Evaluation of morphological and chemical characteristics and micropropagation of traditionally grown domesticated apple varieties in Croatia

Traditionally grown domesticated apple varieties are known for their adaptability to different climates and a wide range of soil types, and some for resistance to the main diseases. Their evaluation and preservation are very important, not only for restoration of traditional orchards, but also as a source of genetic material for breeding new varieties. Micropropagation of the most valuable varieties could be a way to propagate plants for restoration of traditional orchards, or as a prerequisite for ex situ long-term conservation through cryopreservation. Fruit samples were taken from trees 50 or more years old, of 13 traditionally grown domesticated apple varieties in Bjelovar Bilogora County in Croatia. Morphological traits of the fruits were evaluated during 3 years, and chemical characteristics (soluble solids, reducing sugars, acids and total phenol content) were evaluated during one vegetation year. Tissue culture was established from shoot apices approximately 1 mm in size isolated from buds of 1-year-old scion woods. Axillary branching was induced from two types of explants on MS medium with the addition of 2% glucose, 1% sucrose, 0.1 g L−1 myo-inositol, 0.8% agar, 0.2 mg L−1 gibberelic acid (GA3), 0.1 mg L−1 indole-3-butyric acid (IBA) and 1.5 mg L−1 6-benzylaminopurine (BAP) in proliferation medium 1 (PM1) or 2 mg L−1 zeatin (ZEA) in proliferation medium 2 (PM2). The morphological characteristics of the traditionally grown domesticated apple varieties mentioned were not different from their standard values. Average fruit weight (AFW), average fruit height (AFH) and average fruit diameter (AFD) were less than standard values, which can be explained by the age of the fruit trees. Principal component analysis of these traditionally grown domesticated apple varieties showed that fruit traits very important in today’s breeding for new cultivars, like fruit weight, shape, skin color and flesh taste, stand out in explaining the variability. Despite the age of the fruit trees, the fruits still have surprisingly positive chemical characteristics, especially Canadian Reinette for which the highest concentration of total phenols was found. Of the five traditionally grown domesticated apple varieties used, tissue culture was successfully established for Jonathan and Canadian Reinette varieties. Higher multiplication efficiency was obtained for the Jonathan variety. Medium supplemented with 1.5 mg L−1 BAP produced a significantly higher number of shoots/explant in comparison with those supplemented with ZEA. Morphological features of shoots produced on medium supplemented with ZEA, however, were better. Both explant types, shoots placed in the medium vertically or two-nodal stem segments placed in the medium horizontally, gave similar results for axillary branching.