The consumer chooses with his eyes the fruits that he will buy. For apples, the bicolored one’s are especially appreciated. But some particularly strict norms concerning the blushed surface proportion as well as the coloration intensity have been edicted for trade efficiency. The consumer's primary choice must be encouraged. Indeed, the intensity of the red coloration of apples is also bound directly to the development of flavonoïds, natural molecules credited of an important anti-oxydizing activity as well as of another health virtue list that enlarges with the progression of medical studies.[image] However, in the orchard, the coloration development varies from fruit to fruit. This development certainly depends in a first time of the variety (genetic factor), but also of production factors (age and fruit load of trees, nutrition and exposure of the fruit,…) and environnemental features such as the sunshine intensity, the relative air humidity, the night temperature,… In addition to continuous technical improvements, fruit-growers are therefore already looking for new varieties, or better for mutants of known varieties, presenting a meaningful improvement of the produced fruits proportion that answers to norms required by trade. Such mutations are naturally observed in orchards; their occurrence as well as their detection are uncertain and generate however long and repetitive selection works. On the other hand, the in vitro culture techniques, and more especially those aiming to somaclonal variation, offer the possibility to generate, in a limited time, numerous variants of which some features are modified, notably at the fruit level.[image] Au verger, le développement de la coloration dépend principalement de la variété (facteur génétique) mais il varie aussi de fruit à fruit en fonction de certains facteurs de production (âge et charge en fruits des arbres, nutrition et exposition du fruit,…) et des caractéristiques environnementales (ensoleillement, humidité relative, température nocturne,…) Outre l’amélioration continue des techniques culturales, les arboriculteurs recherchent de variétés nouvelles, ou mieux des mutants de variétés déjà connues, présentant une amélioration significative de la proportion des fruits produits qui répondent aux normes exigées par le commerce. De telles mutations s’observent naturellement dans les vergers; leur occurrence ainsi que leur détection aléatoires rendent cependant les travaux de sélection longs et répétitifs. Par contre, les techniques de culture in vitro, et plus particulièrement celles visant la variation somaclonale, offrent la possibilité d’engendrer, en un temps limité et en grand nombre, des variants dont certaines caractéristiques sont modifiées, notamment au niveau des fruits.
Objectives
The initial objective of this project is to analyze and to evaluate the significance, the stability and the recurrence of feature modifications observed on the somaclonal variants in orchard conditions. Besides the observation of the vegetative development of trees, the measurable fruit features deal with the fruit coloration (intensity, precocity and homogeneity of development of the surface color, streaked or plain character, presence of chimeras, green intensity of the shade side), on the tree load, the shape and the mean weight of fruits, as well as on the physical and chemical properties of the fruit (firmness, sugar and starch contents). The recurrence of observations is observed on more numerous duplications (obtained by grafting) for clones presenting particularly some interesting features.
Expected results
The stability and the recurrence of feature modifications have to be observed at least one year more. These trees demonstrate that the somaclonal variation induced in vitro from leaf tissues is efficient to create a great diversity that would be evaluated in a short selection time (5 to 6 years). By the same way, variants of the Pinova variety are in preparation. A first wave of 80 variants has been grafted on M9 and has been planted during the winter 2005-2006.
Results obtained
In the laboratory, adventitious buds of a red mutant of ' Jonagold' have been cloned from 3 successive subcultures of regenerating leaves. More than 200 variants, issued from 3 generations, reached the orchard where trees looked similar growing to the original variety since 1995. The rate of success including micrografting on P22 rootstock and transfer in orchard reached ±90%. First fruits were harvested from several clones in 1998. From 1999 to 2004, characteristics of coloration but also variations in sugar content, starch stage and fruit firmness have been measured on each of the 220 variants. Among these, some are presenting a serious precocity of the fruit coloration (appearing more than 2 weeks before the normal period of maturity of the original cultivar), a red coloration, plain or greatly streaky at maturity, concerning almost 100% of the surface of every fruit. Other modifications could also be noted such as a more elongated shape or a greater firmness of the fruit. [image] 17 clones presenting particular interesting characteristics have been regrafted and replanted in several copies to analyse the grafting recurrence and the stability of these variations on the sites of Gembloux and Merdorp. The retained variants notably for the precocity of the fruit coloration (appearing more than 2 weeks before the normal period of maturity of the original cultivar) confirmed this characteristic; their coloration appears strongly dark red streaky at maturity and concerns almost 100% of the surface of every fruit. Elongated shape, plain blush color (not streaked) and firmness characters of the fruit maintain stable along years (1999-2004) and also within grafted copies. On the other hand, the green intensity of shade side of fruits as well as the intensity of the red blush coloration of the majority of variants are influenced seriously by year to year climatic conditions but also by the age of trees.
