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Filderstadt, Germany

Lichtenegger L.,Ludwig Maximilians University of Munich | Treutter D.,Ludwig Maximilians University of Munich | Neumuller M.,Ludwig Maximilians University of Munich | Hartmann W.,Erikaweg 5
Acta Horticulturae | Year: 2012

Until now there have been many investigations according the inheritance of the hypersensitivity resistance against the Plum pox virus (PPV) in European plum (Prunus domestica L.). For establishing an effective breeding program for PPV resistance it is important to know more about the inheritance and the genetic determination of the hypersensitivity resistance. There have been investigations concerning the inheritance of the hypersensitive resistance by screening seedlings of selected crossing combinations. These seedlings resulted from crossings between two hypersensitive parents, between hypersensitive and sensitive parents and between two sensitive parents. Moreover quantitatively resistant genotypes were crossed with hypersensitive resistant genotypes. One can show that the inheritance depends on the degree of hypersensitivity resistance in the parent genotypes. The higher the degree of hypersensitivity the higher is the amount of hypersensitive progenies. Furthermore it strongly depends on the selection of the crossing partners. In combinations with two hypersensitive partners, the percentage of hypersensitive seedlings is higher, than in combinations of hypersensitive genotypes with sensitive ones. The amount of hypersensitive progenies in crossing combination of hypersensitive genotypes with a quantitative resistant one is lower than in combination of hypersensitive genotypes with a sensitive one. In order to clarify the origin of the hypersensitivity resistance, progenies of crossing combinations from 'Ortenauer' × 'Stanley', 'Ortenauer' × 'Ortenauer' and 'Stanley' × 'Stanley' have been tested. This refers to 'Jojo', the first completely hypersensitive cultivar, which is a descendant of a crossing between 'Ortenauer' and 'Stanley'. The results show that the donor of the hypersensitivity resistance is the cultivar 'Ortenauer'.

Hartmann W.,Erikaweg 5 | Neumuller M.,TU Munich
Acta Horticulturae | Year: 2013

Plum growing in Sharka infested regions is only successful with Sharka resistant cultivars. The cultivar 'Jojo', up to now the only cultivar which is absolutely Sharka resistant in the field, was introduced by the University of Hohenheim in 1999. The resistance is based on a hypersensitive response to the Sharka virus (Plum pox virus, PPV). Since its release a number of new hypersensitive clones were bred within the Hohenheim breeding program that have different ripening times, better quality and higher fruit weights. These include interesting clones with early, midseason and late ripening times. A particular breeding aim is the combination of resistance and high fruit quality. Crosses of hypersensitive genotypes with the cultivars 'Hanita', 'Felsina' and 'Fellenberg' gave promising seedlings. There are some clones that combine a high degree of hypersensitivity resistance with excellent fruit quality. Clone Nr. 7346 will soon be introduced as new cultivar. Crosses of 'Jojo' with 'Haganta' resulted in two PPV resistant clones with fruits larger than 50 g. Some clones originating from the cross 'Jojo' × 'Hauszwetschge' vary in ripening times and are also very interesting. Some of the very promising hypersensitive hybrids are very similar to 'Common prune' in shape, colour, size and taste. These promising clones cover more than six weeks of ripening time. Their fruits are resistant to fruit flesh damage caused by excessive heat as fruit mature which is a current problem with fruits of 'Common prune'. These clones will be introduced as new PPV resistant cultivars. They will allow growers to sell fruits of 'Hauszwetschge' (i.e. 'Common prune') and very similar fruits from the middle of August until the beginning of October.

Neumuller M.,TU Munich | Muhlberger L.,TU Munich | Siegler H.,Bayerische Landesanstalt fur Weinbau und Gartenbau | Hartmann W.,Erikaweg 5 | Treutter D.,TU Munich
Acta Horticulturae | Year: 2013

A breeding program with the aim of obtaining Plum pox virus (PPV) resistant rootstocks for stone fruit cultivars was established at Technische Universität München. Genetic crosses between European plum (P. domestica) genotypes with hypersensitivity resistance to PPV were used as one parent and either P. spinosa or P. cerasifera as the other parent resulting in either 'Dospina' or 'Docera' rootstock candidates, respectively. The seedlings were screened for hypersensitivity resistance. The PPV resistant clones were screened for easy vegetative propagation by green cuttings, hardwood cuttings and in vitro propagation. The selected seedlings were retested extensively for PPV resistance with several European plum cultivars differing in their susceptibility to PPV. PPV infected budsticks of these cultivars were grafted onto the rootstock candidates either in spring or in summer. In many cases, the infected buds were rejected by the rootstock before bud break. Otherwise the young shoot which started to grow from the infected bud or budwood was rejected by the rootstock within several weeks after bud break. Due to this selfeliminating effect of PPV infected buds or scions grafted onto the newly developed PPV resistant rootstocks, no PPV infected tree developed to a marketable size. First results obtained from pomological tests indicate that trees grafted onto 'Docera 6' show similar vegetative and generative properties as those grafted onto 'St. Julien A' rootstock. National and international tests for the pomological evaluation of the rootstock are underway. In a first step, the new hypersensitive rootstocks will be used for newly bred hypersensitive plum cultivars. In this way, neither the rootstock nor the scion cultivar can get infected with PPV under natural inoculation conditions. This gives the highest level of security to damages caused by PPV which is available in stone fruits species at the moment. In a second step, their use for PPV sensitive European plum cultivars as well as for apricot, Japanese plum and peach is under evaluation.

Hartmann W.,Erikaweg 5 | Lichtenegger L.,TU Munich | Neumuller M.,TU Munich
Acta Horticulturae | Year: 2012

In a breeding cycle from the years 1998 to 2002, we crossed 'Jojo' and his sibling 'Ort. x Stan. 34' with 25 different late ripening cultivars. We received more than 2500 seedlings. From this material were selected 56 clones for a second selection stage carried out in different regions. 43 of these clones showed strong hypersensitivity resistance to the Sharka virus. The clones are ripening between the end of July and the beginning of October. There is a variation in fruit weight between 18 and 88 g. Results of the second selection stages are discussed. In a new breeding cycle from 2002 to 2005 crossings were made with the following breeding aims: Early or late ripening, large fruit size, hypersensitivity resistance to Sharka disease; quality, fruit size and hypersensitivity. From crossings with 11 different cultivars, we obtained 467 seedlings. First fruits have been harvested in 2006. Interesting clones were tested for hypersensitivity resistance. First results concerning the pomological value are presented.

Neumuller M.,TU Munich | Ruhmann S.,TU Munich | Treutter D.,TU Munich | Hartmann W.,Erikaweg 5
Acta Horticulturae | Year: 2012

Fruit size, flesh firmness, color of the fruit skin and the flesh, adherence of the fruit flesh to the stone, caverns within the fruit flesh, content of sugars, organic acids and aroma components are important quality traits in European plum. In order to improve the fruit quality of European plum the main influencing factors on fruit quality have to be known. Fruits of different European plum cultivars and breeding clones originating from the Hohenheim and Weihenstephan plum breeding program were harvested and analyzed concerning 20 different fruit characters amongst them the soluble solid content, the organic acid content, fruit mass, fruit length and width. The influence of the locations, the harvesting time and the crop load on fruit quality was compared. Both picking time, crop load and the genetic determination were shown to be important influencing factors on fruit quality. In many cultivars, fruits harvested from PPV infected trees were of lower fruit quality than fruits grown on healthy trees. Thus, breeding can be regarded to hold the key position in enhancing fruit quality in Prunus domestica. However, crop load and harvesting time have to be optimized as well in order to exhaust the full genetic potential of a respective genotype.

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