Breeding aims

3.2.1. Breeding aims and cultivar use of sweet cherry

Sweet cherry fruits are consumed mostly fresh, therefore the features connected to fruit appearance are important from the breeding point of view. Fruit size, taste, flesh firmness are quantitative features, which means that a high deviation can be observed in progenies concerning these features.

The most obvious and most important characteristic is fruit size, which ideally can reach a diameter of 28-30 mm. There are differences between cultivars in their potential fruit size (e.g. ‗Müncheberger Frühe‘ has small fruits, while ‗Schneiders Späte Knorpelkirsche‘ has large fruits), but cultivation technology (nutrient and water supply, pruning, thinning) can highly increase or decrease the genetically determined fruit size. Some cultivars have a tendency to oversetting, so fruits can become smaller.

Cultivars ‗Celeste‘ and ‗Sunburst‘ inherit the large fruit size well.

Regarding skin colour preferences, there can be differences between continents and countries. While in Europe red-skinned sweet cherries are popular, in the USA blushed types are also preferred. In Asia, cultivars with reddish yellow, pinkish orange skin are preferred. Each breeding program keeps the local needs in mind.

Sweet cherries with crunchy flesh are preferred instead of those having soft flesh. Where there is more precipitation during ripening, cultivars with firm flesh can easily crack, therefore soft-fleshed varieties

(e.g. Merton series) are cultivated in such habitats (e.g. England). Early-ripening varieties have generally a softer flesh.

In the USA, one of the main aspects of breeding is firm flesh, because it guarantees good transportability. Fruits often have a long journey on ships until they arrive to another American state or country. Another breeding aim is resistance to fruit cracking. Cracking is often tried to be avoided by technology. Cultivation technology is intensive and stands on a high level in America. Late-ripening cultivars (e.g. ‗Sweetheart‘, ‗Skeena‘) are popular, and sweet cherries harvested in August on high altitude areas can be sold at a higher price.

Sweet cherry is the first fresh fruit of the year and consumers are willing to pay more for it. Therefore early ripening time of cultivars is an important breeding aim. The earliest market varieties at present are the French ‗Early Bigi‘ and the Hungarian ‗Rita‘. Breeding of early-ripening sweet cherries is difficult, because soft flesh, poor taste and small fruit size is frequent among variants originating from the crosses, and fruits may not ripen at the same time on the tree. Early-ripening varieties are bred and cultivated mainly in areas with warmer climate, where the harvest of early varieties can take place as early as possible. Italy (mainly the University of Bologna) stands out in breeding early cultivars.

The sweet cherry season can be prolonged, as well as in cool areas, the harvest period can be extended by cultivating late ripening varieties. Late cultivars have less disadvantageous characteristics than early ones. Well-known late-ripening cultivars are ‗Regina‘ (Germany) and ‗Staccato‘ from the Canadian breeding program, as well as the Hungarian ‗Alex‘.

Self-fertile sweet cherry cultivars increase the yield safety, therefore self-fertility is an important breeding aim. Since the first self-fertile cultivar appeared, all breeding centres have produced such cultivars.

Their disadvantage is that they are susceptible to oversetting, so fruits become small, therefore these trees require thinning. Among Hungarian cultivars, the male names indicate self-fertility. In Canada, the breeding of self-fertile cultivars is carried out for long at the Summerland Research Station. A number of large-fruited, self-fertile, late ripening cultivars were bred there (‗Skeena‘, ‗Staccato‘). Their newest target is to breed blushed sweet cherries.

If there is precipitation during ripening, the water can cause fruit cracking. Precipitation can occur during ripening in most countries, therefore a lower susceptibility to cracking is an important breeding aim.

According to the experiences of breeders, cultivars ‗Regina‘ and ‗Kordia‘ inherit well this lower susceptibility to cracking. We do not have enough knowledge about the mechanism of crack resistance yet, so breeding in this respect is difficult. Less susceptible cultivars (e.g. ‗Regina‘) are used in breeding programs.

In California, the occurrence of sweet cherry double fruits is a problem, caused possibly by the high summer temperatures during bud differentiation.

Abiotic stress tolerance can vary by growing sites. In areas with cold winter (Norway, Russia) the winter hardiness as well as winter and spring frost resistance of cultivar are important. The latter can be avoided by cultivating late-flowering varieties. In subtropic areas, cultivars with low chilling requirement have significance (e.g. ‗Royal Lee‘).

Distribution of sweet cherries without stem is allowed in the European Union, which makes machine harvest possible even for fresh market sale. Therefore a new breeding aim is to create cultivars with dry stem scar. Such cultivar is for example ‗Linda‘.

Pathogens of sweet cherry can vary between geographic areas. The most frequent pathogens are Cytospora canker (Cytospora cincta), leaf spot (Blumeriella jaapii) and brown rot (Monilinia fructigena).

Among bacteria, Pseudomonas species are important to mention. In areas with arid climate, powdery mildew (Podosphaera oxyacanthae) can occur as well.

As sweet cherry is mostly hand-harvested, the utilization of less vigorous rootstocks is important. The most popular of them are GiSela and Weiroot rootstock series. In Italy, there is an endeavour to breed spur type scion cultivars (e.g. ‗Lambert compact‘).

Sweet cherries are cultivated and bred not only for their fruits but for their wood as well in more Western European countries (e.g. England, Belgium, France).

Sweet cherry cultivar use of different countries shows a high variation. A favourite variety of the Americans, originating from the 1800‘s, is ‗Bing‘: a sweet cherry ripening in the medium period, with claret skin, good to transport. It is susceptible to cracking, self-sterile, growers try to replace it with new cultivars. The other popular red-skin cultivar is ‗Lapins‘. Also preferred varieties are the blushed sweet cherries, like ‗Rainier‘. In California, Zaiger's Genetics carries out cherry breeding, but their cultivars have low chilling need, so not suitable for areas with cold winter. Its new cultivars are the members of

―royal‖ series (‗Royal Edie‘, ‗Royal Helen‘, ‗Royal Hazel‘, ‗Royal Bailey‘).

In Italy, early cultivars have a great significance (‗Early Bigi‘, ‗Burlat‘), while other popular cultivars in the region, among others are ‗Celeste‘, ‗Grace Star‘, ‗Lapins‘. Breeding targets involve bright, red-skin, self-fertile, large-fruited, crunchy varieties. Ripening time of the new ―star‖ cultivar series (‗Sweet Early‘,

‗Early Star‘, ‗Grace Star‘, ‗Blaze Star‘, ‗Big Star‘, ‗Black Star‘, ‗LaLa Star‘) cover the whole harvest period.

Turkey is a potential competitor of the USA on the sweet cherry world market. Extensive sweet cherry orchards can be found throughout the country. In Izmir, by the Aegean Sea, sweet cherry ripens from early May, while people harvest in August in the mountains of Anatolia. In most cases they cultivate local varieties, like ‗Ziraat‘. They grow often for juice or dried fruit production. Trees are not pruned, so they grow high, there is no irrigation, and there is a lack of expertise.

Spanish sweet cherry cultivation is significant, there are orchards in the lower Jerte valley, in Aragonia, in Granada and in the Valencian mountains. Sweet cherry season lasts from end April until July, so they are now market leaders regarding early cultivars. They grow cultivars such as ‗Burlat‘, ‗Ramon Oliva‘,

‗Van‘, ‗Sunburst‘, ‗Sweetheart‘ and some local varieties.

French breeding is carried out in Bordeaux from the 1970‘s. Their new cultivars are ‗Early Bigi‘, ‗Folfer‘

(early cultivars) and ‗Fertard‘.

In Japan, breeding is pursued for about 50 years, they breed sweet cherries with light-coloured or blushed skin. Their novelty is ‗Benitemari‘.

Lately, sweet cherry breeding is carried out in other countries of Asia, of which we do not know much.

3.2.2. Breeding aims and cultivar use of sour cherry

There are two types of sour cherry cultivars. The fruit flesh of amarelle sour cherries are light-coloured, the juice is colourless (e.g. ‗Montmorency‘), also the skin is a bit lighter. Cultivars of morello type have dark flesh and juice, which is often dyed.

Sour cherry is consumed mostly after processing in the world, except in countries of Eastern-Central Europe, where sour cherry is often eaten fresh.

Fruit size is important in case of fresh consumption sour cherries, a diameter of 24-26 mm, bright skin and a balanced taste (acid-sugar ratio) is desirable. Pándy sour cherry (syn.: Köröser Weichsel) is characterized by an advantageous fruit appearance and taste, this is the basic parent cultivar of European breeding programs. Fruits have to be harvested with the stem, on which a small or large stipule can be found depending on the cultivar. The aim is to breed cultivars whose stem is without stipule and to facilitate harvest, a long stem is required.

The earliness of cultivars increase their market value, as for sweet cherries, therefore it is a desirable feature. Here as well, earliness is often accompanied by small fruit size, and self-sterility.

Sour cherries intended for processing are harvested by machine. Sour cherries can be processed for compote, jam, frozen fruits, juice, dried fruit, brandy, chocolate cherry liqueur praline. For confectionary purposes, cultivars with light-coloured skin and colourless juice (e.g. ‗Montmorency‘) can be taken into consideration. Seed content of fruits should be less than 8%. For juice and food dye production cultivars with are suitable, which have a high acid and pigment content, fruit size is indifferent in this respect (e.g.

‗Cigánymeggy‘).

In case of machine harvest, the suitability of cultivars for shaking is important (the fruit should separate from the stem easily and dry). To facilitate machine harvest, in the Canadian breeding program new cultivars with a special shrub habit are bred, which have a good fruitfulness and dwarf habit without a rootstock decreasing its vigour.

For canning varieties with firmer flesh and a medium fruit size are suitable.

Because of the health protecting effect of sour cherry, the aim is breeding cultivars with a high antioxidant content as functional food. This is the target of the sour cherry breeding program in the USA (Michigan). Hungarian sour cherry cultivars had a career in the USA because of their outstanding nutritional values: the University of Michigan gave trade-mark protection to cultivars ‗Újfehértói fürtös‘

and ‗Érdi bőtermő‘ under the names ‗Balaton‘ and ‗Danube‘, these varieties are widely planted in the USA.

One of the versatile utilization possibilities of sour cherry is the production of chocolate cherry liqueur pralines, which is unique product of Hungary. Varieties with fruits around 14 mm are suitable for this purpose (e.g. ‗Oblacinska‘). An even smaller size is suitable for ice cream production.

In order to increase yield safety and fruitfulness, breeders make efforts to breed self-fertile cultivars. A significant part of sour cherry varieties in cultivation are self-fertile.

Winter and spring frosts can cause yield losses. According to examinations, cultivar ‗Oblacinska‘ has a good frost tolerance. Frost and cold tolerance are the targets of Russian and Canadian breeding. A significant sour cherry quantity is produced in Russia, mainly local varieties with P. cerasus x P.

fruticosa origin.

An important aim of resistance breeding is to create cultivars which are resistant to Blumeriella leaf spot and Monilinia brown rot. Cultivar ‗Csengődi‘, selected in Hungary, is resistant to the above mentioned diseases, therefore it is an important parent variety of Hungarian sour cherry resistance breeding. A number of foreign breeding centres have set the target to breed resistant cultivars. In Germany (Dresden), the aim is to achieve resistance against Monilia canker and Blumeriella leaf spot, the

―gemstone variety series‖ originates in this program (‗Jade‘, ‗Achat‘, ‗Korund‘, ‗Karneol‘, etc.). In Serbia, a highlighted aspect is resistance against pests and pathogens.

In America, cultivar ‗Montmorency‘ with light red skin can be found in many sour cherry orchards. In Western Europe, ‗Schattenmorelle‘ is a popular variety, which can be marketed fresh or processed as well.

Poland has significant sour cherry cultivation. They produce ‗Schattenmorelle‘, and in addition to it, their own bred varieties are also cultivated, such as ‗Sabina‘, ‗Lucyna‘, ‗Wanda‘, ‗Koral‘, ‗Agat‘, ‗Diament‘,

‗Dradem‘ and ‗Ametyst‘.

In Eastern Central Europe, different types of ‗Pándy‘ (syn.: Köröser Weichsel) sour cherry are well-known, this is an important parent variety of cross-breeding because of its good fruit characteristics. In Serbia, main cultivated varieties are ‗Oblacinska‘ and ‗Cigánymeggy‘, which are grown for freezing, juice production or fresh consumption. Breeding is carried out in the Fruit Research Institute in Ĉaĉak.

‗Pándy‘ sour cherry is frequently used in crosses as a partner. Their known cultivars are ‗Ĉaĉanski rubin‘

and ‗Šumadinka‘.

Hungarian sweet and sour cherry breeding have long tradition. Hungarian cultivars are demanded in the world‘s nurseries, a lot of them have European patent.

3.3. Main cultivars in production