Cercospora leaf spot, caused by the fungus Cercospora beticola, is a major fungal sugar beet disease worldwide and the cause of significant yield losses. The disease is most successfully countered by the introduction of genetic tolerance into elite sugar beet hybrids. To this end, breeding programmes require high quality biological assays allowing discrimination of minor differences between plants within a segregating population. This study describes the successful implementation of image analysis software in the bioassays for quantification of necrotic lesions at different stages of C. beticola infection, allowing selection on minor phenotypic differences during the sugar beet breeding process for C. beticola resistance. In addition, a real-time PCR assay was developed for the quantification of C. beticola pathogen biomass in infected beet canopy. The use of both techniques, even in an early stage of infection, fine-tunes current bioassays, allowing more accurate and efficient selection of resistant breeding material.

Both ploidy variants were typified as highly sensitive to drought-induced cavitation, with no significant difference in their overall drought vulnerability. But, when water deficit is short and moderate, Gala-4x may delay a drought-induced decrease in performance by trading hydraulic safety for increased release of capacitively stored water from living tissue.

The authors acknowledge VLAIO (Flanders Innovation & Entrepreneurship) for their financial support (project number 090940) and Better3Fruit for offering Malus × domestica genotypes. Barbara De Coninck, for providing corrections and improving the language of the manuscript, Karmen Pogacar and Silvia Bonilla for their technical assistance and the greenhouse staff of KU Leuven for their advice and assistance are also greatly appreciated.

Hias N., Leus L., Davey M.W., Vanderzande S., Van Huylenbroeck J., Keulemans J. (2017): Effect of polyploidization on morphology in two apple (Malus × domestica) genotypes. Hort. Sci. (Prague), 44: 55-63.Because polyploidy often results in enhancement of desirable properties, artificial genome doubling is commonly used in agri-and horticultural crop breeding programs. In this study genome doubling was induced in two apple genotypes. The effect on vegetative morphological and physiological traits of the plants was then comprehensively determined by comparing the obtained tetraploid apple plants with their diploid counterparts. Out of 17 different physio-and morphological characteristics, 15 were significantly affected in one or both genotypes. The response of these 15 characteristics also appeared to have been caused by two effects; 10 of the 15 characteristics exhibited a common response to ploidy change over both genotypes while five traits showed a genotype-specific response to polyploidization. Tetraploid leaves also exhibited a darker leaf colour, which could be correlated to a higher pigment concentration. Furthermore, the results also show a decreased elongation rate and leaf size in tetraploids, which is suggested to be due to the observed lower cell density in the polyploid apple plants.

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