Freshly consumed apples can cause allergic reactions because of the presence of four classes of allergens, namely, Mal d 1, Mal d 2, Mal d 3, and Mal d 4, and their cross-reactivity with sensitizing allergens of other species. Knowledge of environmental and endogenous factors affecting the allergenic potential of apples would provide important information to apple breeders, growers, and consumers for the selection of hypoallergenic genotypes, the adoption of agronomical practices decreasing the allergenic potential, and the consumption of fruits with reduced amount of allergens. In the present research, expression studies were performed by means of real-time PCR for all the known allergen-encoding genes in apple. Fruit samples were collected from 15 apple varieties and from fruits of three different trials, set up to assess the effect of shadowing, elevation, storage, and water stress on the expression of allergen genes. Principal components analysis (PCA) was performed for the classification of varieties according to gene expression values, pointing out that the cultivars Fuji and Brina were two good hypoallergenic candidates. Shadowing, elevation, and storage significantly affected the transcription of the allergen-encoding genes, whereas water stress slightly influenced the expression of only two genes, in spite of the dramatic effect on both fruit size and vegetative growth of the trees. In particular, shadowing may represent an important cultural practice aimed at reducing apple cortex allergenicity. Moreover, elevation and storage may be combined to reduce the allergenic potential of apple fruits. The possible implications of the results for breeders, growers, and consumers are discussed critically.

While at present the strategies for thinning the main apple cultivars are based on carbaryl, from 2008 onwards growers will have to try to achieve adequate crop load without this well known compound. The tank-mix NAA + benzyladenine proved to be an option for thinning difficult cultivars like 'Fuji' by using active ingredients that will still be available after 2008. Intensive but selective thinning occurred using metamitron, an a. i. currently registered as herbicide that has been recently proposed by the EUFRIN Thinning Group as a high-potential molecule for crop load control.

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The adoption of high-density plantings (HDP) in apple orchards started with the introduction of dwarfing rootstocks from East Malling’s (UK) breeding program. A range of spindle-derived training systems have been developed to improve light interception/distribution with a variation in leader numbers. Many of these training systems cannot guarantee early, consistent, and uniform illumination of the entire canopy. For this reason, planar 2-D canopies have been developed with varying numbers of primary axes with numerous second-order shoots. In this trial, carried out at the nursery level, three sites were selected: one in New Zealand (Hawke’s Bay Research Centre) and two in Italy (Bologna and Trento). Trees were produced with a single-, bi-, and tri-axis system utilizing three rootstocks (‘M27’, ‘M9’, ‘MM106’), characterized by an increasing level of vigor. The cultivation site played an important role in modulating early tree performance. Multi-leader trees reduced average shoot length in the Italian sites in the first year after grafting. The number of shoots and total growth developed on multi-leader trees was higher than single-axis trees. This may benefit growers that seek to use canopy architecture manipulation to fill space and control vigor when establishing HDP orchards.