Alien chromosome segment from Aegilops speltoides and Dasypyrum villosum increases drought tolerance in wheat via profuse and deep root system.

BACKGROUND: Recurrent drought associated with climate change is a major constraint to wheat (Triticum aestivum L.) productivity. This study aimed to (i) quantify the effects of addition/substitution/translocation of chromosome segments from wild relatives of wheat on the root, physiological and yield traits of hexaploid wheat under drought, and (ii) understand the mechanism(s) associated with drought tolerance or susceptibility in wheat-alien chromosome lines. METHODS: A set of 48 wheat-alien chromosome lines (addition/substitution/translocation lines) with Chinese Spring background were used. Seedling root traits were studied on solid agar medium. To understand the influence of drought on the root system of adult plants, these 48 lines were grown in 150-cm columns for 65 d under full irrigation or withholding water for 58 d. To quantify the effect of drought on physiological and yield traits, the 48 lines were grown in pots under full irrigation until anthesis; after that, half of the plants were drought stressed by withholding water for 16 d before recording physiological and yield-associated traits. RESULTS: The alien chromosome lines exhibited altered root architecture and decreased photochemical efficiency and seed yield and its components under drought. The wheat-alien chromosome lines T5DS·5S#3L (TA5088) with a chromosome segment from Aegilops speltoides (5S) and T5DL.5 V#3S (TA5638) with a chromosome segment from Dasypyrum villosum (5 V) were identified as drought tolerant, and the drought tolerance mechanism was associated with a deep, thin and profuse root system. CONCLUSIONS: The two germplasm lines (TA5088 and TA5638) could be used in wheat breeding programs to improve drought tolerance in wheat and understand the underlying molecular genetic mechanisms of root architecture and drought tolerance.

Co-existence of Leclercia adecarboxylata (LSE-1) and Bradyrhizobium sp. (LSBR-3) in nodule niche for multifaceted effects and profitability in soybean production.

The present study was designed with the objective of improving growth and nodulation of soybean [Glycine max (L.) Merill] with co-inoculation of native Bradyrhizobium sp. (LSBR-3) (KF906140) and non-rhizobial nodule endophytic diazotroph Leclercia adecarboxylata (LSE-1) (KX925974) with multifunctional plant growth promoting (PGP) traits in cereal based cropping system (Rice-Wheat). A total of 40 endophytic bacteria from cultivated and wild sp. of soybean were screened for multifarious PGP traits and pathogenicity test. Based on PGP traits, antagonistic activities and bio-safety test; L. adecarboxylata (LSE-1) was identified with 16 S rRNA gene sequencing along with the presence of nifH (nitrogen fixation) and ipdc (IAA production) genes. Dual inoculant LSE-1 and LSBR-3 increased indole acetic acid (IAA), P & Zn-solubilization, 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity, siderophore, biofilm formation and exo-polysaccharides in contrast to single inoculation treatment. Further, assessment of dual inoculant LSBR-3 + LSE-1 improved growth parameters, nodulation, soil enzymes activities, nutrient accumulation and yield as compared to single as well as un-inoculated control treatment under field conditions. Single inoculant LSBR-3 improved yield by 8.84% over control. Further, enhancement of 4.15% grain yield was noticed with LSBR-3 + LSE-1 over LSBR-3 alone treatment. Application of LSBR-3 + LSE-1 gave superior B:C ratio (1.29) and additional income approximately 116 USD ha-1 in contrast to control treatment. The present results thus, is the first report of novel endophytic diazotroph L. adecarboxylata (LSE-1) as PGPR from Indian conditions particularly in Punjab region for exploiting as potential PGPR along with Bradyrhizobium sp. (LSBR-3) in soybean.

Synergism of Pseudomonas aeruginosa (LSE-2) nodule endophyte with Bradyrhizobium sp. (LSBR-3) for improving plant growth, nutrient acquisition and soil health in soybean.

The present study was aimed to assess the scope of native potential endophyte Pseudomonas aeruginosa (LSE-2) strain (KX925973) with recommended Bradyrhizobium sp. (LSBR-3) (KF906140) for synergistic effect to develop as consortium biofertilizer of soybean. A total of 28 non-rhizobial endophytic bacteria were isolated from cultivated and wild sp. of soybean. All isolates were screened for multifarious PGP traits viz. Indole-3-acetic acid (IAA), phosphate (P) and zinc (Zn) solubilization, siderophore, cell wall degrading enzymes and pathogenicity. Compatible of LSBR-3 and LSE-2 enhanced IAA, P-solubilization, 1-aminocyclopropane-carboxylate deaminase and biofilm formation over the single inoculant treatment. Further, consortium was evaluated in vivo for growth, symbiotic traits, nutrient acquisition, soil quality parameters and yield attributes of soybean. Improvement in growth parameters were recorded with dual inoculant LSBR-3 + LSE-2 as compared to LSBR-3 alone and un-inoculated control treatments. Significantly (p ≥ 0.05) high symbiotic and soil quality parameters (phosphatase and soil dehydrogenase activity) was recorded with LSBR-3 + LSE-2 at vegetative and flowering stage as compared to LSBR-3 alone and un-inoculated control treatments. Single inoculation of LSBR-3 improved grain yield by 4.25% over the un-inoculated control treatment, further, enhancement in yield was recorded with consortium inoculant (LSBR-3 and LSE-2) by 3.47% over the LSBR-3 alone. Application of consortium inoculant (LSBR-3 + LSE-2) gave an additional income of Rs. 5089/ha over the un-inoculated control treatment. The results, thus strongly suggest that endophytic diazotroph LSE-2 can be used as potent bio-inoculant along with LSBR-3 as bio-enhancer for improving soybean productivity in a sustainable system.

Multiplate and TEG platelet mapping in a population of severely injured trauma patients.

OBJECTIVES: The objectives of this study were to compare thromboelastography platelet mapping (TEG PM) with impedance aggregometry (Multiplate, MP) in a single trauma population and relate their results clinically. BACKGROUND: Platelet function as measured by thromboelastography and impedance aggregometry demonstrates significant reductions that persist for days following traumatic injury. However, no study compares these devices and the correlation between them is not known. METHODS: In level 1 trauma patients, TEG PM and MP were conducted at their initial presentation to the emergency department. Within-device repeatability and between-device association were determined using correlation analyses. Demographic variables, Injury Severity Score, blood product transfusion, laboratory test results and mortality rate were recorded. RESULTS: Ninety-two patients were enrolled. Within-device repeatability was high for TEG PM and MP for arachidonic acid (AA) and adenosine diphosphate (ADP) activation pathways. When comparing TEG PM with MP, results correlated poorly in the ADP pathway (Spearman's rho = 0·11, P = 0·44) and moderately in the AA pathway (Spearman's rho = 0·56, P < 0·0001). TEG PM was predictive of blood product transfusion and correlated with increased base deficit, whereas MP was only predictive of mortality. CONCLUSIONS: Intra-device variability was low for TEG PM and MP, but the two point-of-care devices measuring platelet function correlate poorly with each other in injured trauma patients. Each device also had different clinical associations.

Linkage mapping of Mungbean yellow mosaic India virus (MYMIV) resistance gene in soybean.

Mungbean Yellow Mosaic India Virus (MYMIV) is one of the most prevalent pathogen that limits soybean production in India. In this study RILs derived from JS335, dominant but MYMIV susceptible variety and PI171443, donor of MYMIV resistance gene in most of the MYMIV resistant varieties released in India and F2 population derived from SL525, a resistant variety released for northern India and NRC101, a susceptible genotype were used to study the inheritance of MYMIV resistance and map the gene responsible for MYMIV resistance. F1s were found to be completely susceptible. F2:3 and RILs population segregated to fit a ratio of 1:2:1 and 1:1 indicating that a single recessive gene controlled resistance to MYMIV. BSA was performed using 144 polymorphic SSR markers. MYMIV resistance gene was mapped on chr 6 (LG C2) within a 3.5-cM genome region between two SSR markers GMAC7L and Satt322 whose size was estimated to be 77.115 kb (position of 12,259,594-12,336,709 bp). This is the first report on linkage mapping of MYMIV resistance gene in soybean. This will be helpful in breeding soybean varieties for resistance against MYMIV responsible for wide spread damage to soybean crop in India using Marker Assisted Selection.

Testing the impact of virus importation rates and future climate change on dengue activity in Malaysia using a mechanistic entomology and disease model.

We aimed to reparameterize and validate an existing dengue model, comprising an entomological component (CIMSiM) and a disease component (DENSiM) for application in Malaysia. With the model we aimed to measure the effect of importation rate on dengue incidence, and to determine the potential impact of moderate climate change (a 1 °C temperature increase) on dengue activity. Dengue models (comprising CIMSiM and DENSiM) were reparameterized for a simulated Malaysian village of 10 000 people, and validated against monthly dengue case data from the district of Petaling Jaya in the state of Selangor. Simulations were also performed for 2008-2012 for variable virus importation rates (ranging from 1 to 25 per week) and dengue incidence determined. Dengue incidence in the period 2010-2012 was modelled, twice, with observed daily weather and with a 1 °C increase, the latter to simulate moderate climate change. Strong concordance between simulated and observed monthly dengue cases was observed (up to r = 0·72). There was a linear relationship between importation and incidence. However, a doubling of dengue importation did not equate to a doubling of dengue activity. The largest individual dengue outbreak was observed with the lowest dengue importation rate. Moderate climate change resulted in an overall decrease in dengue activity over a 3-year period, linked to high human seroprevalence early on in the simulation. Our results suggest that moderate reductions in importation with control programmes may not reduce the frequency of large outbreaks. Moderate increases in temperature do not necessarily lead to greater dengue incidence.

Sequence organization and evolutionary dynamics of Brachypodium-specific centromere retrotransposons.

Brachypodium distachyon is a wild annual grass belonging to the Pooideae, more closely related to wheat, barley, and forage grasses than rice and maize. As an experimental model, the completed genome sequence of B. distachyon provides a unique opportunity to study centromere evolution during the speciation of grasses. Centromeric satellite sequences have been identified in B. distachyon, but little is known about centromeric retrotransposons in this species. In the present study, bacterial artificial chromosome (BAC)-fluorescence in situ hybridization was conducted in maize, rice, barley, wheat, and rye using B. distachyon (Bd) centromere-specific BAC clones. Eight Bd centromeric BAC clones gave no detectable fluorescence in situ hybridization (FISH) signals on the chromosomes of rice and maize, and three of them also did not yield any FISH signals in barley, wheat, and rye. In addition, four of five Triticeae centromeric BAC clones did not hybridize to the B. distachyon centromeres, implying certain unique features of Brachypodium centromeres. Analysis of Brachypodium centromeric BAC sequences identified a long terminal repeat (LTR)-centromere retrotransposon of B. distachyon (CRBd1). This element was found in high copy number accounting for 1.6 % of the B. distachyon genome, and is enriched in Brachypodium centromeric regions. CRBd1 accumulated in active centromeres, but was lost from inactive ones. The LTR of CRBd1 appears to be specific to B. distachyon centromeres. These results reveal different evolutionary events of this retrotransposon family across grass species.

Physical characteristics and nutritional composition of some new soybean (Glycine max (L.) Merrill) genotypes.

Soybean is a major source of high quality protein and oil and soybean seed quality is often determined by seed nutritional and antinutritional parameters. The objective of this study was to investigate the physical characteristics and nutritional composition of some new soybean genotypes. Hundred seed weight and volume of soybean genotypes ranged from 8.7 to 11.1 g and 8.1 to 12.0 ml respectively, whereas, percent water absorption and percent volume expansion values ranged from 94.3 to 119.5% and 70.8 to 159.5% respectively. The genotypes contained % crude protein (39.4-44.4), oil (14.0-18.7), starch (4.3-6.7), total soluble sugars (5.6-7.9), reducing sugars (0.21-0.33) and sucrose (5.6-11.8). The free fatty acid and triglyceride content ranged from 31-71 mg 100 g(-1) oil and 90.1-93.9 g 100 g(-1) oil respectively. The antinutritional components determined include: mg g(-1) TIA (41.5-85.0), phytate (2.3-5.6), total phenols (1.0-1.5), flavonols (0.20-0.34) and ortho-dihydroxy phenols (0.10-0.21). A significant variation for the 11S/7S ratio was observed among the 8 soybean genotypes and the values ranged from 0.70 ('SL 768' and 'SL 869') to 2.4 ('SL 794').

MRI and PET-CT: Comparison in post-treatment evaluation of head and neck squamous cell carcinomas.

BACKGROUND: Treatment of patients with head and neck cancers includes surgery, radiation therapy and chemotherapy due to which the complex anatomy in this region is further complicated by post surgical or radiation changes making the distinction between post therapy changes and recurrence or residual tumor challenging. We decided to compare the diagnostic performance of FDG-PET/CT and MRI scans in the response assessment of patients with Head and Neck Squamous Cell Carcinomas (HNSCC). METHODS: Fifty consecutive patients with carcinoma of the head and neck region undergoing treatment at our center were enrolled in the study and evaluated with both MRI scan and PET-CT scan at presentation, at 12 weeks after treatment and at 24 weeks post-treatment. RESULTS: Post treatment evaluation at 24 weeks revealed a sensitivity, specificity, PPV, NPV of 95.83%, 82.37%, 78.91%, 96.3% for MRI respectively while corresponding values for PET-CT scans were 95.83%, 91.97%, 85.45% and 96.3%. Evaluation by treatment modality showed a concurrence rate of positive biopsies of 71.33% and 74.54% respectively for MRI and PET-CT scans in surgical patients, 93.33% and 91.25% respectively for the chemo-radiotherapy and 71.43% and 85.71% respectively for patients treated with surgery and radiotherapy. CONCLUSION: In our study, both modalities were useful for evaluation at 12 weeks, however by 24 weeks PET-CT was superior. Both the modalities suffer from high negative predictive values and relatively low positive predictive values. These persisted irrespective of the treatment modality with MRI being slightly better for patients on chemo-radiotherapy while PET-CT scans were better if surgery was one of the modalities of treatment.

Genome comparisons reveal a dominant mechanism of chromosome number reduction in grasses and accelerated genome evolution in Triticeae.

Single-nucleotide polymorphism was used in the construction of an expressed sequence tag map of Aegilops tauschii, the diploid source of the wheat D genome. Comparisons of the map with the rice and sorghum genome sequences revealed 50 inversions and translocations; 2, 8, and 40 were assigned respectively to the rice, sorghum, and Ae. tauschii lineages, showing greatly accelerated genome evolution in the large Triticeae genomes. The reduction of the basic chromosome number from 12 to 7 in the Triticeae has taken place by a process during which an entire chromosome is inserted by its telomeres into a break in the centromeric region of another chromosome. The original centromere-telomere polarity of the chromosome arms is maintained in the new chromosome. An intrachromosomal telomere-telomere fusion resulting in a pericentric translocation of a chromosome segment or an entire arm accompanied or preceded the chromosome insertion in some instances. Insertional dysploidy has been recorded in three grass subfamilies and appears to be the dominant mechanism of basic chromosome number reduction in grasses. A total of 64% and 66% of Ae. tauschii genes were syntenic with sorghum and rice genes, respectively. Synteny was reduced in the vicinity of the termini of modern Ae. tauschii chromosomes but not in the vicinity of the ancient termini embedded in the Ae. tauschii chromosomes, suggesting that the dependence of synteny erosion on gene location along the centromere-telomere axis either evolved recently in the Triticeae phylogenetic lineage or its evolution was recently accelerated.

Genetic compensation abilities of Aegilops speltoides chromosomes for homoeologous B-genome chromosomes of polyploid wheat in disomic S(B) chromosome substitution lines.

The S genome of Aegilops speltoides is closely related to the B and G genomes of polyploid wheats. However, little work has been reported on the genetic relationships between the S-genome and B-genome chromosomes of polyploid wheat. Here, we report the isolation of a set of disomic substitutions (DS) of S-genome chromosomes for the B-genome chromosomes and their effects on gametophytic and sporophytic development. Ae. speltoides chromosomes were identified by their distinct C-banding and fluorescence in situ hybridization patterns with the Ae. speltoides-derived clone pGc1R-1. Although no large structural differences between S-genome and B-genome chromosomes exist, significant differences in gametophytic compensation were observed for chromosomes 1S, 3S, 5S and 6S. Similarly, chromosomes 1S, 2S, 4S, 5S and 6S affected certain aspects of sporophytic development in relation to spike morphology, fertility and meiotic pairing. The DS5S(5B) had disturbed meiosis with univalents/multivalents and suffered chromosome elimination in the germ tissues leading to haploid spikes in 50% of the plants. The effect of the Ph1 gene on meiosis is well known, and these results provide evidence for the role of Ph1 in the maintenance of polyploid genome integrity. These and other data are discussed in relation to the structural and functional differentiation of S- and B-genome chromosomes and the practical utility of the stocks in wheat improvement.

A novel Robertsonian translocation event leads to transfer of a stem rust resistance gene (Sr52) effective against race Ug99 from Dasypyrum villosum into bread wheat.

Stem rust (Puccinia graminis f. sp. tritici Eriks. & E. Henn.) (the causal agent of wheat stem rust) race Ug99 (also designated TTKSK) and its derivatives have defeated several important stem rust resistance genes widely used in wheat (Triticum aestivum L.) production, rendering much of the worldwide wheat acreage susceptible. In order to identify new resistance sources, a large collection of wheat relatives and genetic stocks maintained at the Wheat Genetic and Genomic Resources Center was screened. The results revealed that most accessions of the diploid relative Dasypyrum villosum (L.) Candargy were highly resistant. The screening of a set of wheat-D. villosum chromosome addition lines revealed that the wheat-D. villosum disomic addition line DA6V#3 was moderately resistant to race Ug99. The objective of the present study was to produce and characterize compensating wheat-D. villosum whole arm Robertsonian translocations (RobTs) involving chromosomes 6D of wheat and 6V#3 of D. villosum through the mechanism of centric breakage-fusion. Seven 6V#3-specific EST-STS markers were developed for screening F(2) progeny derived from plants double-monosomic for chromosomes 6D and 6V#3. Surprisingly, although 6D was the target chromosome, all recovered RobTs involved chromosome 6A implying a novel mechanism for the origin of RobTs. Homozygous translocations (T6AS·6V#3L and T6AL·6V#3S) with good plant vigor and full fertility were selected from F(3) families. A stem rust resistance gene was mapped to the long arm 6V#3L in T6AS·6V#3L and was designated as Sr52. Sr52 is temperature-sensitive and is most effective at 16°C, partially effective at 24°C, and ineffective at 28°C. The T6AS·6V#3L stock is a new source of resistance to Ug99, is cytogenetically stable, and may be useful in wheat improvement.

Identification of stable heat tolerance QTLs using inter-specific recombinant inbred line population derived from GPF 2 and ILWC 292.

Heat stress during reproductive stages has been leading to significant yield losses in chickpea (Cicer arietinum L.). With an aim of identifying the genomic regions or QTLs responsible for heat tolerance, 187 F8 recombinant inbred lines (RILs) derived from the cross GPF 2 (heat tolerant) × ILWC 292 (heat sensitive) were evaluated under late-sown irrigated (January-May) and timely-sown irrigated environments (November-April) at Ludhiana and Faridkot in Punjab, India for 13 heat tolerance related traits. The pooled ANOVA for both locations for the traits namely days to germination (DG), days to flowering initiation (DFI), days to 50% flowering (DFF), days to 100% flowering (DHF), plant height (PH), pods per plant (NPP), biomass (BIO), grain yield (YLD), 100-seed weight (HSW), harvest index (HI), membrane permeability index (MPI), relative leaf water content (RLWC) and pollen viability (PV)) showed a highly significant difference in RILs. The phenotyping data coupled with the genetic map comprising of 1365 ddRAD-Seq based SNP markers were used for identifying the QTLs for heat tolerance. Composite interval mapping provided a total of 28 and 23 QTLs, respectively at Ludhiana and Faridkot locations. Of these, 13 consensus QTLs for DG, DFI, DFF, DHF, PH, YLD, and MPI have been identified at both locations. Four QTL clusters containing QTLs for multiple traits were identified on the same genomic region at both locations. Stable QTLs for days to flowering can be one of the major factors for providing heat tolerance as early flowering has an advantage of more seed setting due to a comparatively longer reproductive period. Identified QTLs can be used in genomics-assisted breeding to develop heat stress-tolerant high yielding chickpea cultivars.

Inheritance and biochemical basis of yellowing of apical leaves: a unique trait in chickpea (Cicer arietinum L.).

A unique trait, i.e. yellowing of apical/young leaves in response to low temperature and high relative humidity was identified in a chickpea genotype, ICCX110069. To determine inheritance pattern of this trait, ICCX110069 was crossed to four other genotypes, GL14050, GL14049, GL14059 and SAGL152117, that exhibited normal green apical leaves under similar environmental conditions. The F1, F2, F3, BC1F1 and BC1F2 generations were generated. A ratio of 13 normal green leaf: three yellow leaf was found to be the best fit, indicated digenic gene action with suppressor effect of normal green leaf over the expression of yellowing of apical/young leaf trait. The chlorophyll content was significantly lower, while guaiacol peroxidase activity was significantly higher in yellow leaves of ICCX110069 as compared to green leaves of the same genotype and of GL14049, indicating the competence of antioxidative defence mechanism involved with the expression of this trait.

Fate of Aegilops speltoides-derived, repetitive DNA sequences in diploid Aegilops species, wheat-Aegilops amphiploids and derived chromosome addition lines.

The present study reports the cloning and characterization of an Aegilops speltoides-derived subtelomeric repeat, designated as pSp1B16. Clone pSp1B16 has 98% sequence homology with the previously isolated Ae. speltoides repeat Spelt1. The distribution of pSp1B16 and another Ae. speltoides repeat, pGc1R1, was analyzed in diploid Aegilops species, tetra- and hexaploid wheats, wheat-Aegilops amphiploids and derived chromosome addition lines by fluorescence in situ hybridization (FISH). Clones pSp1B16 and pGc1R1 revealed FISH sites in Ae. speltoides, Ae. sharonensis and Triticum timopheevii, whereas additional pGc1R1 FISH sites were observed in Ae. longissima and Ae. caudata. The pSp1B16 and pGc1R1 FISH patterns of the Aegilops chromosomes in the wheat-Aegilops amphiploids and chromosome addition lines are similar to those present in the Aegilops parent accession. We did not observe any evidence of pSp1B16 and pGc1R1 sequence elimination, which is in contrast to previous studies using similar hybrids and repeats. The presented data suggest that the genomic changes in synthetic amphiploids observed in previous studies might be caused by homoeologous recombination, which was suppressed in the amphiploid analyzed in this study.

A population-based cross-sectional study to determine the practices of breastfeeding among the lactating mothers of Patiala city.

INTRODUCTION: The present study was undertaken to study the breastfeeding practices and the influence of literacy and prevailing cultural factors on different aspects of breastfeeding. MATERIALS AND METHODS: A community-based cross-sectional study was conducted at Badungar, a semi-urban area in Patiala city including a total of 370 mothers. Mothers were interviewed using pre-formed, semi-structured Performa. The participant's demographic information, awareness and practices regarding breastfeeding were recorded by paying house to house visits. Data were analyzed using SPSS ver. 21. RESULTS: Only 27.30% of the mothers knew that breastfeeding should be initiated within 1 hour of birth. A total of 51.62% mothers considered prelacteal feed to be the right practice while 55.95% considered colostrum bad for the baby. Only 53.78% of the lactating mothers knew the correct meaning of exclusive breastfeeding. Only 24.86% mothers started breastfeeding within an hour after birth. Colostrum was not given by 57.29% of the lactating mothers while Prelacteal feeds were given by 50.81% mothers. Exclusive breastfeeding till 6 months was given by 45.67% mothers. A significant association was observed in high mother's education, high socio-economic status, nuclear status of family, history of antenatal care registration, and hospital delivery with exclusive breastfeeding (P < 0.01). CONCLUSION: Study concluded that breastfeeding practices were not optimum; hence promotion of knowledge regarding the right practices of breastfeeding and focus on the factors affecting them is highly warranted in this area.

Plant cytogenetics at the dawn of the 21st century.

The years 1996-1997 saw advances in plant chromosome handling, structure, behaviour and manipulation. Improved protocols were developed for flow sorting, microdissection and microcloning. Fibre FISH was used to map a range of DNA sequences at a resolution of a few kilobases. Over 400 wheat deletion stocks were reported and healing of broken chromosomes by de novo addition of telomeric sequences was demonstrated. Centromeric DNA sequences were identified. The role of telomeric ends in pairing was demonstrated. Apparently unusually long chromosome arms can interfere with mitosis. Novel phenomena and potential of wide hybrids for genome analysis were noteworthy.

Robertsonian translocations in wheat arise by centric misdivision of univalents at anaphase I and rejoining of broken centromeres during interkinesis of meiosis II.

The mechanism of origin of Robertsonian translocations was investigated in plants monosomic for chromosome 1A of wheat and 1H(t) of Elymus trachycaulus by GISH. Chromosomes 1A and 1H(t) stayed univalent in all metaphase I cells analyzed, suggesting that Robertsonian translocations do not originate from meiotic recombination in centromeric regions with shared DNA sequence homology. At ana-/telophase I, the 1H(t) and 1A univalents underwent either chromosome or chromatid segregation and misdivided in 6-7% of the pollen mother cells. None of the ana-/telophases I analyzed had Robertsonian translocations, which were only observed in 2% of the "half tetrads" at ana-/telophase II. The frequency of Robertsonian translocations observed at ana-/telophase II corresponds well with the number of Robertsonian translocations (1-4%) detected in progenies derived from plants monosomic for group-1 chromosomes of wheat (1A, 1B, and 1D) and 1H(t) of E. trachycaulus. Our data suggest that Robertsonian translocations arise from centric misdivision of univalents at ana-/telophase I, followed by segregation of the derived telocentric chromosomes to the same nucleus, and fusion of the broken ends during the ensuing interkinesis.

A novel ditertiary tetrasomic in tomato.

Cytogenetic studies were carried out on a ditertiary tetrasomic, 2n + 2 (5L.7S), of tomato (Lycopersicon esculentum Mill.). In studies of transmission of the 5L.7S chromosome, male and female rates of 57.1% and 74.5%, respectively, were found-the highest yet reported for any tomato aneuploid. Additionally, two 5L.7S tertiary chromosomes were transmitted through the female gametophyte, the maximum duplication known to be tolerated by this developmental stage. Monotertiary tetrasomics of a novel type, 2n + 5L.5S + 5L.7S, were recovered in the selfed progeny of 2n + 2(5L.7S). The usefulness of the ditertiary tetrasomic for the production of double trisomics and for dosage and experimental evolutionary studies is elaborated.