Preferential Transmission in Bread Wheat of a Chromosome Segment Derived from Thinopyrum distichum (Thunb.) Löve

A Thinopyrum distichum chromosome segment translocated on chromosome arm 7DL. of the line ‘Indis’, was shown to be preferentially transmitted in crosses with other bread wheats. The translocated segment carries a gene for leaf rust resistance and produces a null condition for the endopeptidase product, EP-Dla. These characters were used to follow the transmission of the translocated chromosome in segregating and testcross progenies derived by crossing ‘Indis’ to four bread wheat cultivars. The severity of the gametocidal response in the heterozygotes ranged from a virtually exclusive transfer of the translocation to an almost normal transmission of the homologues. In some genetic backgrounds an intermediate level of transmission occurred. In the F₁ with a gametocidal response, the transmission of the normal chromosome 7D was reduced in both sexes, but the reduction may be more severe in the male germline.     

Intergeneric Transfer (Rye to Wheat) of a Gene(s) for Russian Wheat Aphid Resistance

An octoploid triticale was derived from the F, of a Russian wheat aphid-resistant rye, ‘Turkey 77’, and ‘Chinese Spring’ wheat. The alloploid was crossed to common wheat, and to ‘Imperial’ rye/‘Chinese Spring’ disomic addition lines. F₂, progeny from these crosses were tested for Russian wheat aphid resistance and C-banded. A resistance gene(s) was found to be associated with chromosome arm IRS of the ‘Turkey 77’ rye genome. A monotelosomic IRS (‘Turkey 77’) addition plant was then crossed with the wheat cultivar ‘Gamtoos’, which has the 1BL.1RS ‘Veery’ translocation. Unlike the IRS segment in ‘Gamtoos’, the ‘Turkey 77’-derived 1 RS telosome did not express the rust resistance genes Sr31 and Ar26, which could then be used as markers. From the F, a monotelosomic 1 RS addition plant that was also heterozygous for the 1BL. 1 RS translocation was selected and testerossed with an aphid-susceptible common wheat, ‘Inia 66’ Meiotic pairing between the rye arms resulted in the recovery of five euploid Russian-wheat-aphid-resistant plants. One recombinant also retained Sr31 and Lr26 and was selfed to produce translocation homozygotes.     

Isolation of a Spontaneous Chromosome Translocation in Common Wheat

The genes Ms2 for male sterility and Rht10 for dominant dwarfing located on the short arm of chromosome 4D in common wheat arc closely linked. Male sterile, dwarf F₁ plants from the cross of male sterile‘Chinese Spring’× dwarf‘Ai-bian’were backcrossed with the variety‘Chinese Spring, From this offspring a spontaneous chromosome translocation was isolated resulting in a recombinant male sterile and dwarf genotype.     

Stripe rust resistance gene Yr18 and its suppressor gene in Chinese wheat landraces

The slow‐rusting and mildewing gene Yr18/Lr34/Pm38/Sr57 confers partial, durable resistance to multiple fungal pathogens and has its origins in China. A number of diagnostic markers were developed for this gene based on the gene sequence, but these markers do not always predict the presence of the resistant phenotype as some wheat varieties with the gene are susceptible to stripe rust in China. We hypothesized that these varieties have a suppressor of Yr18. This study was undertaken to determine the presence of Yr18, the suppressor and/or another resistance gene in 144 Chinese wheat landraces using molecular markers and stripe rust field data. Forty‐three landraces were predicted to have Yr18 based on the presence of the markers, but had final disease severities higher than 70%, indicating that this gene may be under the influence of a suppressor. Four of these landraces, ‘Sichuanyonggang 2’, ‘Baikemai’, ‘Youmai’ and ‘Zhangsihuang’, were chosen for genetic studies. Crosses were made between the lines and ‘Avocet S’, with further crosses of Sichuanyonggang 2 ×  ‘Huixianhong’ and Sichuanyonggang 2 ×  ‘Chinese Spring’. The F₁ plants of Sichuanyonggang 2/Chinese Spring was susceptible indicating the presence of a dominant suppressor gene. The results of genetic analyses of F_2:3 and BC₁F₂ families derived from these crosses indicated the presence of Yr18, a Yr18 suppressor and another additive resistance gene. The Yr18 region in Sichuanyonggang 2 was sequenced to ensure that it contained the functional allele. This is the first report of a suppressor of Yr18/Lr34/Pm38/Sr57 gene with respect to stripe rust response.     

Cytological analyses of hybrids and derivatives of hybrids between durum wheat and Thinopyrum bessarabicum,using multicolour fluorescent GISH*

The wheat progenitors and other wild relatives continue to be important sources of genes for agronomically desirable traits, which can be transferred into durum wheat (Triticum turgidum; 2n = 4x = 28; AABB genomes) cultivars via hybridization. Chromosome pairing in durum × alien species hybrids provides an understanding of genomic relationships, which is useful in planning alien gene introgression strategies. Two durum cultivars, ‘Lloyd’ and ‘Langdon’, were crossed with diploid wheatgrass, Thinopyrum bessarabicum (2n = 2x = 14; JJ), to synthesize F₁ hybrids (2n = 3x = 21; ABJ) with Ph1. ‘Langdon’ disomic substitution 5D(5B) was used as a female parent to produce F₁ hybrids without Ph1, which resulted in elevation of pairing between durum and grass chromosomes – an important feature from the breeding standpoint. The F₁ hybrids were backcrossed to respective parental cultivars and BC₁ progenies were raised. ‘Langdon’ 5D(5B) substitution × Th. bessarabicum F₁ hybrids were crossed with normal ‘Langdon’ to obtain BC₁ progeny. Chromosome pairing relationships were studied in F₁ hybrids and BC₁ progenies using both conventional staining and fluorescent genomic in situ hybridization (fl‐GISH) techniques. Multicolour fl‐GISH was standardized for characterizing the nature and specificity of chromosome pairing: A–B, A–J and B–J pairing. The A–J and B–J pairing will facilitate gene introgression in durum wheat. Multicolour fl‐GISH will help in characterizing alien chromosome segments captured in the durum complement and in their location in the A and/or B genome, thereby accelerating chromosome engineering research.     

The linkage between the stem rust resistance gene Sr2 and pseudo-black chaff in wheat can be broken

Recessively inherited gene Sr2 has provided the basis of durable resistance to stem rust (caused by Puccinia graminis tritici) in wheat (Triticum aestivum L.) worldwide. The associated earhead and stem melanism or ‘pseudo‐black chaff’ is generally used as a marker for this gene. Sr2 has been postulated in many wheat cultivars of India including ‘Lok 1’, based on associated pseudo‐black chaff in adult plants, and leaf chlorosis in seedlings. However, dominant inheritance of the resistance factor operating in ‘Lok 1’, and a 13 : 3 (resistant : susceptible) F₂ segregation in the ‘Sr2‐line’ (‘Chinese Spring’⁶ × ‘Hope’ 3B) × ‘Lok 1’ cross confirmed that Sr2 was absent in ‘Lok 1’. Susceptible plants with a pseudo‐black chaff phenotype were observed in F₂ populations of ‘Agra Local’ (susceptible) × ‘Lok 1’, and the ‘Sr2‐line’ × ‘Lok 1’ crosses. Most of the F₃ families derived from the susceptible F₂ segregants with pseudo‐black chaff phenotypes were true breeding for the expression of pseudo‐black chaff with susceptibility to stem rust. Thus, linkage of pseudo‐black chaff with Sr2 in wheat can be broken, and hence, caution may be exercised in using pseudo‐black chaff as a marker for selecting Sr2 in breeding programmes.     

Effects of Wheat Chromosome 1D Telosomes on Hybrid Seed Development in Wheat × Rye Crosses

Pollination of ‘Chinese Spring,’ monosome 1D plants with rye results in failure of hybrid seed development in a proportion of the F₁ seeds corresponding to the transmission rate of the nullisomic 1D egg cells. Development and viability of these hybrid seeds closely resemble that normally observed in T. aurum× rye crosses. Using ‘Chinese Spring’ chromosome ID telosomic plants in crosses with rye, it was possible to illustrate that the observed effect was associated with the long arm of this chromosome.     

Segregation distortion in common wheat of a segment of Thinopyrum intermedium chromosome 7E carrying Bdv3 and development of a Bdv3 marker

Yellow dwarf (YD) disease is one of the most destructive diseases of cereals worldwide. Wheat (Triticum aestivum L.)–Thinopyrum intermedium 7E(7D) substitution line P29 carries resistance to YD, known as Bdv3, that originates on the long arm of chromosome 7E of Th. intermedium, and the resistance was introgressed into wheat chromosome 7D as T7DS.7DL–7EL in the translocation lines P961341 and P98134. Until now, quantification of YD viruses in cereal crops was usually done by enzyme‐linked immunosorbent assay (ELISA), which is time consuming and laborious. To facilitate this analysis, SSR‐Bdv3, a diagnostic molecular marker, was developed in this study. The transmission of the Th. intermedium segment with Bdv3 was investigated using the SSR‐Bdv3 marker and ELISA in F₂ and testcross progeny derived by crossing two wheat–Th. intermedium translocation lines to four common wheat cultivars. A Th. intermedium chromosome 7E segment in the translocation line P98134 was preferentially transmitted through male gametes in all of its crosses with the four wheat cultivars. However, the transmission frequency of the Th. intermedium 7E segment in another wheat–Th. intermedium translocation line, P961341, varied in different genetic backgrounds. The F₂ populations from reciprocal crosses of Chinese Spring and P961341 showed good fits to the expected ratio of 1 : 2 : 1. In this study, male preferential transmission for either chromosome 7E or chromosome 7D was observed in the progeny derived by crossing P961341 to other wheat cultivars.     

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.     

Monosomic analysis of Helminthosporium leaf blight resistance genes in wheat

A set of 21 monosomic (2n ‐ 1) and the disomic (2n) lines of the ‘Chinese Spring’ cultivar were crossed with ‘Chirya‐3′, the CIMMYT synthetic wheat line which has been identified as highly resistant for Helminthosporium leaf blight disease (HLB), in order to locate the genes governing disease resistance. The F₁ and segregating populations were challenged and screened against the most virulent pure mono‐conidial HLB isolate KL‐8 (Karnal, India). The F₁ progenies of the crosses were found to be susceptible because of the recessive nature of resistance. The F₂ progeny of the control cross (‘Chinese Spring’בChirya‐3’), segregated in the ratio of 1: 15 (resistant: susceptible), indicating that resistance to HLB was controlled by a pair of recessive genes. While the F₂ progeny of 19 monosomic crosses segregated in the ratio of 1: 15 (resistant: susceptible), the progeny of the remaining two crosses, 7B and 7D, deviated significantly from the ratio, revealing that 7B and 7D were the critical chromosomes for resistance genes that were located one on each chromosome. Moreover, the critical lines, 7B and 7D, confirmed the digenic complementary recessive nature of gene action by fitting well with the overall pooled F₂ segregation ratio of 13: 51 (resistant: susceptible) as expected for digenic complementary recessive resistance. The F₃ segregation ratios of the critical crosses, based on their pooled F₂ analysis, was estimated as 19: 32: 13 (non‐segregating susceptible: segregating as susceptible and resistant: non‐segregating resistant). F₃ progenies when tested with these ratios showed goodness‐of‐fit, confirming that the two pairs of recessive resistance genes were located on chromosomes 7B and 7D.     

Genomic constitution of a partial amphiploid OK7211542 used as a source of immunity to barley yellow dwarf virus for bread wheat

A combination of genomic in situ hybridization (GISH) and meiotic pairing analysis of crosses between a series of 2n= 56 partial amphiploids confirmed that the alien genome of the BYDV-immune Agro-tricum line OK7211542 is derived from Thinopyrum ponticum and not from Thinopyrum intermedium. The evidence from meiotic pairing analysis indicated that the chromosome constitution of OK7211542 is similar to another Agrotricum line, ORRPX, which was derived from a cross of wheat and Th. ponticum, but different from other Agrotricum lines, Zhong 5 and TAF 46 which were derived from the crosses between wheat and Th. intermedium. The GISH analysis confirmed that OK7211542 contained one complete set of 14 Th. ponticum chromosomes, in which no S chromosome was present in the alien genome. GISH also detected a small alien translocation attached to one of the wheat chromosomes, a result that was consistent with the pairing data.     

A Robertsonian translocation from Thinopyrum bessarabicum into bread wheat confers high iron and zinc contents

Development of wheat–alien translocation lines has facilitated practical utilization of alien species in wheat improvement. The production of a compensating Triticum aestivum–Thinopyrum bessarabicum whole‐arm Robertsonian translocation (RobT) involving chromosomes 6D of wheat and 6E^b of Th. bessarabicum (2n = 2x = 14, E^bE^b) through the mechanism of centric breakage–fusion is reported here. An F₂ population was derived from plants double‐monosomic for chromosome 6D and 6E^b from crosses between a DS6E^b(6D) substitution line and bread wheat cultivar ‘Roushan’ (2n = 6x = 42, AABBDD) as female parent. Eighty F₂ genotypes (L1–L80) were screened for chromosome composition. Three PCR‐based Landmark Unique Gene (PLUG) markers specific to chromosomes 6D and 6E^b were used for screening the F₂ plants. One plant with a T6E^bS.6DL centric fusion (RobT) was identified. A homozygous translocation line with full fertility was recovered among F₃ families and verified with genomic in situ hybridization (GISH). Grain micronutrient analysis showed that the DS6E^b(6D) substitution line and T6E^bS.6DL stock have higher Fe and Zn contents than the recipient wheat cultivar ‘Roushan’.     

Genetic basis of seedling-resistance to leaf rust in bread wheat 'Thatcher'

The bread wheat cultivar ‘Thatcher’ is documented to carry the gene Lr22b for adult‐plant resistance to leaf rust. Seedling‐resistance to leaf rust caused by Puccinia triticina in the bread wheat cultivar ‘Thatcher’, the background parent of the near‐isogenic lines for leaf rust resistance genes in wheat, is rare and no published information could be found on its genetic basis. The F₂ and F₃ analysis of the cross ‘Agra Local’ (susceptible) × ‘Thatcher’ showed that an apparently incompletely dominant gene conditioned seedling‐resistance in ‘Thatcher’ to the three ‘Thatcher’‐avirulent Indian leaf rust pathotypes – 0R8, 0R8‐1 and 0R9. Test of allelism revealed that this gene (temporarily designated LrKr1) was derived from ‘Kanred’, one of the parents of ‘Thatcher’. Absence of any susceptible F₂ segregants in a ‘Thatcher’ × ‘Marquis’ cross confirmed that an additional gene (temporarily designated LrMq1) derived from ‘Marquis’, another parent of ‘Thatcher’, was effective against pathotype 0R9 alone. These two genes as well as a second gene in ‘Kanred’ (temporarily designated LrKr2), which was effective against all the three pathotypes, but has not been inherited by ‘Thatcher’, seem to be novel, undocumented leaf rust resistance genes.     

Chromosome location of genes affecting polyphenol oxidase activity in seeds of common and durum wheat

This study used cytogenetic stocks to investigate the chromosomal location of genes responsible for polyphenol oxidase (PPO) activity in common and durum wheat seeds. Substitution lines of chromosome 2A of hexaploid varieties ‘Cheyenne’, ‘Thatcher’ and ‘Timstein’ in ‘Chinese Spring’ showed significantly higher PPO activity than all other substitution lines of the same variety, with the exception of substitutions of ‘Cheyenne’ chromosome 3A and ‘Thatcher’ chromosome 4B. Substitution lines of chromosome 2A of Triticum turgidum var. dicoccoides and of chromosome 2D of ‘Chinese Spring’ into the tetraploid variety ‘Langdon’ showed a significant increase in PPO activity relative to all other substitution lines in Langdon. The gene(s) responsible for high PPO activity in chromosome 2D from ‘Chinese Spring’ was mapped on the long arm within a deletion that represents 24% of the distal part of the arm. This study shows that genes located in homoeologous group 2 play a major role in the activity of PPO in wheat.     

Recessive genes controlling resistance to Helminthosporium leaf blight in synthetic hexaploid wheat

A study was conducted under controlled environment conditions in a phytotron to determine the nature of the inheritance of resistance Helminthosporium leaf blight (HLB) in a synthetic hexaploid wheat line, ‘Chirya‐3’, against the isolate KL‐8 of Bipolaris sorokiniana from the major wheat growing region of India. Crosses were made between two susceptible lines ‘WH 147’ and ‘Chinese Spring’. Analyses of F₁ and F₂ populations of these two crosses (‘WH 147’בChirya‐3’ and ‘Chinese Spring’בChirya‐3’) showed that resistance against the isolate in ‘Chirya‐3’ was governed by two recessive genes functioning in a complementary interaction giving an F₂ segregation pattern of 1 : 15 (resistant : susceptible). The segregation pattern of the resistant F₂ progenies in F₃ families from both crosses confirmed that two homozygous recessive genes were responsible for resistance to the isolate of Bipolaris sorokiniana in the synthetic line ‘Chirya‐3’. It is proposed that the genes be designated as hlbr1 and hlbr2.     

Genetics of adult plant stripe rust resistance in four Australian wheats and the French cultivar 'Hybride-de-Bersée'

Long-term resistance to rust diseases depends on the identification and use of durable resistance sources or on the continuing use of new resistances and combinations of genes for specific resistance. These studies include four Australian wheats with intermediate, but inadequate levels of resistance and a French wheat ‘Hybride-de-Bersée’ (‘Bersee’), with reputed durable resistance to stripe rust. Studies of F₂ and F₃ populations from crosses with the susceptible ‘Avocet’ indicated that intermediate levels of adult plant stripe rust resistance in cultivars ‘Harrier’, ‘Flinders’ and ‘M2435’ were inherited monogenically, whereas King possessed two genes for resistance. Cultivars Harrier and M2435 possessed the same gene. Similarly, cvs. King and Flinders carried a gene in common. Like ‘Harrier’ and ‘M2435’, ‘King’ and ‘Flinders’ share common parents. The higher level of resistance in ‘Bersee’ was controlled by four genes. This conclusion was based on conventional genetic analysis, tests on F₂-derived F₇ single-seed descent lines and testcross progenies.     

A New Source of Resistance to Pseudocercosporella herpotrichoides, Cause of Eyespot Disease of Wheat, Located on Chromosome 4V of Dasypyrum villosum

Resistance to Pseudocercosporella herpotrichoides in five wheat cultivars, accession W6 7283 of Dasypyrum villosum, and ‘Chinese Spring’ disomic addition lines of the D. villosum chromosomes IV, 2V, 4V, 5V, 6V and 7V, was evaluated in seedlings by measuring disease progress 6 weeks after inoculation with a β—glucuronidase—transformed strain of the pathogen and by visual estimates of disease severity. D. villosum and the disomic addition line of chromosome 4V were as resistant as wheat cultivars ‘VPM—1’ and ‘Cappelle Desprez’, but less resistant than ‘Rendezvous’. Resistance of the chromosome 4V disomic addition line was equivalent to that of D. villosum.‘Chinese Spring’ and disomic addition lines of IV, 2V, 5V, 6V and 7V were all susceptible. These results confirm Sparaguee's (1936) report of resistance in D. villosum to P. herpotrichoides and establish the chromosomal location for the genes controlling resistance. The presence of chromosome 4V in the addition line and its homocology to chromosome 4 in wheat were confirmed by Southern analysis of genomic DNA using chromosome group 4-specific clones. This genetic locus is not homoeologous with other known genes for resistance to P. herpotrichoides located on chromosome group 7, and thus represents a new source of resistance to this pathogen.     

A leaf rust resistance gene, different from Lr34, associated with leaf tip necrosis in wheat

The gene Lr34 has contributed to durable resistance to leaf rust caused by Puccinia triticina in wheat worldwide. The closely associated leaf tip necrosis is generally used as the gene's marker. Lr34 has been postulated in many Indian bread wheat cultivars including ‘C 306’, based on the associated leaf tip necrosis and a few other field and glasshouse observations. The present study showed monogenic control of adult‐plant resistance in ‘C 306’ to leaf rust pathotype 77‐5 (121R63‐1). The F₂ segregation in the crosses between ‘C 306’ and the two known carriers of Lr34, ‘Line 897’ and ‘Jupateco 73’‘R’ fitted a digenic ratio. The F₃ families derived from the susceptible F₂ segregants were true breeding for susceptibility, proving the absence of Lr34 in ‘C 306’. The cross between ‘Line 897’ and ‘Jupateco 73’‘R’ did not segregate for susceptibility. Resistance in the cross ‘Agra Local’ (susceptible) × ‘C 306’ was associated with leaf tip necrosis, showing that the leaf rust resistance gene in ‘C 306’ was associated with leaf tip necrosis, but was different from Lr34. This gene is being temporarily designated as Lr‘C 306’. Hence, leaf tip necrosis cannot be considered as an exclusive marker for selecting Lr34 in wheat improvement.     

Chromosome locations of leaf rust resistance genes in selected tetraploid wheats through substitution lines

Langdon durum D-genome disomic substitution lines were used to study the chromosome locations of adult-plant leaf rust resistance genes identified from tetraploid wheat accessions. The accessions are 104 (Triticum turgidum subsp. dicoccum var. arras) and 127 (T. turgidum subsp. durum var. aestivum). The complete sets of the substitution lines were crossed as female parents with the accessions and F₁ double monosomic individuals selected at metaphase I. Segregating F₂ individuals were inoculated during the flag leaf stage with pathotype UVPrt2 of Puccinia triticina. The substitution analysis involving accession 104 showed that the gene for leaf rust resistance is located on chromosome 6B. The analysis with accession 127 indicated that chromosome 4A carries a gene for leaf rust resistance. The two novel genes are temporarily designated as Lrac104 and Lrac127, respectively from accessions 104 and 127.     

Association of leaf rust and powdery mildew resistance in a recombinant derived from a Hordeum vulgare × Hordeum bulbosum hybrid

While studying powdery mildew resistance in a recombinant line (code 81882) derived from a Hordeum vulgare (cv. ‘Vada’) ×Hordeum bulbosum hybrid, a low infection type of resistance to leaf rust was observed. To determine the mode of inheritance of the leaf rust resistance and whether there was linkage between the two resistances, F₂ and F₃ progenies from crosses between 81882 and ‘Vada’ were inoculated with the leaf rust and powdery mildew pathogens. Southern blots were prepared using restricted DNA extracted from leaves of 82 F₂ plants and four chromosome 2HS sequences were hybridized with the blots to define the length of the introgression. The leaf rust resistance appears to be inherited as a single dominant gene on chromosome 2HS, which co-segregates with the powdery mildew resistance. There was an almost complete association between the resistances and the respective molecular markers, but it is likely that the strong linkage results from the frequent inheritance of the introgressed H. bulbosum DNA as an intact segment of chromatin with only low levels of recombination within the segment.