=0.78, P<0.001; r g=0.79, P<0.05). Short duration from sowing to anthesis, high grain filling rate and high maximum grain weight seem to be major traits to optimise triticale grain yield under Mediterranean conditions.

Epistatic interaction between vernalization genes Vrn-Am1 and Vrn-Am2 in diploid wheat.

Genes Vrn-A(m)1 and Vrn-A(m)2 control the vernalization requirement in diploid wheat (Triticum monococcum). The epistatic interaction between these two genes on flowering date was studied here using a factorial analysis of variance. One hundred and two F2 plants were classified according to their genotypes for molecular markers tightly linked to Vrn-A(m)1 and Vrn-A(m)2. Mean comparisons showed that the VrnA(m)2 allele for winter growth habit was dominant to the vrn-A(m)2 allele for spring growth habit and that the Vrn-A(m)1 allele for spring growth habit was dominant to the vrn-A(m)1 allele for winter growth habit. A significant interaction was found between these two genes, suggesting that they work in the same developmental pathway. Plants homozygous for the recessive vrn-A(m)2 allele for spring growth habit flowered earlier than plants from the Vrn-A(m)2 class independently of the alleles present at Vrn-A(m)1. However, differences in heading date between plants with the Vrn-A(m)1 allele and those with the vrn-A(m)1 allele were significant only when the dominant Vrn-A(m)2 allele was present. A genetic model for the action of these two vernalization genes is proposed in which the role of Vrn-A(m)1 is to counteract the Vrn-A(m)2-mediated delay of flowering.

Geographical Distribution of a Chromosome 7C and 17 Intergenomic Translocation in Cultivated Oat

Previous cytogenetic and molecular genetic investigations have shown variation for the presence of intergenomic translocation segments on chromosomes 7C and 17 of common cultivated oat (Avena sativa L., 2n = 6x = 42) and red oat (A. byzantina K. Koch, 2n = 6x = 42). The objective of this work was to determine the geographic distribution of these translocation segments in 197 landraces and cultivars using C‐banding. Genotypes were selected primarily on the basis of diversity of geographic origins, particularly within the Mediterranean‐Near Eastern center. Eighty‐nine percent of traditional A. byzantina‐type accessions, mostly from the lowland Mediterranean basin and Indian subcontinent, were of the nontranslocation type. Ninety‐seven percent of traditional A. sativa and hulless (A. sativa subsp. nuda) genotypes possessed the 7C‐17 translocation (Δ7C‐17) segments. Presence or absence of the Δ7C‐17 was more loosely associated with spring vs. winter growth habit, but still highly significant. The results support the hypothesis that common cultivated oat and red oat are distinct races of the hexaploid biological species and were domesticated independently of one another.

Leaf Rust Resistance of Spring, Facultative, and Winter Wheat Cultivars from China.

Leaf rust, caused by Puccinia triticina, is an important disease of wheat (Triticum aestivum) in China. Sixty-one spring and 102 facultative or winter growth habit wheat cultivars from China and a set of testers, carrying named Lr genes, were evaluated for resistance at the seedling growth stage with an array of Mexican Puccinia triticina races. Variation in seedling infection types of the cultivars was compared with that of the testers, and genes conferring low infection types were postulated. In total, nine named genes, Lr1 (in 13 cultivars), Lr3 (12), Lr3bg (2), Lr10 (1), Lr13 (4), Lr14a (1), Lr16 (49), Lr23 (9), and Lr26 (81), were identified. Thirty-one cultivars displayed intermediate reactions to one or more races that could not be attributed to any named gene. Twenty-eight spring cultivars were also evaluated at two field sites in Mexico using two common races. About half of them displayed good to moderate adult resistance that may be partly due to the presence of slow rusting gene Lr34 in at least seven cultivars. Diversity in adult plant responses of these wheats indicated the presence of additional slow rusting genes. Presence of 1B.1R translocation in 12 wheat cultivars, supposedly derived from intergeneric crosses involving T. durum, Haynaldia villosa, and Avena fatua, indicated that their pedigrees were incorrect.

Effect of the Vrn1‐Fr1 Interval on Cold Hardiness Levels in Near‐Isogenic Wheat Lines

We investigated the feasibility of cold hardiness manipulation in wheat, Triticum aestivum L., with the Vrn1-Fr1 interval on chromosome 5AL. The interval contains a gene(s) that has influenced vernalization requirements and cold hardiness levels. We conducted LT 50 tests (lethal temperature of 50% of plants) on wheat NILs (near-isogenic lines) that differed for alleles at the Vrn1-Fr1 interval, to determine the effects of the interval on cold hardiness levels between hardy and nonhardy wheat. The NILs were derived from five backcrosses between a spring wheat recurrent parent, 'Marfed', and two winter wheat donor parents, 'Suweon 185' and 'Chugoku 81', hardy and nonhardy, respectively. The developed populations were Suweon 185/6*Marfed and Chugoku 81/6*Marfed spring and winter NILs. Results showed that the winter NILs could tolerate a 4.3 °C colder LT 50 score than the spring NILs, and that the Suweon 185/6*Marfed winter NILs could tolerate a 0.5 °C colder LT 50 than Chugoku 81/ 6*Marfed winter NILs. Results indicate that the Vrn1-Fr1 interval explained between 71 and 91% of the variation for LT 50 scores between these genotypes. The NILs were analyzed with the probe Xwg644 to confirm linkage with the Vrn1-Fr1 interval and to determine its utility as a marker for vernalization requirement and cold hardiness. EcoRI-digested DNA of the winter and spring NIL wheat, probed with Xwg644, showed that a 9.7-kb band co-segregated with the winter growth habit. Results indicate that differences in cold hardiness levels between winter wheat cultivars may be explained by this interval and that the interval may be manipulated through plant breeding to improve the cold hardiness of cultivars.

Characterization and Analysis of North American Triticale Genetic Resources

A collection of more than 3000 accessions of triticale (× Triticosecale Wittmack), called the North American Triticale Genetic Resources Collection (NATGRC), was assembled from 10 active and inactive breeding programs in the USA, Canada, and Mexico for the purposes of conservation, characterization, evaluation, and documentation. Since triticale has no wild ancestors and hybrid parentage is often unknown, preservation of unique gene combinations is essential for continued utilization. The origin groups that comprised the whole collection were evaluated in field plots for 2 yr at Davis, CA. Accessions were predominantly secondary hexaploid triticales having spring growth habit. The collection was classified for spike type and 38% had spikes typical of complete (Beagle type) and 30% were substituted (Armadillo type) triticale. The Shannon‐Weaver diversity index (H′), computed for seven qualitative traits, was 1.275 for the whole colleclion. The most diverse group was from Manitoba (1.404) and the least diverse groups were from Oregon (0.822) and CIMMYT (0.867). Overtrait mean coefficients of variation for eight quantitative traits gave similar diversity ratings as H′ for each of the origin groups (r = 0.74*), suggesting that simply scored traits may be useful for assessing overall diversity in large genetic resource collections. Principal components (PC) analysis of quantitative traits showed differentiation, but considerable commonality, among the Canada, Mexico, and USA groups. The CA‐Davis group included hybrid derivatives from CA‐Jenkins × CIMMYT groups that clustered intermediate to those groups, suggesting a genetic basis for the phenotypic clustering. The PC analysis showed that the Beagle and Armadillo types differed in several quantitative traits, showing that this classification is a useful descriptor for hexaploid triticale. The NATGRC is conserved at USDA, Aberdeen, ID, and CIMMYT, Mexico. Researchers are urged to use and contribute to this collection. The formation of a European‐based collection emphasizing winter growth habit is recommended.

Photoperiodic response and its relation to earliness in wheat

The photoperiodic response of 15 spring and winter varieties was observed. Vernalised plants were grown under long-day (light period longer than 14-hours) and under short-day conditions (light period 10-hours). The earliness under long-day condition and the photoperiodic responses were significantly different amongst the tested varieties. The earliness under long-day conditions depended on photoperiodic response. The winter-spring vernalisation requirement influenced earliness but did not influence photoperiodic response. Varieties with spring growth habits that had the same or similar photoperiodic response to varieties with winter growth habit were earlier in heading. The tested varieties that came from lower geographical latitudes were usually earlier and less photoperiod sensitive than the varieties from higher geographical latitudes.