Identification and molecular tagging of a stripe rust resistance gene in wheat line P81

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most devastating diseases in common wheat ( Triticum aestivum L.). With the objective of identifying and tagging a new gene for resistance to stripe rust in wheat line P81, F₁, F₂ and F_2:3 populations from the cross 'Chuanmai 28'/P81 were inoculated with Chinese PST race CYR32 in greenhouse and field trials. P81 carried a single dominant gene for resistance (designated YrP81 ) to CYR32. Tests of allelism showed that YrP81 was different from Yr5 , Yr10 , Yr15 and Yr26 . Simple sequence repeat (SSR) and resistance gene-analogue polymorphism (RGAP) between the parents were used for genotyping the F₂ populations. YrP81 was closely linked to four SSR loci on chromosome 2BS with genetic distances of 18.3 cM ( Xwmc25 ), 1.8 cM ( Xgwm429 ), 4.1 cM ( Xwmc770 ) and 5.3 cM ( Xgwm148 ). Two RGAP markers RGA1 (NLRR/XLRR) and RGA2 (Pto kin4/NLRR-INV2) were also closely linked to YrP81 with genetic distances of 4.7 and 6.3 cM, respectively. The linkage map of YrP81 and molecular markers was established in the order Xwmc25 - RGA2 - RGA1 - Xgwm429 - YrP81 - Xwmc770 - Xgwm148 . Pedigree analysis, response patterns with Chinese PST races and associations with markers suggested that YrP81 is a novel stripe rust resistance gene. The PCR-based microsatellite and RGAP markers identified here could be applied in selection of YrP81 in wheat breeding.     

Inheritance and gene tagging of male fertility restoration of cytoplasmic-nuclear male-sterile line NJCMS1A in soybean

The F₁, F₂ and F_2:3 of the NJCMS1A × 'Zhongdou 5' cross were used to analyse the inheritance of the male fertility restoration of the cytoplasmic-nuclear male-sterile line NJCMS1A in soybean. The results of genetic analysis showed two pairs of dominant genes conferring the male fertility restoration of NJCMS1A, which further confirmed previous results. The F₂ population from the NJCMS1A × 'Zhongdou 5' cross was used for tagging the restorer genes for NJCMS1A with 664 pairs of simple sequence repeat primers selected randomly from the genetic linkage map of soybean published by Cregan et al. (1999) . Satt626 on linkage group M and Satt300 on linkage group A1 of the integrated linkage map by Song et al. (2004) were found to link to the two restorer genes of NJCMS1A. The maximum-likelihood estimates of the genetic distance between the two markers, Satt626 and Satt300, and the two restorer genes of 'Zhongdou 5' were 9.75 and 11.18 cM, respectively.     

Development of co-dominant amplified polymorphic sequence markers for resistance of sunflower to downy mildew race 730

The inheritance of the reaction of sunflower to downy mildew was investigated using resistant and susceptible near isogenic lines (NILs) and their F₃ families. Resistance to race 730 was evaluated using the whole seedling inoculation technique. Seventy-three F₃ families were inoculated, among which 54 families were resistant and 19 susceptible, fitting a 3 : 1 segregation ratio. F₃ families were also studied using several PCR markers. Ten markers at the Pl6 locus, specific for the resistant line, also segregated in F₃ families with a 3 : 1 ratio. The same segregation ratio occurred for microsatellite haplotypes that resembled the resistant parent, and were amplified with ORS 166 and ORS 1043. The only common fragment that was observed between resistant and susceptible parental lines was one of the TIR-NBS-LRR resistance gene analogue markers, having a restriction site. Two co-dominant cleaved amplified polymorphic sequence (CAPS) markers were obtained. The mapping data indicate that several dominant markers and two CAPS markers, developed here, completely co-segregate with the Pl6 gene conferring resistance to race 730. CAPS markers will facilitate efficient marker-assisted selection for sunflower resistance to downy mildew race 730.     

Cytogenetic analysis of F1, F2 and BC1 plants from intergeneric sexual hybridization between Sinapis alba and Brassica oleracea by genomic in situ hybridization

By intergeneric sexual hybridization between Sinapis alba and Brassica oleracea , F₁, F₂ and BC₁ progeny plants were produced. S. alba plants (genome SS, 2n = 24) were pollinated with B. oleracea (genome CC, 2n = 18), and the fertile F₁ plants were pollinated with B. oleracea to obtain BC₁ plants. GISH analysis showed that 10 out of 12 F₁ plants had 12 S. alba chromosomes (one full S chromosome set) and nine B. oleracea chromosomes (one C chromosome sets), representing the expected hybrids. However, two F₁ plants had 12 S chromosomes and 18 C chromosomes (two C chromosome sets), indicating unexpected hybrids. A maximum of three trivalents between C and S chromosomes were identified at metaphase I of semi-fertile F₁ pollen mother cells (PMCs), which indicates homology and chromosome pairing between these two genomes. The C genome had obviously been doubled in two F₂ plants from selfed semi-fertile F₁ plants. BC₁ plants consisted of 18 C chromosomes and different numbers of one, five and six additional S chromosomes, respectively. Monosomic alien addition lines developed in the present study can be used for B. oleracea breeding and Sinapis alba gene mapping.     

Identification of AFLP and RAPD markers linked to anthracnose resistance in grapes and their conversion to SCAR markers

Resistance to anthracnose or black spot ( Elsinoe ampelina ), a serious fungal pathogen in viticulture and table grape production, was investigated on 25 grape cultivars. Bioassays performed with culture filtrates produced by the pathogen revealed 14 resistant genotypes. In most plants resistance originated from Vitis labrucsa but also genotypes with V. rupestris and V. riparia  ×  V. rupestris background showed resistance. Genetic analysis was conducted in F₁, S₁ and BC₁ plants developed from various cultivars. In total, 326 F₁ plants were evaluated, 172 genotypes proofed to be resistant, whereas 154 were susceptible to anthracnose. A Mendelian segregation ratio of 1 : 1 (χ² = 0.30–0.65) indicating that anthracnose resistance is controlled by a single dominant gene. To facilitate the use of marker-assisted selection in grape-breeding PCR-based markers were developed by random amplified polymorphic DNA and amplified fragment length polymorphism in bulk segregant analysis. Finally, OPB 15₁₂₄₇ was developed as a sequence characterized amplified region marker being diagnostic for the locus of resistance to anthracnose in all resistant genotypes tested. Within the 25 grape cultivars OPB 15₁₂₄₇ is diagnostic in the genetic background of both V. labrucsa and V. rupestris and V. riparia  ×  V. rupestris .     

Development of STS markers and QTL validation for common bacterial blight resistance in common bean

Common bacterial blight (CBB) of common bean ( Phaseolus vulgaris L.), is one of the major diseases that decrease yield and quality. A major quantitative trait locus (QTL) for CBB resistance from line XAN 159 was transferred into two bean lines, HR45 and HR67. Previous studies identified that two markers are linked to this QTL but the chromosome location was not consistent. To identify more tightly linked markers and to verify the chromosome location, 65 additional markers were mapped using 81 recombinant inbred lines (RILs) derived from a cross HR67 × OAC95-4. The QTL was mapped to a 13 cM region on chromosome 1 and defined by eight molecular markers that explained 25–52% of the phenotypic variation. Six tightly linked amplified fragment length polymorphism markers (0.6–9.7 cM from the QTL peak) were converted into seven sequence tagged site markers, three of which were mapped to this QTL. Five tightly linked markers were used to screen 907 F₂ plants derived from a cross HR45 × 'OAC Rex' and four of them were linked to each other within 4.2 cM. These markers may be useful in marker-assisted selection and map-based cloning of this major QTL.     

Pea weevil, Bruchus pisorum L. (Coleoptera: Bruchidae), resistance in Pisum sativum×Pisum fulvum interspecific crosses

The pea weevil, Bruchus pisorum (L.), is one of the most intractable pest problems of cultivated pea, Pisum sativum L., in the world. This study investigated the transfer of pea weevil resistance from two accessions (PI 595946, PI 343955) of wild pea, Pisum fulvum Sibth. & Sm., to interspecific populations derived from crossing these accessions with a weevil-susceptible pea cultivar ('Alaska 81'). Partial life tables characterized weevil stage-specific mortality and survivorship on parents and interspecific progeny in two glasshouse trials. Larval mortality rates on pods (F₃ plants) of several F_2:3 families were between 36.0% and 52.9%. These means were statistically similar to mean mortality rates on pods of resistant parents (45.4% and 46.2%), but significantly greater than mean rates on the susceptible parent (1.2% and 10.6%). Pod surface characteristics contributed to high neonate larval mortality on pods of resistant parents and interspecific progeny. Seed resistance was not broadly transferred to interspecific progeny [revealed by high weevil survivorship in seeds (means mostly >80%) and high seed damage ratings of 3–5 where ratings of 1–2 denote resistance (production of resistant seed averaged 4.2% to 22.8%)]. Estimates of total weevil mortality on pods and seeds of eight F_2:3 families were 50–70%. Thus, weevil resistance in the Pisum secondary gene pool can be transferred to interspecific progeny, thereby providing a potential avenue to develop weevil-resistant pea cultivars.     

Co-localization of quantitative trait loci for foliar disease resistance in sorghum

Quantitative trait loci (QTL) analysis of resistance to three foliar diseases, viz. target leaf spot, zonate leaf spot and drechstera leaf blight was undertaken in sorghum using 168 F₇ recombinant inbred lines derived from a cross between '296B' (resistant) and 'IS18551' (susceptible) parents. The genomic region flanked by plant colour locus ( Plcor ) and simple sequence repeat marker Xtxp95 on chromosome SBI-06 harboured disease-response QTL for all the three diseases caused by different fungal pathogens. It is hypothesized that this region on sorghum chromosome SBI-06 could harbour a cluster of disease-response loci to different pathogens as observed in the syntenic regions on rice chromosome 4 and maize chromosome 2. The information gained in this study can be used in deploying marker-assisted selection for foliar resistance and map-based isolation of important disease resistance genes in sorghum.     

Molecular mapping of a new red mutant gene (Rs) in upland cotton

In recent years, there has been slow progress in improving cotton yield. It is known that the F₁ generation from the cross of the new red mutant and the normal green leaf plant has high photosynthetic efficiency. Therefore, cloning the new red mutant gene and further introducing it into other crops through transgenic techniques is a promising approach for achieving high photosynthetic efficiency through breeding. To map this new mutant gene, tentatively named R _s , the authors constructed an F₂ generation containing 1214 individual plants from mutant EH083 ( Gossypium hirsutum ) and Hai 7124 ( Gossypium barbadense ). Fifty-five pairs of simple sequence repeats and sequence-related amplified polymorphism (SRAP) primers on chromosome 7 were selected to screen the two parents. Finally, the R _s gene was mapped at the 0.3 cM interval flanked by markers NAU3735 and NAU1048.     

A CAPS marker TAO1902 diagnostic for the I-2 gene conferring resistance to Fusarium oxysporum f. sp. lycopersici race 2 in tomato

Fusarium oxysporum f. sp. lycopersici inhabits most tomato-growing regions worldwide, causing tomato production yield losses. A molecular marker linked to resistance would be useful for tomato improvement programmes. Thus, a cleaved amplified polymorphic sequence (CAPS) marker TAO1₉₀₂ was developed to identify tomato genotypes possessing the I-2 gene, which confers resistance to F. o. lycopersici race 2. The Rsa I or Fok I restriction fragments corresponded to the presence or absence of the I-2 allele in a segregating 100 F₂ progeny, tomato cultivars, 16 resistant and 20 susceptible to Fusarium wilt, respectively, lines and F₁ hybrids, representing various tomato gene pools. TAO1₉₀₂ may be helpful for selection of F. o. lycopersici -resistant tomato germplasm.     

Uniparental inheritance of purple leaf and the associated resistance to leafminer in castor bean

Leafminer ( Liriomyza trifolii Burgess), Diptera Agromyzidae, is one of the insect pests that causes economic damage to castor bean ( Ricinus communis L.) foliage. Green leaf type is a common phenotype in castor bean and highly susceptible to leafminer. The rare purple leaf type germplasm accessions showed stable resistance to leafminer. Studies were carried out to understand the inheritance of purple leaf and the associated leafminer resistance. Direct and reciprocal crosses were made between a purple leaf parent RG1930 and a green leaf parent RG2788. RG1930 is resistant to leafminer while RG2788 is susceptible. Reciprocal differences were noted in segregation pattern of purple leaf colour as well as resistance to leafminer. Purple leaf phenotype was obtained only in purple × green (RG1930 × RG2788) cross where the female parent was a purple leaf phenotype. The reciprocal cross green × purple (RG2788 × RG1930) produced only the green leaf phenotype. Uniparental inheritance was observed for purple leaf phenotype and resistance to leafminer in F₁, F₂, F₃ and backcross generations. Progenies with a dark purple leaf were resistant to leafminer while those with a green leaf were susceptible. Visual association between a purple leaf and resistance to leafminer and their uniparental inheritance were clearly established. The role of heritable epigenetic effects are discussed in expression of purple pigment in offspring.     

Relationships between seed oil content and fatty acid composition in high stearic acid sunflower

The high stearic acid sunflower mutant CAS-3 is characterized by a low seed oil content, which might represent a constraint for the commercial production of high stearic acid sunflower oil. The objective of the present research was to investigate the relationships between fatty acid profile and seed oil content in CAS-3. Plants of CAS-3 were reciprocally crossed with plants of breeding line ADV-37, with high oil content and standard fatty acid profile. Oil content and fatty acid composition were measured in individual F₂ seeds and F₂ plants (F₃ seeds averaged). Both F₂ seeds and F₂ plants from the cross ADV-37 × CAS-3 had a significantly higher oil content than those from the reciprocal cross, which indicated the existence of cytoplasmic effects in the genetic control of the trait. A consistent negative correlation between oil content and palmitic acid and a positive correlation between oil content and oleic acid were detected both in F₂ seeds and F₂ plants. Conversely, no consistent correlation between oil content and stearic acid was observed, which suggested the feasibility of simultaneous selection for both traits.     

Hybridization of Thinopyrum distichum and Secale cereale

An attempt was made to determine whether the salt tolerance genes of Thinopyrum distichum would be expressed in the presence of the rye genomes and if it would be possible to improve and utilize its hybrid with rye as a salt-tolerant fodder crop. Th. distichum florets were pollinated with diploid and tetraploid rye but hybrids were obtained only with tetraploid rye. The F₁ had 28 chromosomes and expressed high levels of salt tolerance. Fertility could not be induced through colchicines treatment but the plants produced some apomictic seeds during the summer months. The F₂ had 20-22 chromosomes and retained two complete or near-complete rye genomes. The F₂ plants responded better to colchicine treatment, however, the doubled hybrids remained male sterile. In summer, one F2 plant produced many apomictic seeds with chromosome numbers ranging from 14 to 16 (primarily rye chromosomes). The mechanism that caused the preferential loss of Thinopyrum chromosomes in each apomictic cycle remains unknown. The F₃ phenotypically resembled rye, had primarily reductional male meioses and produced seemingly functional pollen, but were self-sterile.     

Molecular mapping of genic male-sterile genes ms15, ms5 and ms6 in tetraploid cotton

Two genic male sterile (GMS) lines, Lang-A conditioned by ms ₁₅ and Zhongkang-A conditioned by ms ₅ ms ₆ duplicate recessive genes in Gossypium hirsutum L., were chosen to map GMS genes. These two lines were crossed with Gossypium barbadense cv. 'Hai7124' to produce segregating populations. The ms ₁₅ gene was mapped on chromosome 12, and was flanked by two simple sequence repeat (SSR) markers, NAU2176 and NAU1278, with a genetic distance of 0.8 and 1.9 cM respectively. The ms ₅ and ms ₆ genes were mapped to one pair of homoeologous chromosomes, ms ₅ on chromosome 12 flanked by three SSR markers, NAU3561, NAU2176 and NAU2096, with genetic distances of 1.4, 1.8 and 1.8 cM, respectively, and ms ₆ on chromosome 26 flanked by two SSR markers, BNL1227 and NAU460, with a genetic distance of 1.4 and 1.7 cM respectively. These tightly linked markers with the ms ₁₅ , ms ₅ and ms ₆ genes can be used in the marker-assisted selection among segregating populations in a breeding programme, and provide the foundation for gene isolation by map-based cloning for these three genes.     

A high-resolution map of the rice blast resistance gene Pi15 constructed by sequence-ready markers

The gene Pi15 for resistance of rice to Magnaporthe grisea was previously mapped to a ≈0.7-cM region on chromosome 9. To further define the chromosomal region of the Pi15 locus, a contig spanning the locus was constructed, in silico , through bioinformatics analysis using a reference sequence of the cultivar 'Nipponbare'. One simple sequence repeat marker adopted from the International Rice Microsatellite Initiative and six candidate resistance gene (CRG) markers, developed from gene annotation of the reference sequence of the contig, were used for linkage analysis in a mapping population consisting of 504 extremely susceptible F₂ plants. The Pi15 locus was delimited to a ≈0.5-cM region flanked by the markers CRG5 and CRG2 and co-segregated with the markers BAPi15₇₈₂, CRG3 and CRG4, which was physically converted to a 44-kb interval.     

Production of intergeneric hybrids between Raphanm and Moricandia

Intergeneric F₁ hybrids between Raphanus sativus (2n = 18, RR) and Moricandia arvensis (2n = 28, MaMa) have been produced through ovary culture followed by embryo culture, when M. arvensis was used as a pistillate parent. Six BC₁ plants were also obtained through ovary culture followed by embryo culture in the backcross of an amphidiploid F₁, hybrid with R. sativus cv. 'Pink ball'. Two BC₁ plants were ses-quidiploids (2n = 32, MaRR), and the other BC₁, plants were hyperploid with 2n = 55, having MaMaRRR genomes. BC₂, seeds were obtained by conventional pollination in the successive backcross of two sesquidiploid BC₁, plants with R. sativus cv. 'Pink ball'. Their seed set percentages were 12.7% and 17.0%, respectively. These novel hybrid plants and derived progenies may be valuable materials for the genetic investigation and breeding of Brassiceae , including R. sativus.     

Relationship of Root and Shoot Characters in Parent, F1 and F2 Populations of Rice

The direct and indirect contributions of root characters — root length, roots/plant, fresh and dry root weight on grain yield/plant were worked out from a 7 × 7 diallel set of rice hybrids. The materials were grown in pots with four replications. Path analysis was done at genotypic level of correlation.
The grain yield/plant showed positive correlation with all the root characters in parent, F₁ and F₂ except with roots/plant in F₁ population. Fresh root weight demonstrated positive direct effect on grain yield/plant in all the three generations. Roots/plant had highly positive direct effect in F₂. Direct effects were negative in respect of root length and dry root weight in F₂ generation.     

Identification and inheritance of a new gene for powdery mildew resistance in mungbean (Vigna radiata L. Wilczek)

Powdery mildew (PM) is one of the important foliar diseases of mungbean. Resistance sources have been identified in India and the inheritance studies showed that complete resistance (RO) was controlled by two dominant genes, Pm1 , Pm2 . The breakdown of complete resistance (RO) into moderate resistance (R2) by race-2 (Akola) has been reported. It is assumed that the change in resistance reaction is due to a mutation in the pathogen. The present investigation was carried out with a view to screen germplasm, cultivars and mutants for identification of complete resistance (RO) sources against race-2 and to study their inheritance. 'Mulmarada', a local mungbean cultivar from Maharashtra state of India was identified as a complete resistance (RO) source for race-2. The inheritance of Mulmarada's resistance (RO) was studied. The F₁ and the segregation in F₂ and F₃ showed that the complete resistance (RO) in 'Mulmarada' is controlled by a single dominant gene, which is different from the earlier identified Pm1 and Pm2 resistance genes. Mulmarada's resistance gene is designated as Pm3 for PM resistance.     

Identification of a SCAR marker linked to a recessive male sterile gene (Tems) and its application in breeding of marigold (Tagetes erecta)

In marigold, an F₂ segregation population of 167 plants was constructed from a cross of a line (M525A) carrying the male sterility trait × an inbred line (f53f). In line M525A, the male sterility trait was controlled by the recessive gene, Tems . The intersimple sequence repeat (ISSR) and sequence-related amplified polymorphism (SRAP) techniques combined with bulked segregant analysis were used to develop markers linked to the trait. From a survey of the 38 ISSR primers and 170 SRAP primer combinations, only one SRAP marker that was closely linked to the target trait was identified and successfully converted into sequence characterized amplified region (SCAR) marker that was located within 2.4 cM from Tems locus. The marker was validated with five other two-type lines and in each case the male fertile plants were reliably identified. This SCAR marker therefore permits the efficient marker-assisted selection of male sterile individuals in breeding programmes of marigold and will greatly facilitate the breeding of F₁ cultivars.     

Evaluation of the Heterosis on Leaf Photosynthesis of Remote-Cross F1 Rice (Oryza saliva L.)

The heterosis of leaf photosynthesis was studied on the main characters included in the range from CO₂exchange rate (CER) to enzymatic activity using a remote cross F, rice. The CER was significantly higher than those of the parental strains, showing a 111 % heterosis effect on average; at the same time strong heterosis was observed for the leaf area production and growth. Also stomatal and mesophyll conductances increased in the F₁ rice, which may contribute to the increase in CER. Chlorophyll content (Ch1), soluble protein content (SPC) and ribulose 1,5-bisphosphate (RuBP) carboxylase activity (RCA) were measured as the internal factors related to photosynthesis, and compared between the F₁, rice and the parents. For all these factors, the F₁ rice showed low values compared to the parents. Positive heterosis was not expressed here. On the other hand, the specific activity of RCA (RCA/SPC) increased in the F₁, rice, showing a 120% heterosis effect. This may be regarded as one of the main causes for the increase in CER of the F₁, rice. High CER expressed as heterosis concurrently with large leaf area production is one of the important findings in our study, and this may suggest a high possibility of further improvement in biomass production or yield of rice by gathering the advantageous elements into a hybrid plant.