Promising directions in apple breeding
Long-term data are given on priority directions in apple breeding: for an increased content of biologically active substances in fruit and for scab resistance. The high effectiveness of apple breeding at the polyploid level is shown.
Polyploidy affects the development of Venturia inaequalis in scab-resistant and -susceptible apple cultivars
Abstract Apple (Malus × domestica Borkh.) production is significantly affected by apple scab disease caused by the fungus Venturia inaequalis. Currently, management of the disease is largely based on fungicide applications and less on the inherent resistance in apple cultivars carrying resistance (Rvi) genes. Moreover, the durability of both approaches is questionable, since new virulent strains with resistance to fungicides and/or Rvi genes can develop. Hence, a combination of complementary management strategies is needed to tackle apple scab. To broaden the management options, a viable approach might be the breeding for polyploid cultivars and their implementation in commercial orchards. Apple germplasm is substantially characterized by polyploidy, which throughout the evolution of angiosperms often led to improved adaptation to adverse climatic conditions and abiotic stresses. However, the role of polyploidy in conferring resistance to biotic challenges is less clear. Here, we show that autopolyploidy in two apple cultivars, i.e. the susceptible ‘Gala’, and the resistant ‘Makali’ which carries the Rvi6 scab resistance gene, can reduce severity of apple scab symptoms upon inoculation with two different V. inaequalis isolates. Leaves of tetraploid plants show reduced sporulation symptoms in comparison with their diploid counterparts upon infection with both pathogenic strains, attributed to a reduced presence of V. inaequalis. These results suggest that polyploidy enhances resistance of apple cultivars against different V. inaequalis isolates. However, the degree of the enhanced resistance depends on a plant-pathogen-specific interaction. The knowledge provided here offers a relevant framework for improving our understanding of polyploidy-enhanced resistance to biotic stress in plants and may set the stage for implementing polyploidy breeding for further genetic improvement of apple.
Redistribution of rare-earth elements during diagenesis of carbonate rocks from the Mid-Proterozoic Newland Formation, Montana, U.S.A.
Abstract REE data for carbonate rocks from the Mid-Proterozoic Newland Formation, Belt Supergroup, show variable degrees of relative REE enrichment when normalized to a composite shale of the Newland Formation. Most conspicuous are relative enrichments in LREE's and positive Eu anomalies. Possible coprecipitation of REE's in carbonates from seawater is much too small to account for the REE enrichment, thus only diagenetic REE enrichment has to be considered. By far the strongest LREE enrichment is observed in carbonates with interbedded shales. During diagenesis REE apparently moved from the shale partings to the adjacent limestone beds. Massive limestone units have considerably smaller REE enrichments (except in proximity to shales), suggesting that REE addition from formation waters is less efficient for supplying REE's than is local redistribution between shale and limestone beds. Early precipitation of diagenetic silica in pore spaces reduces REE enrichment in limestone beds by reducing their permeability. Dolostones are cemented by pervasive early-diagenetic silica and lack significant REE enrichment except for Eu, probably because silica cement prohibited access of REE-bearing pore waters. Positive Eu anomalies indicate reduction of Eu to the divalent state during diagenesis and relatively large mobility of divalent Eu.