Populus alba (silver-leaf poplar).

P. alba, the white or silver-leaved poplar, is widely grown as an ornamental for its silvery foliage. It is a fast-growing tree utilized in afforestation and reforestation due to its resistance to drought, salt and wood borers. It is not as important commercially as poplar species of sect. Aigeiros, but its adaptation to warm conditions allows it to be cultivated in Mediterranean regions and in Central Asia. P. alba is widely used in interspecific breeding programmes to introduce valuable traits, such as high rooting ability of stem cuttings, into economically more valuable species, particularly P. tremula of sect. Populus. P. alba hybridizes readily with this closely related species, the resulting hybrid, known as grey poplar (Populus x canescens), being intermediate morphologically between its parents, with a thin, grey, downy coating on the leaves, which are also much less deeply lobed than in white poplar. It exhibits marked hybrid vigour, with trees displaying vigorous growth and reaching 40 m in height and over 1.5 m in trunk diameter, much larger than either of its parents.P. alba is suitable for propagation by tissue culture and is used as a subject for Agrobacterium-mediated genetic transformation.

Comparative Dissection of Three Giant Genomes: Allium cepa, Allium sativum, and Allium ursinum

Knowledge of the fascinating world of DNA repeats is continuously being enriched by newly identified elements and their hypothetical or well-established biological relevance. Genomic approaches can be used for comparative studies of major repeats in any group of genomes, regardless of their size and complexity. Such studies are particularly fruitful in large genomes, and useful mainly in crop plants where they provide a rich source of molecular markers or information on indispensable genomic components (e.g., telomeres, centromeres, or ribosomal RNA genes). Surprisingly, in Allium species, a comprehensive comparative study of repeats is lacking. Here we provide such a study of two economically important species, Allium cepa (onion), and A. sativum (garlic), and their distantly related A. ursinum (wild garlic). We present an overview and classification of major repeats in these species and have paid specific attention to sequence conservation and copy numbers of major representatives in each type of repeat, including retrotransposons, rDNA, or newly identified satellite sequences. Prevailing repeats in all three studied species belonged to Ty3/gypsy elements, however they significantly diverged and we did not detect them in common clusters in comparative analysis. Actually, only a low number of clusters was shared by all three species. Such conserved repeats were for example 5S and 45S rDNA genes and surprisingly a specific and quite rare Ty1/copia lineage. Species-specific long satellites were found mainly in A. cepa and A. sativum. We also show in situ localization of selected repeats that could potentially be applicable as chromosomal markers, e.g., in interspecific breeding.

The Power of Genomic in situ Hybridization (GISH) in Interspecific Breeding of Bulb Onion (Allium cepa L.) Resistant to Downy Mildew (Peronospora destructor [Berk.] Casp.)

We exploited the advantages of genomic in situ hybridization (GISH) to monitor the introgression process at the chromosome level using a simple and robust molecular marker in the interspecific breeding of bulb onion (Allium cepa L.) that is resistant to downy mildew. Downy mildew (Peronospora destructor [Berk.] Casp.) is the most destructive fungal disease for bulb onions. With the application of genomic in situ hybridization (GISH) and previously developed DMR1 marker, homozygous introgression lines that are resistant to downy mildew were successfully produced in a rather short breeding time. Considering that the bulb onion is a biennial plant, it took seven years from the F1 hybrid production to the creation of S2BC2 homozygous lines that are resistant to downy mildew. Using GISH, it was shown that three progeny plants of S2BC2 possessed an A. roylei homozygous fragment in the distal region of the long arm of chromosomes 3 in an A. cepa genetic background. Previously, it was hypothesized that a lethal gene(s) was linked to the downy mildew resistance gene. With the molecular cytogenetic approach, we physically mapped more precisely the lethal gene(s) using the homozygous introgression lines that differed in the size of the A. roylei fragments on chromosome 3.

Production of Interspecific Hybrids between Hydrangea macrophylla and Hydrangea arborescens via Ovary Culture

Hydrangea macrophylla is the most popular species in the genus Hydrangea because of its large and brightly colored inflorescences. Since the early 1900s, numerous cultivars with showy flowers have been selected. Although many H. macrophylla cultivars have been developed, cold hardiness is still the major limitation to their outdoor use. Hydrangea arborescens is a small attractive shrub or subshrub native to northeastern parts of the United States, which is valued for its hardiness. Interspecific breeding of H. arborescens and H. macrophylla has been tried, but putative hybrid seedlings either died at an early stage or were not verified. We made successful hybridizations between H. macrophylla ‘Blue Diamond’ and H. arborescens ‘Annabelle’ and used in vitro ovary culture to produce viable plants. Hybrids were intermediate in appearance between parents, but variable in leaves, inflorescences, and flower color. The success of this hybridization was confirmed by six simple sequence repeat (SSR) genetic markers. The maternal chromosome number was 36, and the paternal number was 38. Chromosome counts of hybrids indicated that nearly half of them were aneuploids. Male fertility of progeny was evaluated by fluorescein diacetate staining of pollen. Twelve out of 14 hybrids (85.7%) had male fertility. We documented the first flowering progeny of H. macrophylla and H. arborescens, suggesting an effective beginning to a cold hardiness breeding program.

Rare interspecific breeding in Pseudo-nitzschia (Bacillariophyceae)

The biological species concept defines species based on sexual incompatibility between strains and the F1 sub-viability or inviability. However, to date, there is only a limited number of studies that formally deal with sexual incompatibility in unicellular protists and hence the rigorous application of biological species concept is fuzzy in these organisms. Here, we investigated interbreeding between two species of the planktonic pennate diatom Pseudo-nitzschia, P. arenysensis and P. pseudodelicatissima. We observed hybridization between these two species in controlled laboratory condition. The F1 generation showed: i) low viability; ii) morphological, ultrastructural, and morphometric features that resembled those of one of the parental strains (P. pseudodelicatissima); iii) intermediate maximum cell size to the one observed in intraspecific sexual crosses in the parental species. Our results may suggest that interbreeding between these two species is possible although likely rare. We invite a larger body of experimental evidence in unicellular protists to assess the applicability of the biological species concept to these organisms.

Gamete and recurrent selection for improving physiological resistance to white mold in common bean

White mold (WM) is a widely distributed and severe disease of common bean in North America. The objective of this study was to determine the effectiveness of gamete (GS) and recurrent (RS) selection methods for improving WM resistance. Two double-crosses, namely USPT-WM-1/CORNELL 601//USPT-CBB-1/92BG-7 and ‘Chas’/I 9365-25//ABL 15/A 195 were made. Equal numbers of progenies from both crosses were subjected to GS and RS. The GS was practiced from F1 to F4 by selecting WM resistant single plants followed by progeny testing in the subsequent generation. Two cycles of RS were practiced by intermating selected WM resistant plants in each cycle. Thirteen selected families in each method and parents were evaluated at 16, 23, and 33 days post first inoculation in replicated trials in two greenhouse environments. Higher frequencies of families with lower WM scores were obtained from GS than RS. The average genetic gains due to GS and RS were 19.6 and 7.9%, respectively. Employing multiple-parent-crosses involving parents of diverse evolutionary origins delayed WM evaluation, and application of GS are recommended for improving physiological WM resistance in common bean.Key words: Interspecific breeding line, introgressing resistance, multiple-parent crosses, Phaseolus vulgaris, pyramiding resistance, Sclerotinia sclerotiorum