Comparative genetic mapping of homoeologous genes for the chlorina phenotype in the genus <Emphasis Type="Italic">Triticum</Emphasis>

Triticum monococcum L. (2n = 2x = 14, A^mA^m genome) is one of the most ancient of the domesticated crops in the Middle East, but it is not the ancestor of the A genome of durum wheat (T. durum Desf. 2n = 4x = 28, genomes BBAA) and bread wheat (T. aestivum L., 2n = 6x = 42, genomes BBAADD). It has been suggested that some differentiation has occurred between the A^m and A genomes. The chlorina mutants at the cn-A1 locus located on chromosome 7AL have been described in T. aestivum L. and T. durum, and a chlorina mutant has been found in T. monococcum. The aims of our study were to establish linkage maps for chlorina mutant genes on chromosome 7A of T. aestivum and T. durum and chromosome 7A^m of T. monococcum and to discuss the differentiation that has occurred between the A and A^m genomes. The chlorina mutant gene was found to be linked with Xhbg234 (8.0 cM) and Xgwm282 (4.3 cM) in F₂ plants of T. aestivum ANK-32A/T. petropavlovskyi k54716, and with Xbarc192 (19.5 cM) and Xgwm282 (12.0 cM) in F₂ plants of T. durum ANW5A-7A/T. carthlicum #521. Both the hexaploid and tetraploid wheats contained a common marker, Xgwm282. In F₂ lines of T. monococcum KT 3-21/T. sinskajae, the cn-A1 locus was bracketed by Xgwm748 (25.7 cM) and Xhbg412 (30.8 cM) on chromosome 7A^mL. The distal markers, Xhbg412, Xgwm282, and Xgwm332, were tightly linked in T. aestivum and T. durum. The common marker Xhbg412 indicated that the chlorina mutant genes are located on chromosome 7AL and that they are homoeologous mutations.     

Genetic necrosis in Triticum × aegilops pentaploid hybrids

Summary Ten varieties of Triticum aestivum and three synthetic T. durum + Aegilops squarrosa hexaploids were crossed with an Ae. bicornis + Ae. squarrosa amphiploid. 55 hybrid plants involving 9 different combinations developed necrosis and died before maturity. The two plants which survived were both from the F₁ with a synthetic hexaploid, T. durum var. Carleton + Ae. squarrosa.The genetic necrosis developing in these hybrids differed from hybrid necrosis and red hybrid chlorosis both in symptoms and in the genetic basis. The symptoms were similar to those reported for a number of Triticum x Aegilops hybrids in which Ae. bicornis and Ae. squarrosa were involved but the genetic basis was not determined. The survival of 2 of the 13 progenies from one cross is discussed.

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Host plant resistance in some wild wheats to the Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae)

A total of 259 accessions of wild Triticum species originating from different countries, along with 91 triticale (6×)× bread wheat true-breeding derivatives, two bread wheat, and three triticale cultivars were screened for resistance to the Russian wheat aphid, a serious insect pest of the wheat crop. Twenty-four entries with low damage ratings on the basis of amount of leaf rolling and leaf chlorosis were retested along with resistant and susceptible controls. On the basis of leaf roll damage ratings, eight entries including four Triticum monococcum var. boeoticum (T. boeoticum), one T. monococcum var. monococcum (T. monococcum), two T. timopheevii var. araraticum (T. araraticum), and one triticale cultivar were significantly superior to ‘Karl’ (susceptible control) wheat. Among these, four accessions — three T. boeoticum and one T. araraticum— were significantly superior to all other entries and were equal to the resistant control (PI 372129) in resistance rating based on leaf rolling and leaf chlorosis (except T. boeoticum TA 202). The leaf chlorosis damage rating of all accessions were significantly lower than that of the susceptible check.     

Reproductive Behavior of Hexaploid/Diploid Wheat Hybrids 1

The bottleneck restricting introgression of useful genes directly from diploid into hexaploid wheats is the low number of BC₁F₁ seeds obtained. In crosses between hexaploid wheat (Triticum aestivum L.; AABBDD) and Aegilops squarrosa L. (DD) or T. urartu Thum. (AA), this bottleneck may be overcome simply by pollinating a sufficient number of F₁ spikes. However, hybrids between hexaploid wheat cultivars (T. aestivum) and T. monococcum L. (AA) generally are highly female-sterile, often having no pistils. One T. monococcum accession, PI 355520, when crossed with T. aestivum, produced hybrids with female fertility in the same range as that of T. aestivum/A. squarrosa or T. aestivum/T. urartu hybrids, ca. 0.5 to 1.0 backcross seed per spike. We found that female fertility was controlled by two duplicate genes in PI 355520, and that this accession can be used as a bridging parent to introgress genes from other T. monococcum accessions into hexaploid wheat. Pairing of homologous chromosomes was less frequent and weaker in such crosses than in T. aestivum/A. squarrosa crosses, but homoeologous bivalents occurred at a rate of almost 0.5 II per cell. Restitution division was detected in crosses involving all three diploid species and was confirmed cytologically in crosses with PI 355520. Chromosome numbers of BC₁F₁ plants ranged from 35 to 67; plants with 49 or more chromosomes occurred at frequencies of 0.09 to 0.21 among progeny of A. squarrosa and T. urartu and 0.29 in progeny of T. aestivum/T. monococcum crosses involving PI 355520. These results are consistent with those of previous studies, demonstrating the potential of direct Hexaploid/diploid crosses for rapidly introgressing useful genes into Hexaploid wheat with minimum disturbance of the background genotype.     

Resistance to Septoria nodorum blotch in several Triticum species

Summary Resistance to septoria nodorum blotch in Triticum monococcum, T. tauschii, T. timopheevii, T. dicoccum and T. durum was evaluated on plants at the three-leaf stage in greenhouse tests. A high frequency of resistant genotypes was found in T. monococcum, T. tauschii and T. timopheevii, but not in T. dicoccum and T. durum. The resistance of F₁ plants of crosses of resistant T. monococcum (PI 289599) and T. timopheevii (PI 290518) accessions with susceptible common wheat cv. Park and durum wheat cv. Wakooma, respectively, was evaluated on the basis of percentage leaf necrosis, lesion number, lesion size and incubation period. No dominance was found for long incubation period, but various dominance relationships occurred for low percentage leaf necrosis, low lesion number and small lesion size, depending on the cross. Multiple regression analysis showed that lesion number contributed more to percentage leaf necrosis than lesion size or incubation period. Resistance to septoria nodorum blotch was transferred successfully from T. timopheevii to cultivated durum wheat. Resistant BC₁F₇ lines, recovered from the T. timopheevii (PI 290518) × Wakooma cross, showed normal chromosome behaviour at meiosis (14 bivalents) and were self-fertile. However, an effective level of resistance was not recovered in lines derived from the other interspecific crosses.     

Mapping genes controlling anthocyanin pigmentation on the glume and pericarp in tetraploid wheat (<Emphasis Type="Italic">Triticum durum</Emphasis> L.)

A novel gene, designated Pg (purple glume), controlling anthocyanin pigmentation of the glume was identified and mapped in an F₂ population from the durum wheat (Triticum durum) cross TRI 15744/TRI 2719. This gene was close to one of the two complementary dominant genes, controlling anthocyanin pigmentation of the pericarp (gene Pp3) in the centromere region of chromosome 2A; the other Pp gene (Pp1) was mapped on the short arm of chromosome 7B, near gene Pc controlling anthocyanin pigmentation of the culm and co-segregating with Pls (purple leaf sheath) and Plb (purple leaf blade). On the basis of the mapping results, the Pp3, Pc, Pls and Plb genes of T. durum were regarded as allelic to the T. aestivum Pp3, Pc-B1, Pls-B1 and Plb-B1 loci. The likely allelism of Pp1 in T. durum and T. aestivum remains in dispute, the present durum Pp gene mapped to the short arm of chromosome 7B, whereas in common wheat it was reportedly located on the long arm.     

Cytoplasmic and cytogenetic relationships among tetraploid Triticum species

Summary The F₁ hybrids from crosses of 59 accessions of wild and cultivated Triticum types including amphidiploids T. boeoticum-Ae. squarrosa, T. timopheevi-Ae. squarrosa, T. timopheevi-T. monococcum, T. boeoticum (4n), T. macha, and T. Zhukovskyi with T. durum Sel. 56-1 and/or T. aestivum were examined for male sterility and chromosome pairing at metaphase I of meiosis in pollen mother cells. Those hybrids which produced male-sterile F₁'s were recurrently backrossed with pollen from T. durum or T. aestivum to study segregation for male sterility and/or to confirm cytoplasmic male sterility.All T. timopheevi and T. araraticum accessions and several T. dicoccoides types, including T. dicoccoides var. nudiglumis from the Turkey-Iran-Iraq area, had male sterility inducing cytoplasm. The chromosome pairing in the F₁ hybrids indicated that all tetraploid Triticum accessions with male sterility inducing cytoplasm had genome AAGG. T. dicoccoides Körn types from the Turkey-Iran-Iraq area had genomes AABB and did not have male sterility inducing cytoplasm. Therefore, T. dicoccoides Körn and the T. timopheevi complex differ from each other cytoplasmically and cytogenetically and occur sympatrically in the Turkey-Iran-Iraq area.Possibly, the cytoplasm of the emmers was not derived from the putative diploid progenitors, T. boeoticum, Ae. speltoides, or Ae. bicornis as indicated by their nucleo-cytoplasmic and cytogenetic relationships with the tetraploid Triticum species. The cytoplasmic differences among Ae. speltoides, T. araraticum and T. timopheevi are of a relatively smaller magnitude than the cytoplasmic differences among T. timopheevi, T. boeoticum, and the emmers. A complete analysis of nucleo-cytoplasmic relationships among Triticum and Aegilops species may indicate the cytoplasmic donor(s) to the two tetraploid Triticum species complexes.Authorized for publication 19 July, 1972 as Paper No 397 in the Journal Series of the North Dakota Agricultural Experiment Stations.     

Transfer of stem rust seedling resistance from wild diploid einkorn to tetraploid durum wheat by means of a triploid hybrid bridge

Summary Transfer of stem rust resistance from diploid wild einkorn, Triticum boeoticum, to susceptible Mindum and Spelmar, varieties of cultivated T. durum, was achieved by means of a triploid hybrid bridge and subsequent backcrossing to the tetraploid parent. Seedlings of the second hybrid generation segregated for resistance to race 14 of Puccinia graminis f.sp. tritici which was used as test race in this investigation. The F₃ and F₄ progenies included segregants which displayed seedling resistance also to races 17, 19, 21, 40, 53, 194, 222, 315 and 322. Since these were the same races which proved avirulent to the T. boeoticum donor but virulent to the T. durum recipients, it was concluded that the full pattern of resistance determined in the wild diploid parent of this cross was transferred to the tetraploid durum-like hybrid derivatives.Joint contribution from The Volcani Institute of Agricultural Research, Bet Dagan, 1970 Series, No. 1801-E, the Tel Aviv University, and the Hebrew University of Jerusalem, Israel.     

Molecular mapping of cereal cyst nematode resistance in <Emphasis Type="Italic">Triticum monococcum</Emphasis> L. and its transfer to the genetic background of cultivated wheat

Triticum monococcum, the diploid A genome species, harbours enormous variability for resistance to biotic stresses. A spring type T. monococcum acc. 14087 was found to be resistant to Heterodera avenae (cereal cyst nematode, CCN). A recombinant inbred line population (RIL) developed by crossing this accession with a CCN susceptible T. boeoticum acc. 5088 was used for studying the inheritance and map location of the CCN resistance. Based on composite interval mapping two QTL, one each on chromosome 1AS and 2AS, were detected. The QTL on 1A, designated as Qcre.pau-1A, appeared to be a major gene with 26% contribution to the overall phenotypic variance whereas the QTL on 2A designated as Qcre.pau-2A contributed 13% to total phenotypic variation. Qcre.pau-1A is novel, being the only CCN resistance gene mapped in any ‘A’ genome species and none of the other known genes have been mapped on chromosome 1A. The QTL Qcre.pau-2A might be allelic to Cre5, a CCN resistance gene transferred from Ae. ventricosa and mapped on 2AS. The Qcre.pau-1A was transferred to cultivated wheat using T. durum cv. PBW114 as the bridging species. Selected CCN resistant F₈ lines showed introgression for the molecular markers identified to be linked with CCN resistance locus Qcre.pau-1A. Thus, this gene alone could impart complete resistance against CCN. These introgression lines can be used for marker-assisted transfer of Qcre.pau-1A to elite wheat cultivars.     

Waxy proteins in diploid, tetraploid and hexaploid wheats

Electrophoretic analyses of waxy proteins, encoded by genes present at the Wx‐1 loci, present in several cultivars and accessions of hexaploid wheat, Triticum aestivum, have permitted the detection of null alleles at the Wx‐B1 and Wx‐D1 loci. Polymorphism at the Wx‐A1 and Wx‐B1 loci was also investigated in several accessions of tetraploid wheats, Triticum durum, Triticum dicoccoides and Triticum timopheevi, and in diploid species, Triticum urartu, Triticum boeoticum and Triticum monococcum. One null allele at the Wx‐A1 locus and three polymorphic alleles at Wx‐B1 locus were detected in T. durum; a new allele at one of the two waxy loci was identified in the tetraploid wheat T. timopheevi; no polymorphism was detected in diploid species. Polymerase chain reaction techniques made possible the detection of further polymorphism existing at the Wx‐1 loci and the reason for the lack of expression of the null genotypes to be investigated. The null forms detected at each locus have been used to produce complete sets of partial and total waxy lines in durum and bread wheat.     

Agronomical performance and breeding value of selected strains of diploid wheat,Triticum monococcum

Summary Twenty-one germplasm accessions and breeding lines of einkorn wheat (Triticum monococcum ssp. monococcum and ssp. sinskajae) were grown at two sites in Italy and evaluated for various field and seed characteristics. Grain yields of germplasm accessions were relatively high (317–3238 kg/ha), but distinctly lower than those of four modern cultivars of tetraploid (T. turgidum ssp. durum) and hexaploid wheat (T. aestivum ssp. Aestivum) included in the experiments as controls. As expected, all Einkorns-including some substantially higher yielding crossbred lines (3415–4362 kg/ha)-were defective for one or more agronomically relevant features. However, a few of the accessions examined were found to contain, as a group, practically all the genes needed to breed monococcums having the main field attributes of a modern wheat cultivar: high yielding capacity, good threshability, large kernel size, earliness, short stature and adequate lodging resistance. Still higher yielding diploid wheats, more responsive to improved growing conditions and of better seed quality, could probably be obtained from crosses with wild monococcums bearing mostly two-seeded florets and with accessions producing less slender-shaped kernels. Some of the Einkorns examined were found to carry minor genes for easy threshing which might enhance the efficacy of the major gene for soft glumes carried by T. monococcum ssp. sinskajae, a partially free-threshing diploid wheat taxon. Seed protein percentage of monococcums was markedly higher than that of durum and bread wheat cultivars even in those cases where their grain yields surpassed those of the polyploid checks. The possibilities offered by diploid wheat in the exploitation of novel endosperm mutants and F₁ hybrid vigour, as well as in the fields of celiac disease, crop diversification and resistance to agro-biological stresses are discussed. Breeding priorities and strategies are also proposed.     

Sources of resistance to Mayetiola Destructor in breadwheat and durum wheat in Morocco

Summary Grain yield reductions of both breadwheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. durum) caused by attacks of Hessian fly (Mayetiola destructor Say) are second perhaps only to those caused by inadequate soil moisture in Morocco. To identify effective sources of resistance, 817 entries of common wheat and durum wheat reported to be resistant to Hessian fly were evaluated under natural infestations in Morocco. A large number of genes conferring virulence are present in populations of Moroccan Mayetiola. The genes H₁, H₂, H₃, h₄, H₆, H₇, H₈, H₉, H₁₀, H₁₁, H₁₄, H₁₅, and H₁₆ as well as the Marquillo, Kawvale and PI 94587 resistance sources are not useful for cereal improvement in North Africa. Luso, which has the gene H₁₂, also appeared susceptible in limited testing. Genotypes having the genes H₅ and H₁₃ were identified as significantly reducing larval survial in natural populations of Mayetiola. Of 11 resistant breadwheats identified with unknown genes, seven were from Portugal and three were from the Soviet Union. Although none of the durums tested had high levels of reistance, the two most promising durums were from Portugal. It is proposed that initially H₅ be deployed in durum wheats and H₁₃ be used in common wheat improvement. Leaf pubescence appears of little use in reducing the larval survival of Mayetiola.     

A sequence-specific PCR marker linked with Pm21 distinguishes chromosomes 6AS, 6BS, 6DS of Triticum aestivum and 6VS of Haynaldia villosa

To develop markers linked with Pm21 located on chromosome 6VS of Haynaldia villosa, a pair of primers (NAU/xibao15F and NAU/xibao15R) were designed according to the sequence of a serine/threonine kinase gene (Contig17515), whose expression was induced by Blumeria graminis and selected from the gene expression experiment using the Barley GeneChip. Using genomic DNA of various genetic stocks including the wheat variety ‘Yangmai#5’, H. villosa, Triticum durum–H. villosa amphiploid, seven T. aestivum–H. villosa addition lines involving chromosomes 1V–7V, the translocation line T6VS·6AL, and 21 nullisomic–tetrasomic and eight deletion lines of T. aestivum‘Chinese Spring’ as templates, four amplicons specific for 6VS, 6AS, 6BS and 6DS, respectively, were produced. F₂ individuals derived from the cross of ‘Yangmai#5’ × T6VS·6AL were analysed, and data indicate that NAU/xibao15₉₀₂ could be used as a co‐dominant marker for selecting Pm21 located on 6VS.     

Genetic variation for tolerance or resistance to barley yellow dwarf virus in durum wheat

Summary One durum wheat line (Triticum durum), cv. 82PCD476, with useful BYDV tolerance or resistance, was singled out of 5 152 lines evaluated between 1979 and 1986. A few other lines such as cv. Boohai and cv. 12th IDSN 227, slightly inferior to cv. 82PCD476, also showed some value. With an hybrid of cv. 12th IDSN227 with the susceptible cv. 84PCY-S531, broad-sense heritability values of 0.37–0.41 were obtained for symptoms and a heritability value of 0.55 was obtained for the total weight of spikes. The weight of spikes was considered as a good indicator of wheat tolerance to BYDV. Although BYDV resistance or tolerance genes are not very common in durum wheat, sources of heritable resistance could be found. However, the resistance ofT. aestivum to BYDV was superior to the one found inT. durum.Cintribution no. 323     

Somatic Embryogenesis and Plant Regeneration from Tritordeum

Regeneration of plants by somatic embryogenesis from immature embryos of hexaploid tritordeum (AABBH^chH^ch, amphiploid Hordeum chilense×Triticum turgidum conv. durum) and durum wheat (Triticum tergidum) was induced on MS medium supplemented with different 2.4-D concentrations. Well-defined embryoids were formed with a high frequency on the scutellar callus from 1 or 2 weeks onwards and plantlets were developed from them. In the best cases from one single explant more than 100 plants could be obtained. Plants were also regenerated by somatic embryogenesis from inflorescences of Hordeum chilense×Triticum turgiditm conv. durum hybrid and its respective hexa-amphiploid. With regard to callus induction and regenerative ability, evident differences between hexa- and octoploid (H. chilense×T. aestivum) tritordeum were found, the latter showing a very low response.     

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.     

Synthetic Amphiploids of Wheet as a ource of Resistance to Karnal Bunt (Neovossia Indica)

Twelve synthesized ainphiplonds involving Karnal bunt (Neovossia indica)-resisiant accessions of Triticum monococum, T. boeoticum and Aegilops sqiwrrosa and susceptible but otherwise well adapted and high yielding T. Durum cultiviars were evaluated for Karnal bunt resisiance under artificial inoculation conditions. All ihe synthetic amphiploids, except DWI. 5031 x T. monocoirtum aniphlploid, were free from Karnal bunt disease indicating that the Karnal bunt resistance or T. motsococcum, T. boeoticMrn and Ae, squarrosa is expressec in the presence of the dnrum complement. The importance and utilization of the amphiploids fox breeding wheat varieties resistant to karnal bunt are discussed.     

Metabolism, seedling growth and nucleolar activity in germinating diploid wheat Triticum monococcum ssp. monococcum cv. Einkorn

Seed germination, seedling growth, mitotic and nucleolar activity were investigated as indicators of metabolic activity in a diploid wheat, Triticum monococcum ssp. monococcum cv. Einkorn. Two developmental phases were identified, an initial lag phase during which reactivation of NOR's and the initiation of mitotic activity (10 h) took place prior to the appearance of the primary root (16 h). Dominance interactions were observed between the NOR's of chromosomes 1A and 5A with the NOR's of the one pair activated before the other and forming therefore larger nucleoli. The total number of nucleoli per 500 cells also varied according to the stages of the cell cycle over time. The mitotic activity had an initial exponential rise, but showed signs of flattening out after 10 h of mitosis with opposite levels of activity in the primary and first pair of lateral roots thereafter. Secondly, an exponential phase in root and shoot growth, mobilization of reserve food and respiration rate was observed during seedling growth. Comparisons were done on work from a previous investigation on two polyploid wheat accessions belonging toT. turgidum ssp. durum and T. aestivum species. T. monococcum displayed a higher embryo growth than the polyploids, that may be explained by having a lighter embryo and caryopsis weight that may influence the uptake of water and reactivation of metabolic activity. During the seedling growth period, the two polyploid species displayed a faster growth rate than the diploid probably due to the differences in the number of genomes, the hybrid nature of the polyploids and a more complex gene control in the polyploids. This revised version was published online in August 2006 with corrections to the Cover Date.     

The reduced height genes do not affect the root penetration ability in wheat

Root penetration (RP) ability into compacted soil is an important breeding target for drought avoidance by durum (Triticum turgidum L. var. durum) and bread wheat (T. aestivum L.) in regions with compacted soils and water deficits. However, it is said generally that yield of the current cultivars introduced the reduced height gene (Rht-B1b or Rht-D1b) are more sensitive to drought stress than that of old landraces. This study investigated the effect of the Rht genes on RP ability using the seedlings of near-isogenic lines (NILs) of Rht genes of LD222 durum wheat and April Bearded bread wheat, and 110 recombinant inbred lines (RILs) of durum wheat derived from the cross between the tall landrace (Jennah Khetifa; Rht-B1a Rht-B1a) and semi-dwarf cultivar (Cham1; Rht-B1b Rht-B1b). One seedling of each genotype was grown in a pot (6 cm diameter, 15 cm height) with a disc of 3 mm thickness made from paraffin and Vaseline mixture (PV) in 10 cm depth, as a substitute for a compacted soil layer. The RP index [number of roots penetrating through the PV disc per plant (PVRN)/total number of seminal and crown roots per plant (TRN)] was measured at eight weeks after sowing and used as the indicator of RP ability of seedling. In NILs, the shoot length decreased significantly because of the introduction of either Rht-B1b or Rht-D1b dwarfing genes, but the RP index was similar to those of tall parents. In RILs, although the RP index and shoot length were higher in Jennah Khetifa than in Cham1, the relationship between RP index and shoot length was not significant (r = 0.156). Both results indicate that RP ability of wheat does not link to dwarfness regulated by Rht genes. We suppose therefore that it would be possible to develop a high yielding semi-dwarf cultivar with excellent RP ability.