Metaphase-I analysis of a Triticum aestivum x T. monococcum hybrid by the C-banding technique

Summary The meiotic pairing behaviour at metaphase I of a Triticum aestivum×Triticum monococcum hybrid has been studied by means of the C-banding technique to ascertain the homology between the chromosomes in the A genome of the two species. The technique allowed the A and B genome chromosomes and the 2D, 3D and 5D chromosomes to be identified. Differences in the level of chromosome pairing in the A genome were noted. The T. monococcum 4A chromosome did not pair with any of the T. aestivum chromosomes in any of the metaphase I cells analysed. Two reciprocal translocations between the 2B and 2D chromosomes on one side and the 2A and 3D on the other side have been identified. The usefulness of the C-banding technique in the study of chromosome homology among species related to wheat is discussed.     

Physiological aspects of domestication in diploid wheat

Summary A comparative study of photosynthetic response to water stress was conducted with one genotype of wild einkorn (Triticum boeoticum, W) and one of domesticated einkorn (T. monococcum, C).Per unit leaf area, W showed a better performance for photosynthetic and transpiration activities, even under dry air and dry soil conditions. Its leaf water potential was always higher than that of C at any level of soil water potential. The difference in photosynthetic recovery from severe drought between W and C was also obvious. The photosynthetic rate, transpiration rate and water status of the leaves observed at 20 h after rewatering was almost the same as non-stressed leaves in W, whereas in C the photosynthetic rate was about half that of the non-stressed leaves, which was accompanied with a low transpiration rate and a high gas diffusion resistance. The ability of W to maintain a proper water balance over a wide range of soil water potential and to recover rapidly from severe drought seems to be a result of adaptation to its hard habitats.However, under favourable water supply, the photosynthetic rate per unit leaf nitrogen was higher in C than in W. This may be advantageous to bring about a better plant growth than W on the arable land where the improved water supply is guaranteed.     

Detection of repeated genotypes among 93 diploid wheat accessions

Summary An objective procedure was developed to find and eliminate repeated genotypes from a set of crop cultivars or accessions which may be used as parents for future plant breeding programs. Nonhierarchical, nonexclusive, exhaustive cluster analysis was used to group 93 diploid wheat accessions using LSD multiple comparisons of accession means based on data measured on seven characters. Beginning with the rarest accessions, i.e. those represented in the fewest clusters resulting from the clusters analysis, a minimum number of the accessions were chosen to represent the phenotypes of all 93 of the accessions. Two analyses were performed, one using data from an irrigated trial, the other from a dryland trial. The dryland trial data was more discriminating in that it required 71 accessions to represent all of the clusters generated from the original 93 accessions while the irrigated trial data required only 60 of the 93 accessions. In addition to the 71 accessions chosen from the dryland trial analysis, the irrigated trial analysis suggested an additional 12 accessions were phenotypically and, therefore, genotypically unique. The total of 83 unique accessions left 10 phenotypically duplicate accessions to be eliminated from the set of potential parents. Four of the 10 duplicated accessions were rare in that they were represented in very few clusters in either the irrigated trial analysis or in the dryland trial analysis. Because their phenotypes were not unique in spite of being rare, we believe such accessions were duplicated genotypically as well as phenotypically. The other six duplicates were common in that they were represented in a large number of clusters. Such accessions may not prove to be duplicates if grown in additional environments (trials), or if measured on additional characters.     

Pre-emptive breeding to control wheat rusts

Summary Pre-emptive or anticipatory breeding for resistance is breeding for resistance to future pathotypes. It is assumed that these will be derivatives of currently frequent pathotypes that need to mutate with respect to single host resistance genes in order to attack widely-grown cultivars. Success in this approach depends on relevant knowledge of the pathogenicity phenotypes and host resistance genes that occur throughout the wheat-growing areas. Because durability of resistance cannot be assumed, resistance breeding strategies are usually supported with the maintenance of genetic diversity to provide buffering against extreme crop losses in the event of significant pathogenic changes.     

Vernalization response and earliness per se in cultivars representing different eras of wheat breeding in Argentina

Argentine wheat cultivars are assumed to be essentially vernalization insensitive or very slightly sensitive. However, there are only speculations on this lack of vernalization requirement and a greater unawareness on the variation in earliness per se. The aims of this research have been to determine the extent of variability in vernalization requirement and earliness per se, and how the variability in both traits was produced by breeding programs, through the release of wheat cultivars from the 1930's to the 1990's in Argentina. Sixty-eight cultivars, selected among those of highest performance in each era, were evaluated under field and glasshouse conditions for their vernalization response and earliness per se. Forty per cent of the cultivars showed some vernalization response. There was a decrease in this requirement along the first decades of the analysed breeding period, likely in response to the considerable introgression of CIMMYT germplasm. This initial trend to release earlier cultivars was also evidenced in a clear decrease in earliness per se. As this tendency in both characteristics was reverted during the last two decades, it may denote that certain vernalization response and not extreme earliness per se, may contribute to achieve higher yield cultivars in our area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on multilines in wheat (Triticum aestivum L.).12. Breeding of a multiline variety by convergence of breeding lines

Summary The variation among the component lines of the KSML 3 (a multiline based on cultivar Kalyansona, spring bread wheat) was studied for agronomic characteristics. For days to earing and plant height the variation was small. This helped in imparting uniformity to the multiline. The lines had an improved tillering ability and had larger seeds. This partially explained the increased yield potential of the multiline as compared with Kalyansona.All the lines were susceptible only to one or two races of the yellow and brown rust. In no case any race was virulent against all the lines. In the field all the lines were resistant to both rusts.     

History of wheat breeding for a half century in Japan

Summary Wheat breeding efforts for a half century in Japan were investigated by using of 129 varieties registered in MAFF from 1929 to 1984 in the view point of case history for three years. Varieties released in each breeding station are classified apparently by growth habit associated closely with duration of the cold requirement. Heading date is earlier in varieties released in southwest breeding stations (southern varieties) than in varieties released in northern breeding stations (northern varieties). Culm length is higher and the pre-harvest sprouting is more sensitive in northern varieties. In quality characters, northern varieties has the higher milling rate, lower apparent amylose content and larger particle size of flour. In varieties released in the Tohoku district, trend of breeding direction with time is smaller ear numbers and larger 1,000-grain weight and greater resistance to powdery mildew. In varieties released in the Kyushu district, a significant correlation with released year was clearly observed with regard to early maturity, short culm length, less grain crude protein content, less apparent amylose content and higher milling rate on breeding advancement.     

Genetics of morphological traits in wild wheat,Triticum turgidum var.dicoccoides

Summary The mode of inheritance, linkage groups, and chromosomal location of 23 morphological and 4 biochemical traits were characterized in the wild tetraploid emmer wheat,Triticum turgidum var.dicoccoides. These traits were described and their mode of inheritance was determined by their segregation in four F₂ populations derived from crosses between four var.dicoccoides accessions and a tetraploiddurum cultivar. Linkage groups among the genes encoding for these traits were determined or postulated, and their chromosomal location was deduced by linkage to previously located genes. The genetic control of the following traits was characterized and is first reported here: black keel; hairy leaf sheath; hairy auricles; hairy rachilla; hairy kernel brush; obtuse flag leaf; and curved neck/peduncle. The linkage data indicated that developmentally-related genes tended to occur in clusters.     

Patterns of RFLP-based genetic diversity in germplasm pools of common wheat with different geographical or breeding program origins

A set of 292 accessions of common wheat (Triticum aestivum L.) representing 21 germplasm pools based on geographical or breeding program origins was assayed for RFLP diversity. Thirty cDNA and genomic DNA probes and the HindIII restriction enzyme were employed for RFLP analysis. About 61% of all 233 scored bands were present in 75% or more of the accessions. All but one of the 30 probes revealed polymorphism, and the average number of distinct patterns per probe over all accessions was 9.5.Polymorphic Information Content (PIC) values within a pool varied from 0 to 0.9 and depended on the identities of both the germplasm pool and the probe. Rare banding patterns with a relative frequency of ≤0.2 within a pool were detected. These rare patterns were more likely to occur in pools exhibiting high levels of heterogeneity. The highest level of polymorphism was observed in the Turkish landraces from Southwest Asia. The Eastern U.S. soft red winter wheat germplasm pool was more genetically diverse than the other advanced germplasm pools, and nearly as diverse as the Turkish landrace pool. RFLP-based genetic relationships between germplasm pools generally tracked expectations based on common geographical origin, breeding history and/or shared parentages. The Chinese wheat landraces from Sichuan, Tibet, and Yunnan provinces were distinct from other pools. Similarity matrices for among-pool genetic distance estimates based on either band frequencies or banding pattern frequencies showed good correlation with matrices derived from Nei and Li's mean genetic similarity estimates (r=−0.82^** and r=−0.73^**, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Prehaustorial resistance to the wheat leaf rust fungus, Puccinia triticina, in Triticum monococcum (s.s.)

Diploid wheat, Triticum monococcum s.l., is a host for the wheat leaf rust fungus, Puccinia triticina. Some accessions have been reported to show a high degree of prehaustorial resistance. This is non-hypersensitivity resistance, which acts before the formation of haustoria by the pathogen. To assess the frequency of prehaustorial resistance 598 accessions of diploid wheat were inoculated with the wheat leaf rust isolate Felix. Most T. monococcum s.s. accessions (84%) were resistant whereas all T. urartu and all but three T. boeoticumaccessions were susceptible. Histological components analysis revealed that a high percentage of prehaustorial resistance to P. triticina was found in only three T. monococcum accessions. No haustoria were observed in such infection units confirming the prehaustorial nature of the resistance. Prehaustorial abortion of certain infection units in an accession always coincided with posthaustorial abortion of the other infection units. This revised version was published online in July 2006 with corrections to the Cover Date.     

Relationship between common wheat (Triticum aestivum L.) gluten proteins and dough rheological properties

This paper reports the correlation between the rheological properties of bread wheat dough and the types and quantities of endosperm proteins in 28 common wheat cultivars. Different methods were used to analyse the allelic composition of these cultivars and the relative quantities of the different proteins contributing to the gluten structure. Neither dough strength (W) nor tenacity/extensibility (P/L) correlated with allelic composition. Different wheats with the same allelic composition (i.e., with respect to glutenins) showed different rheological properties. The glutenins were the most influential components of W and P/L, especially the high molecular weight (HMW) glutenin subunits and in particular the type x form. These proteins seem to increase W and are the main constituents of the gluten network. The gliadins and low molecular weight (LMW) glutenin subunits appear to act as a “solvent”, and thus modify the rheological properties of the dough by either interfering with the polymerisation of the HMW glutenin subunits, or by altering the relative amounts of the different types of glutenin available. Thus, the protein subunits coded for by the alleles Glu-B1x7 and Glu-D1x5 stabilised the gluten network, whereas those coded for by Glu-B1x17 and Glu-D1x2 had the opposite effect. Dough properties therefore appear to depend on the glutenin/gliadins balance, and on the ratio of the type x and type y HMW proteins. The influence of external factors seems to depend on the allelic composition of each cultivar.     

C-band polymorphism and structural rearrangements detected in common wheat (Triticum aestivum)

Summary Giemsa C-banding allows for the identification of all 21 chromosome pairs of hexaploid wheat. However, variation in banding patterns of individual chromosomes and structural rearrangements exist between different cultivars making chromosome identification more difficult. The paper summarizes the available data on C-band polymorphism and structural rearrangement present in wheat cultivars and germplasms.     

Inheritance of cleistogamic flowering in durum wheat (Triticum durum)

Summary Generally durum wheat flowers are chasmogamous but very rarely, cleistogamy may be observed. Genetic studies based on six crosses and back crosses showed that chasmogamy was determined by a single dominant gene Cl, plants homozygous for the recessive allele, cl, were cleistogamous. The flowering behaviour phenotypes were unaffected by environmental conditions. Cleistogamy was attributed to poorly developed lodicules and stiff perianth.     

Boron deficiency induced male sterility in wheat (Triticum aestivum L.) and implications for plant breeding

Boron (B) deficiency causes grain set in wheat to fail. A wide range of genotypic variation in the response to low B has been observed. Genotypes were screened in low B in soil and sand culture, and classified into five groups, namely, very sensitive, sensitive, moderately sensitive, moderately tolerant and tolerant. At very low levels of B, the very sensitive to sensitive genotypes were completely male sterile and set only a few or no grain, while the tolerant genotypes set grain normally. Natural outcrossing was detected in these male sterile plants when a tolerant genotype was growing nearby. Grain set by cross fertilisation was markedly enhanced by a B application directly on the ear of the male sterile plants. Three practical implications are suggested. Firstly, genotypes that are tolerant to low B can provide a solution for grain set failure caused by B deficiency. Secondly, the potential for outcrossing in male sterile B deficient wheat has to be taken into account in the maintenance of pure lines in low B soils even though wheat is normally self pollinated. Thirdly, a simple and novel method for hybridization is suggested, in which B deficiency is used as fertility selective medium and male sterile female parents and fertile male parents are provided by genotypic variation in the response to low B. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heterosis of grain weight in wheat hybrids with Triticum timopheevi cytoplasm

Summary Two kinds of wheat hybrids with the same nuclear genotype but different cytoplasms (one with T.timopheevi cytoplasm, i.e., A/R, and the other with T.aestivum cytoplasm, i.e., B/R) were produced by two 3 × 5 incomplete diallel crosses of 3 A-lines, 3 corresponding B-lines and 5 R-lines, respectively. Experimental results did not show significant differences between the hybrids of A/R and B/R in grain filling characteristics and grain weight. The beterosis of grain weight seems mainly determined by the nuclear genotype. Although the seeds set on most A-lines were shrivelled, such a phenomenon was not found in grains set on F₁. The duration of the lag period (D₁) and the average grain filling rates during the linear period and the mature period (i.e., FR₂ and FR₃) were significantly and positively related to 1000-grain weight. It was in these factors that most hybrids displayed clear mid-parent (MP) heterosis. The amount of grain weight heterosis was not significantly related to MP value. This indicates that the grain weight heterosis of wheat hybrids will not decrease with an increase of the MP value.     

Inheritance,heritability and breeding behaviour of three sources of resistance to Septoria tritici in wheat

Summary We examined the inheritance, heritability, and breeding behaviour of resistance to Septoria tritict in the spring wheat cultivars Seabreeze, Veranopolis, and IAS-20 in crosses to the susceptible Australian spring cultivar Gamenya. Resistance in Seabreeze was higher than that in Veranopolis and IAS-20. Inheritance of resistance in Seabreeze seems to be determined by at least three recessive genes. Resistance in Veranopolis and IAS-20 might be due to a single gene. Similarity of inheritance patterns and breeding behaviour of the resistance from Veranopolis and IAS-20 and the common ancestry of these two cultivars suggest that they may carry the same gene. Standard unit heritabilities of Septoria scores, as measured by correlation of F₂ plant with F₃ family mean data, were high (57–68%). Parent offspring genetic correlations confirmed previously reported associations between resistance and lateness and resistance and tall plant height, but correlations were not sufficiently high to be a major obstacle to selection. Resistance in Veranopolis and IAS-20 were easily recovered in first backcrosses while that in Sea breeze was more difficult to recover.Contribution from the Department of Agriculture Western Australia.     

Efficient application of in vitro anther culture for different European winter wheat (Triticum aestivum L.) breeding programmes

The efficiency of our anther culture protocol was tested with high‐ and low‐responding genotypes, ‘Svilena’ and ‘Berengar’, and 93 F₁ winter wheat crosses in 2010 and 2011. Based on data for these genotypes, the effect of genotype influenced the number of embryo‐like structures, regenerated plantlets and green plantlets, while the number of albino plantlets was affected by genotype, year and environmental factors. Although genotype also influenced the production of green plantlets from breeding crosses, with green plantlets per 100 anthers ranging from 0.04 to 28.67, the average regeneration rate over all crosses was 5.3 green plantlets/100 anthers, which resulted in a total of 11 416 well‐rooted green plantlets. The survival rate of green plantlets following acclimatization was 97.21% in 2010 and 96.34% in 2011. In this study, the phenomenon of albinism and genotype dependency did not hinder the production of more than five thousand green plantlets each year. In our experiments, anther culture proved to be an efficient method in winter wheat breeding programmes with lower costs than alternative technologies.     

Selection for yield in wheat breeding

Summary If selection based on F₃ yield tests is to be effective, the yield tests must be successful in discriminating among yield genotypes. The available literature indicates that simple tests with limited or no replication are not very effective, although more extensive, replicated tests may be.Data from an experiment comparing F₃ yield tests with a single seed descent procedure showed that F₃ selection based on a two-replicate test with single seed descent procedure did not justify the extra work involved.     

Physiological studies on grass-dwarf selection lines in wheat (Triticum aestivum L.)

Summary Low power heating wires insulated in a flexible plastic strip were used to heat the shoot meristematic region of grass-dwarf genotypes to a precise temperature. The results indicate that the shoot apical meristem is the region requiring 26°C for the initiation of reproductive development in these genotypes. A secondary effect of the reproductive growth induced by high temperature treatments, was a reduction in the high levels of peroxidase enzymes found in vegetative grass-dwarf plants. The heating wire provides a precise method to identify Type I, II and III grass-dwarf genotypes according to their temperature requirements, of 26°C, 21°C and 16°C respectively, for reproductive growth under the same temperature (16 C) and photoperiod (12 hours).     

Evaluation of three sources of pollen fertility restoration genes and natural outcrossing of cytoplasmic male-sterile wheat

Summary Fertility restoration genes in Triticum aestivum L. in Texas Restorer Composite (TRC), D6301, and four CIMMYT restorer lines were studied, and selection was made for higher fertility in TRC. Mean-while, outcrossing percentages of seed set for 27 spring habit cytoplasmic male sterile (cms) varieties were evaluated for 3 to 5 years at Davis. The winter-habit TRC material did not restore reasonably good fertility, and the response to selection for higher fertility seemed to be slow. This poor fertility could be partly due to its late winter growth habit causing flowering at a period of high temperature and low humidity at Davis. The highest F₁ fertility was 46.6% in the cross cms Ramona x TRC-6, and its F₂ segregated into the ratio of 15 fertile to 1 sterile, with fertility ranging from 3.2 to 100%. Suggested for its improvement was intensive selection in the original TRC material and in the segre-gating F₂ population, followed by intercrossing. D6301 has 2 fertility restoration genes with different strengths which restore fertility up to 45.2% when both genes are heterozygous. D6301 is quite likely heterogeneous for these genes. Four CIMMYT restorer lines, D7464, D7465, D7466, and D7467, had satisfactory F₁ fertility restoration after crossing with cms Ramona 50. In 1975, the fertilities of the F₁'s ranged from 71 to 85% and were over 90% in 1976. The F₂ population of the cross cms Ramona 50 × D7464 segregated into a ratio of 3 fertile to 1 sterile, indicating that D7464 has a single dominant gene for fertility restoration. The F₂'s of crosses cms Ramona 50 × D7465, cms Ramona 50 × D7466, and cms Ramona 50 × D7467 gave a ratio of 15 fertile to 1 sterile, indicating that two gene pairs in these three lines were responsible for the fertility restoration. The best of this group was D7467 which restored fertility fully after being crossed with cms Ramona 50 (T. timopheevi cytoplasm).The early-flowering cms male-sterile varieties had higher outcrossing rates (16 to 38%) than late varieties (6 to 30%) over a 5-year period. This was due to hot and dry weather during the late growing season as well as to the rarity of windborne pollen. In 1970, 1971, 1972, and 1976, the variation among varieties was rather great. Some of them such as Roque 66 and Bajio 67, had consistently high outcrossing rates. This outcrossing ability seemed to be inherited and probably associated with the open-flowering characteristics of each variety.