The Olive Tree and Its Cultivars

Class: Magnoliopsida

Order: Lamiales

Family: Oleaceae

Genus: Olea

Species: europea

Origin

The origin of the olive is lost in the millennia. It is thought to come from Asia Minor, more precisely the area between the Caucasus, the Iranian Plateau and the Syrian and Palestinian coasts, from where over thousands of years it spread across the Mediterranean basin, to the coastal and near-coastal areas of almost the whole Mediterranean.

Discoveries on the seabed off Palestine have shown that its origin dates back as far as 6,000 years, as is also demonstrated by the discovery in the Syro-Palestinian area of remains of cultivated olives similar to today’s wild ones.

Botanical characteristics

The olive (Olea europea) is a plant that lives for centuries. It has evergreen leaves and, in the wild, begins to bear fruit after a long juvenile period, maintaining good production for many years. Its leaves are lanceolate, on average 5 to 8 centimetres long, green on the upper side and silvery grey underneath because of the many hairs that protect them from excessive transpiration; they last on average about 2 years.

The root system is fairly extensive and very shallow, consisting mainly of adventitious roots that spread laterally and close to the surface. In the adult tree the collar area (the point where trunk and root meet) is swollen and broad (it is called the “pedale”, “ceppaia” or “ciocco”) and is characterised by more or less spherical growths from which shoots (suckers) easily develop; if the base of a sucker is buried, it readily puts out roots, giving rise to a “rooted sucker”.

The trunk, grey-green and smooth until about the tenth year, then becomes gnarled, rough, deeply furrowed and twisted, and takes on a dark colour; it is longer or shorter depending on the training system chosen. Trees that are centuries old can reach remarkable size, both in height and in width. The trunk bears the main limbs, which carry the branches; on these grow the shoots, which are the growths that develop during the year.

Shoots that grow on the upper side of branches and limbs and develop rapidly and vigorously are called water sprouts.

Leaves form on the branch from spring to autumn and remain alive until they are two years old. In the axil of each leaf there is a bud, which may give rise to an inflorescence (if it was a flower bud) or to a shoot (if it was a wood bud). Many wood buds can remain dormant and develop even after several years, for example following heavy pruning cuts.

The olive flower is hermaphrodite, that is, it has both the male organs (two stamens) and the female organ (pistil); it is very small (3–5 mm) and its corolla consists of four whitish petals fused together at the base. The pistil is stout and short, with a broad feathery stigma rich in papillae and therefore very well suited to catching pollen.

However, a large proportion of Italian varieties are self-sterile, so olive fertilisation is mainly heterogamous (that is, with plants that have two distinct types of flower): pollination is anemophilous (that is, it takes place by means of the wind), even over considerable distances between trees. A phenomenon typical of the olive is ovary abortion, which occurs to differing degrees in different varieties and, within the same variety, in different proportions from one year to the next. It consists of the failure or insufficient growth of the ovary and is strongly influenced by the tree’s nutritional state, so its incidence can be reduced through good cultivation practice; fewer than 10% of flowers go on to develop fully into fruit.

The flowers are not single but grouped in an inflorescence resembling a small cluster, commonly called a “mignola”. The mignole develop from the flower buds that form in the leaf axils and begin to grow; the olive is then said to be at the “mignolatura” stage. This is followed by flowering proper (the opening of the flowers), which, depending on the year and the latitude, can take place between the end of April and June.

After 6 months the olives formed from the flowers (about 5% of the flowers) will ripen.

The fruits weigh from 2 to 20 grams and change colour (“invaiatura”, or veraison) from green to yellow to purple to violet-black. They ripen from October onwards, and at the same time as the colour change, ripening or “inoliazione” (oil accumulation) takes place, during which the water, sugar and acid content of the pulp decreases and the oil content increases.

Fruiting, that is the production of olives, depends on factors linked to the plant’s annual development, both nutritional and agronomic (irrigation, pruning, harvesting); a heavier fruit load comes with less shoot growth and therefore less fruiting the following year.

“On” year: good production, reduced vegetative activity; “off” year: low production, high vegetative activity.

There are hundreds of olive varieties (cultivars) – for oil, for the table and dual-purpose – which differ in shape and size and are characterised by a different stone-to-pulp ratio and therefore an average oil content ranging from 18 to 27%. Their productivity depends on a great many climatic and cultivation factors that determine the two-year cycle of full production.

Such a large number of cultivars is due to changes in the genotype (as a result of bud mutations fixed through vegetative propagation, or through spontaneous crossing followed by seed dispersal) or to fluctuation in varietal traits as a result of environmental conditions.

The production specification for the protected designation of origin “PDO Molise”, recognised in the Official Gazette of the Italian Republic no. 137 of 14/06/2000, lists for the province of Isernia, together with the Leccino variety, the Aurina, used for at least 80%, jointly or separately, with the remaining 20% made up of other native varieties.

The planting distances, training forms and pruning systems of these olive groves must be those best able to enhance the qualitative characteristics of the oils

Several varieties are found within the Venafro Olive Park. The catalogued national varieties are omitted here, while for information purposes we set out the bio-morphological and phenological characteristics of the lesser-known native ones, namely: