Twelve accessions of Triticum tauschii (Coss.) Schmal. were genetically analyzed for resistance to leaf rust (Puccinia recondita Rob. ex Desm.) and stem rust (Puccinia graminis Pers. f.sp. tritici Eriks. and E. Henn.) of common wheat (Triticum aestivum L.). Four genes conferring seedling resistance to leaf rust, one gene conferring seedling resistance to stem rust, and one gene conferring adult-plant resistance to stem rust were identified. These genes were genetically distinct from genes previously transferred to common wheat from T. tauschii and conferred resistance to a broad spectrum of pathogen races. Two of the four seedling leaf rust resistance genes were not expressed in synthetic hexaploids, produced by combining tetraploid wheat with the resistant T. tauschii accessions, probably owing to the action of one or more intergenomic suppressor loci on the A or B genome. The other two seedling leaf rust resistance genes were expressed at the hexaploid level as effectively as in the source diploids. One gene was mapped to the short arm of chromosome 2D more than 50 cM from the centromere and the other was mapped to chromosome 5D. Suppression of seedling resistance to leaf rust in synthetic hexaploids derived from three accessions of T. tauschii allowed the detection of three different genes conferring adult-plant resistance to a broad spectrum of leaf rust races. The gene for seedling resistance to stem rust was mapped to chromosome ID. The degree of expression of this gene at the hexaploid level was dependent on the genetic background in which it occurred and on environmental conditions. The expression of the adult-plant gene for resistance to stem rust was slightly diminished in hexaploids. The production of synthetic hexaploids was determined to be the most efficient and flexible method for transferring genes from T. tauschii to T. aestivum, but crossing success was determined by the genotypes of both parents. Although more laborious, the direct introgression method of crossing hexaploid wheat with T. tauschii has the advantages of enabling selection for maximum expression of resistance in the background hexaploid genotype and gene transfer into an agronomically superior cultivar.

Sectioned and intact shoot apices from Potentilla fruticosa L. plants producing singe and double flowers were examined using optical and scanning electron microscopy. In both flower types the whorls of floral organs were initiated in a helical pattern similar to that of the foliage leaves, although the interval between successive primordia was decreased. The petals and stamens were initiated on a pentagonal ridge surrounding the apex. A primordium was initiated at each vertex of this ridge and about five others along each side. Initially there were no apparent differences among these primordia. The primordia at the vertices always developed into petals. In single flowers all other primordia on the ridge developed into stamens. In double flowers the primordia adjacent to those at the vertices developed petalloid characteristics in the same sequence in which they were initiated. The extra petals are thus found in positions otherwise occupied by stamens, and form at the expense of stamens. Quantitative analysis of petal and stamen numbers support this conclusion.

Total genomic DNA of 27 accessions representing six Aegilops species was restricted with BamHI, EcoRI, and BamHI plus EcoRI, and the restriction fragments were probed with the ribosomal clones pMF2 containing the ribosomal RNA coding regions. The rDNA repeat lengths varied between 9.0 and 10.8 kb. Intraspecific variation among the 10 accessions of Ae. squarrosa var. strangulata ranged from 9.0 to 9.6 kb, suggesting a diversity of genotypes within as well as between species. These variations were not related to their geographical distributions. Each of 24 accessions had two BamHI sites in the coding region (type A), while three accessions of Ae. squarrosa var. strangulata had four BamHI sites (type B, two sites in the intergenic region). Results for these three accessions of Ae. squarrosa var. strangulata suggest genotypic diversity in this species. In BamHI restriction of each accession, a third DNA fragment, ranging between 9.0 and 10.8 kb in type A and 6.0 kb in type B, resulted from lack of digestion at the 26S BamHI site. In double digestion, all rDNA repeat units were restricted by EcoRI, yielding 3.9-, 0.9-, and 4.8-kb fragments, the last of which arose from the lack of digestion at the 26S BamHI site, estimated to occur in 5–20% of the repeat units, depending on the accession.Key words: Triticum tauschii, RFLP, diversity.

The self-incompatibility system in Potentilla fruticosa was investigated by examining pollen cytology, and by analysing intercrosses between two self-incompatible, cross-compatible cultivars of the species. The pollen was found to be binucleate, which is consistent with a single locus self-incompatibility system acting gametophytically in the pollen. This was confirmed by the results of the intercrosses. A proposed model for the inheritance of extra petals was tested by backcrossing selected F1 hybrid plants to both of their parents. Non-random segregation of the double modifier (Dm) locus suggested linkage to the self-incompatibility locus (S). The model was accordingly modified to include this linkage.