The mating inter-relationships among Avon Gorge Sorbus taxa are complex and are the driving force for hybridization and ongoing genetic diversification. In particular, the presence of self-incompatibility in triploid pseudogamous apomicts imposes a requirement for interspecific cross-pollination, thereby facilitating continuing diversification and evolution through rare sexual hybridization events. This is the first report of naturally occurring pseudogamous apomictic SI plant populations, and we suggest that interspecific pollination, in combination with a relaxed endosperm balance requirement, is the most likely route to the persistence of these populations. We propose that Avon Gorge Sorbus represents a model system for studying the establishment and persistence of SI apomicts in natural populations.

Vujović T., Ružić Dj., Cerović R., 2012. In vitro shoot multiplication as influenced by repeated subculturing of shoots of contemporary fruit rootstocks. Hort. Sci. (Prague), 39: 101-107.In vitro shoots of vegetative rootstocks for cherry (Gisela 5 and Gisela 6), plum (Fereley Jaspi) and pear (Pyrodwarf ) were repeatedly subcultured for 10 subcultures on Murashige and Skoog medium of unchanged hormonal composition. Shoot formation capacity decreased over repeated subculturing in all genotypes. The first significant decrease in multiplication index was observed after first subculture in Gisela 6 and Fereley Jaspi, while in Gisela 5 the decline occurred after second subculture, and remained at that level. As for Gisela 6 and Fereley Jaspi, multiplication index was mainly stable from second to forth subculture, whereupon the second decline in shoot formation was observed. Although Pyrodwarf showed very low multiplication capacity, shoot multiplication slightly increased over the first three subcultures and then declined. This irreversible decline could be due to residual effects of hormones. However, no visible morphological variations or aberrations of shoots were found in successive subcultures in any genotype. Quality of shoots in terms of shoot length varied during subculturing, but the highest quality was observed in later subcultures (from fifth subculture onwards). After subculturing, several media were evaluated for induction of rhizogenesis in order to achieve high rooting rates in tested rootstocks. The highest rooting ability (100%) among genotypes was observed in Fereley Jaspi, followed by Pyrodwarf and Gisela 6 (the best rooting percentage being 90% in both) and Gisela 5 (70%). Rooted shoots were successfully acclimatized under the mist system in greenhouse.

The viability of ovules was studied in five plum cultivars under laboratory conditions at four constant temperatures: 5ºC, 10°C, 15ºC and 20ºC and under field conditions over two years. During 10 days from the onset of full bloom, ovule viability in cvs CaCanska Rana,CaCanska Najbolja and CaCanska Lepotica was between 80-100 % at the temperatures of 5ºC, 10ºC and 15ºC, in both years. In the same period, ovule viability in cvs Wangenheims Frühzwetsche and PoegaCa was lower, but never below 50%. At the constant temperature of 20ºC, all plum cultivars showed a decline in longevity of ovule viability, which was pronounced in cv. CaCanska Rana. During the 10 days from the onset of full bloom, ovule viability in all five plum cultivars under field conditions showed a high viability, which approximated to the ovule viability of the cultivars at the constant temperatures of 5ºC, 10ºC and 15ºC, in both years. Determination of the longevity of ovule viability in the mentioned plum cultivars is of great importance due to its effect on the effective pollination period and fertilisation success. This paper deals in detail with the interrelations between the temperature effects on ovule viability, pollen tube growth and fertilisation, as well as on fruit setting.

Murashige and Skoog medium (MS) and modified Anderson's Rhododendron medium (mAN) were compared for in vitro shoot multiplication of three highbush blueberries 'Berkeley', 'Bluecrop' and 'Goldtraube'. All media contained 0.5 mg l −1 zeatin applied either alone or combined with 0.1, 1 and 5 mg l −1 IBA. In vitro rooting was induced using mAN medium supplemented with 0.8 mg l −1 IBA and 4 g l −1 activated charcoal. The results obtained showed that mAN medium is more suitable for in vitro multiplication of the selected highbush blueberry cultivars than MS medium. Low concentration of IBA (≤1 mg l −1) added in zeatinsupplemented mAN medium increases shoot multiplication efficiency of highbush blueberries in vitro and can be recommended for large-scale propagation of high-quality plants. MS medium induced partial or full necrosis of stems and leaves, which was more pronounced on media containing zeatin combined with increasing concentration of IBA. Rooting capacity of shoots varied widely among the tested blueberry cultivars. The highest rooting and acclimatization rates were achieved in 'Goldtraube' (82.8% and 91.8% respectively), and the lowest (10% and 66.7% respectively) were in 'Berkeley'.

The incompatibility genetics of sour cherry ( Prunus cerasus), an allotetraploid species thought to be derived from sweet cherry (diploid) and ground cherry (tetraploid), were investigated by test crossing and by analysis of stylar ribonucleases which are known to be the products of incompatibility alleles in sweet cherry. Stylar extracts of 36 accessions of sour cherry were separated electrophoretically and stained for ribonuclease activity. The zymograms of most accessions showed three bands, some two or four. Of the ten bands seen, six co-migrated with bands that in sweet cherry are attributed to the incompatibility alleles S(1), S(3), S(4), S(6, ) S(9) and S(13). 'Cacanski Rubin', 'Erdi Botermo B', 'Koros' and 'Ujfehertoi Furtos', which showed bands apparently corresponding to S(1) and S(4), were test pollinated with the sweet cherry 'Merton Late' ( S(1) S(4)). Monitoring pollen tube growth, and, in one case, fruit set, showed that these crosses were incompatible and that the four sour cherries indeed have the alleles S(1) and S(4). Likewise, test pollination of 'Marasca Piemonte', 'Marasca Savena' and 'Morello, Dutch' with 'Noble' ( S(6) S(13)) showed that these three sour cherries have the alleles S(6) and S(13). S(13) was very frequent in sour cherry cultivars, but is rare in sweet cherry cultivars, whereas with S(3) the situation is reversed. It was suggested that the other four bands are derived from ground cherry and one of these, provisionally attributed to S(B), occurred frequently in a small set of ground cherry accessions surveyed. Analysing some progenies from sour by sweet crosses by S allele-specific PCR and monitoring the success of some sweet by sour crosses were informative. They indicated mostly disomic inheritance, with sweet cherry S alleles belonging to one locus and, presumably, the ground cherry alleles to the other, and helped clarify the genomic arrangement of the alleles and the interactions in heteroallelic pollen.