The Variability of Juvenile Period, Fruits Size and Response to Diseases Attack on F1 Interspecific Apple Hybrids and the Efficiency of Selection

Interspecific hybridizations represent one of the apple breeding methods by which a wide variability can be achieved, useful for creating new cultivars. The study of 2190 interspecific hybrids, obtained from 25 combinations among crab apple species (Malus coronaria, M. floribunda, M. niedzwetzkyana, M. zumi, M. prunifolia) and different apple cultivars, points out a large variability of the F1 seedlings for several traits, with significant importance in apple breeding programs. The first year of fructification, as mean per hybrid combination, varied from 6 (M. zumi x ‘Jonathan’) to 9.3 years; the average hybrid’s age for fructification was 7.4 years. The size of fruits among families varied from 1.5 (‘Starkrimson’ x M. prunifolia) to 4.0 (‘Reinette Baumann’ x M. zumi), the mean being settled at 2.8 (therefore below mark 3, meaning ‘small fruits’). The lowest infection rate both for apple scab and powdery mildew attack was noticed at hybrids from M. coronaria x ‘Reinette Baumann’. On the whole, the hybrids with genitors of ‘species x cultivars’ type have had an early fruiting and a better resistance to scab and powdery mildew, compared to the ones from ‘cultivars x species’ combinations. The large variability of the studied traits gave the possibility to identify offsprings with desirable characteristics on nine hybrid combinations. Among these, 53 elite plants were selected, with a strength of selection of 2.42%, therefore a relative low value, correlated with the peculiarities of the interspecific population and the selection criteria for dessert apple.