|Author: ||E. Germain|
Cultivated walnut varieties, generally well adapted to climatic conditions of the different production zones, often lack some important agronomic characteristics.
It would therefore be useful to select in natural populations or create through hybridization new cultivars combining characters of improved climate adaptation, early fruiting, high productivity, disease tolerance and quality fruit production.
This is possible given the very large and so far unexploited variability within the Juglans regia L. species.
Research carried out on walnut genetics at UC Davis (USA) and at the Fruit and Vine Research Station in Bordeaux (France) has led to the study of several tree and fruit quantitative characters.
Hybridization programs to create walnut varieties are relatively less developed than those of other fruit species.
However three main breeding programs carried out in California, France and Hungary have led to the release of twenty new lateral fruit bearing varieties.
Two recent programs to create vigorous and cherry leaf roll virus tolerant rootstocks but also CLRV - hypersensitive cultivars, are being developed at Davis and Bordeaux.
These programs are using interspecific hybridization's between Black Walnuts and Juglans regia L. followed by back-crosses with the latter species.
Some of these rootstock clones multiplied in vitro are currently being assessed.
The tools of biotechnology began to be used at Davis (USA) and Orléans (France) to transform the Persian walnut and particularly to introduce resistance to insect pests or cherry leaf roll virus.
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