Hybrid chlorosis in wheat × rye crosses

Fourteen accessions of rye when crossed to Triticum aestivum cv. C 306 (Ne1ne2ch1Ch2) yielded chlorotic F1 hybrids and six accessions involved in hybrid combination with the same tester produced normal F1 hybrid plants. Two rye accessions, namely, EC 179188 and EC 143825 when crossed to the wheat lines HD 2329 (ne1Ne2ch1Ch2) and NI 5439 (ne1ne2ch1Ch2) also produced chlorosis. The hybrids between T. macha and two rye accessions produced normal plants. Variable degrees of chlorosis were observed among different wheat × rye F1 hybrids. It is suggested that the rye accessions producing chlorosis in combination with wheat cvs. C 306, HD 2329 and NI 5439 (all Ch2-carriers) carry one of the complementary genes for chlorosis. Gene symbol Chr1 is proposed for the chlorosis gene of rye.     

Chromosome locations of genes controlling ‘purple leaf base’ in rye and wheat

Summary Purple leaf base is expressed only if there is anthocyanin pigmentation in coleoptiles either in rye or in rye-wheat-additions. Genes controlling purple leaf base were found to be located on chromosomes 5R (An5), 4B (Ra2) and 6B (Ra3) using the trisomic set of rye cv. Esto and autoplasmic rye-wheat-additions, respectively.     

Embryo lethality in wheat × rye hybrids—mode of inheritance and the identification of a complementary gene in wheat

Crosses between hexaploid wheat and rye can only succeed when pre- and post-zygotic barriers have been overcome. A rye gene determining embryo lethality (Eml-R1), which is involved in post-zygotic isolation, has been mapped to chromosome 6R. In the present paper the mode of inheritance of Eml-R1 was studied by employing a wheat/rye chromosome 6R addition line. We show that Eml-R1 exists in at least two alternative forms, with the mutant allele Eml-R1b being dominant with respect to wild-type Eml-R1a. Furthermore, we have exploited nulli-tetrasomic lines of wheat to detect a complementary wheat gene present on chromosome 6A. This gene has been designated Eml-A1.     

A wheat–Thinopyrum ponticum–rye trigeneric germplasm line with resistance to powdery mildew and stripe rust

An individual plant, line 0-123-1-1 with the chromosome number 2n?=?42 was obtained in the BC₃F₄ progeny of a cross between a wheat 1BL.1RS translocation line 48112 and wheat?CThinopyrum ponticum partial amphiploid BE-1. Molecular markers specific for 1RS, Glu-B3, and the T. ponticum genome specific marker SCAR₉₈₂ revealed that the line was trigeneric having alien chromatin from both T. ponticum and rye. Resistance tests with mixed races of Blumeria graminis f. sp. tritici and an individual race of Puccinia striiformis at the seedling and adult stages revealed that 0-123-1-1 was immune to powdery mildew and stripe rust for the whole growth period. High levels of disease resistance and good and stably agronomic traits make the 0-123-1-1 line a good germplasm for breeding in wheat.     

Inheritance of late maturity α-amylase in wheat

Summary Two wheat cultivars that consistently show high levels of grain -amylase at harvest ripeness, in the absence of preharvest sprouting, were crossed with a control, low -amylase cultivar, and F₁, F₂ and BC₁ populations were developed. Grain of these populations was analysed for -amylase activity at harvest ripeness. Distribution and segregation patterns were consistent with control at a single locus with high -amylase the recessive allele. This mode of inheritance would make it extremely difficult to differentiate homozygous low -amylase lines from heterozygotes (low -amylase phenotype but carriers of high -amylase) and has important implications for wheat breeders. High -amylase, termed late maturity -amylase, was not linked with the awned inhibitor gene, B2, located on the long arm of chromsome 6B.     

Development and characteristics of ω-gliadin-free wheat genotypes

Omega gliadin proteins are one of the most allergenic components of wheat gluten. Proteins of the ω-5 subgroup are recognized as main allergens causing wheat dependent exercise induced anaphylaxis—the most dangerous, life-threatening IgE mediated food allergy. A set of wheat genotypes lacking all ω-gliadins has been developed by cumulating inactive gene variants in three gliadin coding loci (Gli A1, Gli B1 and Gli D1), using traditional plant breeding methods. Endosperm proteins of ω-gliadin-free genotypes were compared to a control genotype containing all ω-gliadins by A-PAGE, SDS-PAGE and RP-HPLC. A considerable decrease (about 30 %) of gliadin immunoreactivity as a consequence of ω-gliadin elimination was demonstrated by ELISA, using sera of ten patients allergic to gluten. Preliminary evaluation of the technological properties of the ω-gliadin-free genotype by the SDS sedimentation test suggests that elimination of all ω-gliadins may also significantly improve wheat bread making quality.     

The nuclear–cytoplasmic interaction controls carotenoid content in wheat

In greenhouse studies of three alloplasmic wheat series, plant height, flowering date and yield per plant were least affected when the native cytoplasm was replaced by donor cytoplasm of the Triticum–Aegilops complex than when replaced by Hordeum chilense cytoplasm. On the other hand, significant differences for seed lutein content were found between euplasmic controls and their respective alloplasmic lines in all the alloplasmic lines studied, underscoring the important role of the cytoplasm to determine the seed carotenoid content. Both T. aestivum subesp. macha and Ae. squarrosa cytoplasms increased the lutein content. They may be the most useful sources of cytoplasmic variability for broadening the genetic diversity of wheat for seed carotenoid content since both cytoplasm types do not produce any detrimental effect on agronomic traits, as previously reported by other researchers. These findings demonstrate the role of the nuclear × cytoplasm interaction in the accumulation of carotenoids in wheat.     

Golden calves or white elephants? Biotechnologies for wheat improvement

The 1990s have seen an acceleration in the development of new biotechnologies which can increase the efficiency of wheat breeding by providing new and novel sources of variation, speeding up the breeding cycle, and increasing the efficiency of selection. This paper reviews the most significant technologies and their probable impact on wheat breeding into the next millennium. Amongst techniques developed from the application of tissue culture methods, doubled haploid systems are at last making a contribution through the development of the maize pollination system. By the introduction of various improvements, this is now efficient enough to produce material from a range of adapted genotypes in large numbers, and varieties are entering national list trials from this system. Developments in tissue culture have also led to the realistic possibility of genetically engineering wheat, based on biolistic methods of gene delivery into immature embryos. Some problems relating to gene stability and expression remain to be resolved, but targets, particularly with respect to disease and pest resistance and end-use quality, are now being actively pursued. The development of the genetic wheat map using molecular marker systems has revolutionalised the power of genetical analysis in wheat, enabling agronomic trait loci, whether major genes or QTL, to be identified, located and 'tagged'. Additionally, strategies for the molecular cloning of loci are being developed, particularly by exploiting a comparative mapping approach which combines the genetical information from all cereals in a common framework. This will lead to tools for modifying crop phenotype in a directed fashion to produce improved and novel phenotypes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Selecting winter/facultative wheat genotypes from spring × spring crosses

F₂ populations derived from a half diallel cross between 11 spring bread wheat cultivars were classified according to segregation for heading date in a spring environment. Seventeen populations segregated very late plants, presumably of winter type, resulting from the presence of different Vrn genes in the parents. The objective of the study was to evaluate the performance of these spring x spring crosses grown in a winter wheat environment. F₂ plants were selected from six populations and were simultaneously exposed for several generations to the winter wheat environment (Toluca, Mexico, winter) and spring wheat environment (Ciudad Obregon, Mexico, winter; Toluca, spring). Visual selection was conducted on F₃-F₅ populations for agronomic type relevant to the environment under which the segregating generations were grown. The lines grown in the spring environment performed very well and a number of them were promoted to advanced generation testing. The same lines grown in the winter environment suffered from frost and were almost entirely discarded, proving that spring × spring crosses have limited value for germplasm improvement targeted for conditions similar to the Toluca highland winter environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Has yield stability changed with genetic improvement of wheat yield?

The effect of plant breeding on yield and their physiological determinants has been widely studied in wheat. However, it is poorly understood how, and to what extent, yield stability has been modified. To attempt a direct analysis of changes in absolute and relative yield stability, data of yield of cultivars released in different eras in different environments were obtained from records from our lab and from the literature. Depending on the availability of data, effects of plant breeding on yield stability of cultivars released in Argentina, Australia, Italy and the United Kingdom were evaluated using a quantitative approach. In this paper it was assumed that the slope of yield vs. environmental index estimates the instability of the cultivars. In addition, a more qualitative approach for Mexico, and the former USSR complemented this analysis. There was a clear decrease in yield stability assessed in absolute terms as a consequence of wheat breeding. In Argentina, Australia, Italy and the UK this decrease was related to the magnitude of yield increases. However, the decrease in yield stability in Argentina and Australia was less than for Italy and the UK, particularly so during the last 30 years. Modern cultivars released in Argentina and Australia showed a trend to maintain yield stability as a percentage of their yield similar to that of their predecessors, while the two European countries analysed tended to a slight decrease in yield stability even in relative terms. The complementary, less quantitative evaluation of Mexico and the former USSR appeared to confirm the quantitative trends described for the other countries, i.e. a general decrease in yield stability (assessed in absolute terms) with genetic gains in yield potential. This revised version was published online in July 2006 with corrections to the Cover Date.     

Breeding for Fusarium head blight resistance in wheat—Progress and challenges

Fusarium head blight is among the most extensively studied fungal diseases of wheat and other small grain cereals due to its impact on yield and quality, but particularly due to its potential to produce mycotoxins, which are harmful to humans and animals. Since our last comprehensive review on QTL mapping and marker-assisted selection for FHB resistance in wheat in 2009, numerous studies have been conducted to identify, validate or fine-map resistance QTL. The main aim of this review is to update and summarize findings on FHB resistance breeding of wheat published during the last decade. Furthermore, we compiled a user-friendly table listing FHB resistance QTL data providing a valuable resource for further FHB resistance research. The role of morphological and phenological traits on FHB resistance and possible consequences for resistance breeding are discussed. This review concentrates current knowledge on breeding for FHB resistance and suggests strategies to enhance resistance by deploying molecular breeding methods, including marker-assisted and genomic selection.     

Chloroplast degeneration as a consequence of “hybrid necrosis” in wheat

The results of a cytological study of hybrid necrosis in wheat are presented. Two types of necrosizing of the leaves have been found viz. necrosis via dull green discoloration, and necrosis via a yellow intermediate colour. In the first case the conglomeration of the cell contents starts when the size of the chloroplasts is only little reduced. In the second case the chloroplasts become very small before forming small lumps or bunches. It is suggested that the conglomeration of the cell contents is more disastrous for the plant than the decrease in size of the chloroplasts. The problem of the genetical and physiological causes of hybrid necrosis is discussed.     

Expression of late maturity α-amylase in wheat containing gibberellic acid insensitivity genes

Summary Two wheat cultivars, Spica and Lerma 52, which consistently produce high levels of -amylase during the later stages of grain development (late maturity -amylase), were crossed with a set of four near-isogenic lines carrying the tall (rht) allele or one of the dwarfing genes Rht1, Rht2 or Rht3 (GA-insensitive alleles). The F₁ and F₂ populations were developed and analysed for grain -amylase and plant height. The Rht3 gene exhibited the strongest influence on plant height and strongly inhibited new -amylase synthesis during the later part of grain ripening. By comparison, Rht1 and Rht2 had a less pronounced effect but still significantly reduced the expression of late maturity -amylase. These observations suggest that gibberellic acid is involved either directly or indirectly in this phenomenon. The implications of the effect of dwarfing genes on expression of late maturity -amylase are discussed in relation to cultivar improvement and to the identification and control of high -amylase germplasm.     

Genetics of stem rust resistance in the durum wheat accession ‘Reichenbachii’

Summary Inheritance of seedling reactions to cultures of races TLM and MBCT of Puccinia graminis f.sp. tritici was studied in crosses of the resistant durum Reichenbachii with susceptible Marruecos 9623 and DZ04-118. The Chi-square test for goodness of fit was used to analyze segregating populations. Two independent recessive genes appeared to control resistance of Reichenbachii to both TLM and MBCT. Depending upon the cross, the two genes interacted cumulatively to condition immunity or higher levels of resistance than either parent conditioned singly. There was no evidence of maternal influence on the inheritance of resistance. Resistance genes in Reichenbachii were recessive; therefore, breeders should consider the use of relatively large F₂ populations to effectively transfer these genes to cultivars with good agronomic characteristics.     

Monosomic analysis of fertility restoration in common wheat ‘Prof. Marchal’

Summary In common wheat (Triticum aestivum L.) a monosomic set of Chinese Spring and male-sterile Janus (with cytoplasm of T. timopheevi Zhuk.) were used to determine the chromosomal location of Rf-genes in Professeur Marchal. As revealed by test cross data, a major gene cofeerring fertility restoration was present in Prof. Marchal on chromosome 1B. A significant deviation towards sterility was observed in some fest cross progenies. Chromosome 1B of Chinese Spring appeared to carry a dominant restoring gene, which caused partial restoration of fertility.     

Genetic control of a response to the segregation distortion allele,Sd-1d,in the common wheat line ‘Indis’

Summary A translocated chromosome segment, derived from Thinopyrum distichum, carries the leaf rust resistance allele Lr19d and a segregation distorter allele, Sd-1d. In translocation heterozygotes, male and female gametophytes lacking the translocation are aborted, the severity of the effect depending on the genotype of the hybrid. The selective abortion of the gametophytes with a normal chromosome 7D appears to be based on the absence of the translocated chromosome rather than the presence of the normal chromosome. The magnitude of the gametocidal response, elicited by Sd-1d, is under multigenic control. A number of chromosomes, the individual effects of which are generally small, may act to suppress or promote the response. Chromosome arms 2AL, 2BL, 5BL and 5DL of Chinese Spring were found to reduce sensitivity to the presence of the gametocidal chromosome. Chromosome 3B of Inia 66-1 also reduce the gametocidal response while chromosome arm 6DS of Chinese Spring may promote the effect     

Selection of U and M genome-specific wheat SSR markers using wheat–<Emphasis Type="Italic">Aegilops biuncialis</Emphasis> and wheat–<Emphasis Type="Italic">Ae. geniculata</Emphasis> addition lines

We selected wheat SSR markers specific to the U and M genomes of Aegilops species. A total of 108 wheat SSR markers were successfully tested on Ae. biuncialis (2n = 4x = 28, U^bU^bM^bM^b), on five wheat–Ae. biuncialis addition lines (2M^b, 3M^b, 7M^b, 3U^b and 5U^b) and on a wheat–Ae. geniculata (1U^g, 2U^g, 3U^g, 4U^g, 5U^g, 7U^g, 1M^g, 2M^g, 4M^g, 5M^g, 6M^g and 7M^g) addition series. Among the markers, 86 (79.6%) were amplified in the Ae. biuncialis genome. Compared with wheat, polymorphic bands of various lengths were detected on Ae. biuncialis for 35 (32.4%) of the wheat microsatellite markers. Three of these (8.6%) exhibited specific PCR products on wheat–Ae. biuncialis or wheat–Ae. geniculata addition lines. The primers GWM44 and GDM61 gave specific PCR products on the 2M^b and 3M^b wheat–Ae. biuncialis addition lines, but not on the 2M^g addition line of Ae. geniculata. A specific band was observed on the 7U^g wheat–Ae. geniculata addition line using the BARC184 primer. These three markers specific to the U and M genomes are helpful for the identification of 2M^b, 3M^b and 7U^g chromosome introgressions into wheat.     

Hybrid necrosis in wheat: evolutionary significance or potential barrier for gene flow?

One hundred and four released varieties of bread wheat (Triticum aestivum L ssp. aestivum) in India were crossed to two T. aestivum L ssp. aestivum testers, namely, C306 (Ne ₁ Ne ₁ ne ₂ ne ₂ ) and HD2329 (ne ₁ ne ₁ Ne ₂ Ne ₂ ) to determine the frequency and distribution of genes for hybrid necrosis present in them. Sixty-seven varieties (65.4 %) showed the presence of Ne ₂ gene and only eight varieties (7.7 %) had Ne ₁ gene in their background. Twenty-nine varieties (27.9 %) were non carrier (ne ₁ ne ₁ ne ₂ ne ₂ ) for both the genes. Most of the Ne ₁-carriers are of Indian origin and their pedigree revealed the involvement of landraces and old varieties as parents. Predominance of Ne ₂ gene in Indian varieties happened after the introduction of semi-dwarf Mexican wheat varieties, which are mostly Ne ₂ carriers and also due to the extensive and continuous use of germplasm from Mexican and European origin in the hybridization programme. Moreover varieties with Ne ₂ gene is selected for their linked beneficial traits mainly rust resistance genes. The phenomenon of hybrid necrosis is one among the post zygotic barrier speciation process which acts as a barrier for either intra or inter specific gene flow. The genetic architecture of hybrid necrosis in wheat is simple following the minimal predictions of the Bateson–Dobzhansky–Muller model. Widespread occurrence of dominant genes for hybrid necrosis in Indian varieties is of great concern to wheat breeders as it often interferes in the choice of elite parents and imposes restrictions on the productivity of crosses.     

Electrophoretic variation among and within strains of ‘kharkof’ wheat maintained at 11 locations

Summary The hard red winter wheat (Triticum aestivum L.) cultivar Kharkof was introduced to the United States at the turn of the century and has been included as the long-term check for the Southern and Northern Regional Performance Nurseries since 1930. Seed of Kharkof is typically maintained at each site at which the nurseries are grown. We obtained samples of Kharkof from 10 sites and the USDA Small Grains Collection in Beltsville, MD. Up to 54 individual kernels per strain were ground and evaluated for gliadin electrophoretic patterns. Strains from Beltsville, MD and Aberdeen, ID were completely uniform for gliadin patterns; they differed from each other and from all other strains. Seven strains were highly polymorphic, with 7 to 14 gliadin patterns occurring in each. However, there were large differences in pattern frequencies among strains, with the Ft. Collins, CO and Columbia, MO strains at one extreme, the Manhattan, KS and Lincoln, NE strains at the other, and the St. Paul, MN; York, NE; and Clovis, NM strains intermediate. Strains from Dallas and Chillicothe, TX were completely uniform for a pattern that also occurred in all of the polymorphic strains. The two Texas strains also had esterase and -amylase isoelectric focusing patterns different from the others, and the Beltsville strain had a different -amylase pattern. We concluded that the strains from Beltsville and Aberdeen were not Kharkof, that the Texas strains were derived from a single-plant selection out of Kharkof, and that the remaining strans have diverged through natural selection possibly operating in conjunction with genetic drift, outcrossing, and seed mixtures.     

Utilization of alien genes to enhance Fusarium head blight resistance in wheat – A review

Fusarium head blight (FHB) is a destructive disease of wheat worldwide. Sources of resistance to FHB are limited in wheat. Search for novel sources of effective resistance to this disease has been an urgent need in wheat breeding. Fusarium head blight resistance has been identified in relatives of wheat. Alien chromatin carrying FHB resistance genes has been incorporated into wheat through chromosome addition, substitution, and translocation. Relatives of wheat demonstrate a great potential to enhance resistance of wheat to FHB.