Genome classification of banana cultivars from South India using IRAP markers

Summary The banana cultivars are originated from the intra- and inter-specific hybridization of two wild diploid species, Musa acuminata Colla and Musa balbisiana Colla, contributing the A and B genomes, respectively. They are classified into genomic groups by scoring morphological features. Molecular markers provide a quick and reliable system of genome characterization and manipulation in breeding lines. In the present study a PCR based molecular marker specific for B genomes is been reported. The IRAP primer, designed based on the LTR sequence of banana Ty3-gypsy-like retroelement (Musa acuminata Monkey retrotransposon, AF 143332), was used to identify the B genome in the banana cultivars. Further a primer pair designed from B specific bands of Musa balbisiana `Pisang Gala' was used to classify AAB and ABB cultivars in the collection. Among the 36 cultivars tested with this primer, the B specific band was absent in the AA and AAA cultivars (except in one AAA and AAB cultivar) but present in all other AB, AAB and ABB cultivars. Among the triploid AAB/ABB, the PCR products with B specific primers showed restriction pattern polymorphism with AluI. In ABB genomes the band intensity was high whereas low intensity band observed in AAB genomes. Four cultivars reported to have the ABB genome showed a pattern similar to AAB, and one cultivar reported to have AAA genome showed a pattern similar to ABB genome, suggesting missampling or misidentification. The primers used in this study are useful to identify the presence of B genome in banana cultivars, and band intensity may be a preliminary indicator of ploidy level of the B genome but needs further studies with competitive PCR for clarification. These authors contributed equally in this paper.     

Molecular Analysis of Local Potato Cultivars from Tenerife Island Using Microsatellite Markers

We have used 19 SSR markers to fingerprint 41 local potato cultivars from 10 locations of Tenerife Island. These varieties represent relicts of the early introductions originating from South America and have been characterised previously morphologically and ecophysiologically. The SSR primers generated a varying degree of polymorphisms. A total of 67 alleles were observed, 12 of them were present in all cultivars. Several accession and group specific alleles were detected. Similarity coefficients were computed from the molecular data and cluster analyses were performed. Generally, cultivar groups with identical or related common names showed the same SSR patterns or clustered closely together. According to the molecular patterns misleading or confounded names were evident for four accessions. The dendrogram clusters were generally in good agreement with previous classifications of the accessions as Solanum tuberosum subsp. andigena, S. tuberosum subsp. tuberosum and Solanum chaucha genotypes. However in four cases the molecular patterns showed discrepancies with previous species assignments suggesting the need for a more detailed and comparative study of these accessions.     

Recent advances in molecular genetics of forest trees

The use of molecular markers has greatly enhanced our understanding of the genome structure of forest trees. Conifers, in particular, have a relatively large genome, containing a very high proportion of repeated DNA, consisting of tandemly repetitive and dispersed repetitive DNA sequences. The nature of highly conserved tandemly repetitive rRNA genes has been investigated in a number of tree species, and their sites mapped on specific chromosomes by fluorescent in situ hybridization (FISH). Different families of retrotransposons (IFG, and TPE1) have been isolated and characterized from the dispersed repetitive DNA of pines. Genome maps have been constructed in a number of forest tree genera: Pinus, Picea, Pseudotsuga, Cryptomeria, Taxus, Populus, and Eucalyptus. EST databases have been established from cDNA clones of pines and poplars. The structure and maternal or paternal modes of inheritance of organelle genomes have been investigated in forest trees. Comparative mapping in conifers has shown that gene families are conserved across genera. Due to lack of polyploidy in conifers, the evolution of this group of trees may have occurred primarily by duplication and dispersal of genes, probably by retrotranspositions, to form complex gene families. The evolution of angiosperm tree species has presumably involved both gene duplication as well as genome duplication (polyploidy). Application of genetic engineering has shown that genes from phylogenetically unrelated organisms can be introduced and expressed in trees, thus offering prospects of genetic improvement of forest trees. This revised version was published online in August 2006 with corrections to the Cover Date.     

Progress in mapping agronomic genes in apple (The European Apple Genome Mapping Project)

Summary The progress of the European Apple Genome Mapping Project is described. Populations segregating for a range of agronomic genes have been established in six European countries. The need for robust methods of analysis has been identified, especially with regard to the development of molecular markers. Isozyme systems, RAPDs, RFLPs and amplified genes are being used to construct a reference genetic linkage map. Standardisation and precise definition of both genotypic and phenotypic measurements has been recognised as being essential for future exploitation of genetic markers in apple breeding. Phenotypic measurements are being replicated in different geographical locations over several years. Statistical and genetic analyses are aimed at defining components of genetic variation which account for ‘genes’, as defined by apple breeders. A relational database is being constructed which will combine disparate sources of data relating to the genetics of apple. Comparative mapping has been identified as an efficient means of expanding genetic knowledge within and between Rosaceae genomes.     

Selection for Non-Shattering Common Vetch, Vicia sativa L.

Loss of seeds from mature pods is common in Vicia sativa L., an important annual, resown forage legume in West Asia and North Africa. Pod shattering restricts its use as a leguminous forage crop. This paper reports the results of germplasm evaluation for non-shattering pods and of breeding and selection to improve seed retention. Wide variation in pod-shattering exists between common vetch ecotypes collected from different regions. Three wild mutants with almost completely non-shattering pods were identified and isolated for use as a genetic resource in cross breeding programmes. Genetic studies revealed that the non-shattering character in the wild types of common vetch is due to a simple recessive gene, whereas shattering in the cultivated types is due to an allelic dominant pair of genes. Incorporation of the non-shattering gene into agronomically-promising lines was achieved by back-crossing. Lines having an average of 95—97 % non-shattering pods were obtained, as compared to 40—50 % in the original cultivated lines which represents a major agronomic advance in common vetch breeding. The importance of seed retention to the economics of seed production is discussed.     

Use of multiparental inbred populations to determine allelic relationships of molecular markers

The assessment of polymorphism exhibited by molecular markers is an arduous but essential task that facilitates the use of molecular tools by breeders and geneticists. For that purpose, the value of a wheat composite population was assessed for characterizing the diversity of restriction fragment length polymorphism (RFLP) markers developed by INRA-Génoblé. The polymorphism of 13 genomic probes was measured over a set of 80 inbred lines randomly extracted by single-seed descent from a composite-cross of 16 wheat lines. The 13 probéenzyme combinations revealed 27 loci with codominant polymorphism. As many bands were so far unmapped, the segregational analysis of the progenies appeared very suitable for complex patterns, both in determining allelic relationships and in revealing linkage between loci. Allelic diversity, band sizes and chromosomal location assessed from nullisomic-tetrasomic lines are given for the 27 loci.     

Inheritance of new genetic markers in lentil (Lens Miller)

Summary We report on the inheritance of 11 morphological markers and 17 isozymes in lentil (Lens culinaris). The monogenic inheritance of 11 morphological markers and 11 isozymes is confirmed. The inheritance of six isozymes (Aco-2, Enp, Est-3, Est-4, Lap-3, and Mdh-m) is reported for the first time in lentil. This brings the total number of described genes in lentil to 78. Cases of disturbed segregation were more frequent than expected by chance. It is suggested that disturbed segregation was in most cases caused by linkage with a piece of chromosome that showed preferential elimination in crosses between Lens culinaris ssp. odemensis and other subspecies. The prevalence of disturbed segregation in crosses with Lens culinaris ssp. odemensis could limit the usefulness of this subspecies in genetic and linkage studies.     

Inheritance of Induced Morphological Mutants in Triticutn monococcum L.

The mode of inheritance of fifteen induced morphological mutants in diploid wheat Triticum monococcum L. was determined. The results showed that earliness, reduced height, uniculm, liguleless branched spike, compact ear, and free-threshing habit of each of these mutants is the result of a single recessive mutation. Red awns and xantha traits are controlled by two recessive genes with duplicate and inhibitory gene interactions, respectively. Some of the early and dwarf mutants were non-allelic. One dwarf GA₃-insensitive mutant with recessive gene action may be a new source. Mutants such as early maturing, dwarf and free threshing habit may be of significance in breeding diploid wheat.     

Identification of RAPD markers linked to nut weight and plant stature in cashew

Cashew is an important edible nut crop of tropics. Bulk segregant analysis (BSA) was carried out on DNA bulks constituted from F₂ population and germplasm in order to link or associate molecular markers with economic characters. In all 458 RAPD, 31 ISSR and 21 pairs of SSR primers were used and identified polymorphic markers between parents. Though screening F₂ bulks with these markers identified markers polymorphic between the bulks but none could be validated with the individuals of their bulks. Hence screening with germplasm bulks was carried out and could identify four RAPD markers polymorphic between the bulks for nut weight and plant stature and also between the individuals of their bulks. Of the four, three markers were associated with nut weight amplifying at 775, 475, 275, bp region in primers OPN 14, UBC 184 and UBC 185 respectively. Out of these three, two markers were specific to low nut weight and one marker was specific to high nut weight and their bands were present in greater frequency (50–77.8% and 75%) of individuals constituting the respective bulks. Similarly, the another marker UBC 185₂₇₅ was detected which was specific to low plant stature and was present in 66.7% and 10% individuals constituting short and tall bulks respectively. Markers identified with bulks and with the individuals of bulks were validated further with more individuals of F₂ and germplasm.