Molecular characterization of proliferating carnation plant tissues revealed association with a pararetroviroid-like agent. Carnation small virod-like RNA termed as CarSV RNA is unique among plant viroidlike RNA s by having a homologous DNA counterpart in the plant genome. Previously, CarSV DNA related sequences had been detected in the plant genome fused to microsatellite-like genomic sequences. Here we present data that tissue proliferation symptoms can be seen only on those plants that are expressing the RNA form of this agent. As CarSV RNA adopts a hammerhead structure in both polarities and the plant genome naturally encodes a functional hammerhead ribozyme, it can be concluded that these ribozyme sequences are cleaved out from the plant genome. This could lead to the evolution of small RNA s that replicate autonomously by the rolling circle mechanism and later could spread horizontally by vegetative propagation of the plant material, or by using a hitchhiked plant pararetrovirus fused to its genome.
Authors:E. Nagy, G. Gyulai, Z. Szabó, Z. Hegyi, and L. C. Marton
Studies involving morphological description with both dominant (RAPD) and codominant (SSR, isoenzyme) molecular markers were made on 28 maize inbred lines of known genetic background with a final aim of prediction of heterosis. The genetic distance and degree of relationship between the lines was determined using cluster analysis. Only a very limited extent of allele polymorphism could be detected in isoenzyme analyses as the 28 lines formed only 16 gel electrophoretic groups, indicating that certain lines had identical isoenzyme patterns. On the basis of RAPD and gene-specific microsatellite (SSR) markers, however, all the lines could be distinguished from each other. When the lines were grouped according to genetic background it was found that although the individual marker systems only partially reflected the actual relationships between the lines, a joint processing of the data, supplemented with morphological data, revealed a close correlation between the groups formed on the dendrogram and the genetic background.
Authors:M. Sivasamy, M. Aparna, J. Kumar, P. Jayaprakash, V. Vikas, P. John, R. Nisha, Satyaprakash, K. Sivan, and E. Punniakotti
Nearly twenty thousand wheat lines were phenotyped for the presence of leaf tip necrosis (LTN), a phenotypic trait linked to adult plant leaf rust resistance (APR) genes, viz. Lr34, Lr46 and Lr67 having pleiotropic association with multiple disease resistance genes. Thirty-six lines showed varied expression of LTN and moderate level of leaf rust severity at adult plant stage with slow rusting (disease progress at a retarded rate). Seedling resistance test (SRT) revealed susceptible and mixed infection types, a characteristic of adult plant resistance (APR) genes. Further molecular confirmation for the presence of these genes using available microsatellite markers revealed that of the 36 lines, five lines carried Lr46+ alone and five other lines carried Lr67+ alone. Seven lines carried the combination of Lr34+ and Lr67+ while six lines confirmed to carry the combination of Lr46+ and Lr67+. Remarkably three lines carried all the three APR genes, viz. Lr34+, Lr46+ and Lr67+. All these stocks can be a source of APR multiple disease resistance genes. Ten lines were not confirmed to carry any of the genes but still had LTN and SRT results showing an infection type typical of APR genes and these can be the source of identifying newer APR genes. The resistance based on minor APR genes when combined with a few additional minor genes in the background of high yielding cultivars is expected to have high level of race non-specific resistance and to be durable.
Authors:R. Singh, P. Hucl, M. Båga, and R. Chibbar
Pre-harvest sprouting (PHS) in bread wheat (Triticum aestivum L.) is one of the major abiotic constraints influencing production of high quality grain. Selection for pre-harvest sprouting (PHS) resistance in bread wheat (Triticum aestivum L.) in early generations is difficult because it is expressed as a quantitatively inherited trait and subject to environmental effects. The objectives of this study were to validate a major quantitative trait locus (QTL) for PHS resistance on chromosome 4A in bread wheat and to isolate near-isogenic lines for this QTL using marker-assisted selection. A total of 60 Canadian wheat cultivars and experimental lines were screened with three SSR markers in a QTL region for PHS resistance. The SSR markers DuPw004, barc170 and wmc650 explained 67%, 75% and 60% of total variation in germination (%), respectively, among different wheat genotypes. Marker assisted back crossing with DuPw004 reduced the population size in BC1F1 and BC2F1 generation by 41% and 59%, respectively. A survey of pedigrees of different genotypes revealed that the parental line RL4137 is a major source of increased PHS resistance in a number of western Canadian wheat cultivars. Microsatellite markers (DuPw004, barc170 and wmc650) will be useful for plant breeders to pyramid QTL from different PHS resistance sources.
Authors:Z. Jurković, K. Dugalić, M. Viljevac, I. Piližota, A. Vokurka, B. Puškar, and I. Pejić
Cipriani, G., Lot, G., Huang, W. G., Marrazzo, M. T., Peterlunger, E., Testolin, R. (1999): AC/GT and AG/CT microsatellite repeats in peach [
(L.) Batsch]: isolation, characterisation and cross-species amplification in