ADVANCES IN WALNUT BREEDING AND CULTURE IN THE UNITED KINGDOM

Walnut (Juglans spp.) has not been widely cultivated for timber or fruit production in the United Kingdom (UK). Recent research activities in the UK have stimulated renewed interest in common walnut (J. regia), black walnut (J. nigra) and hybrids as providers of valuable timber on relatively short rotations, and in the case of J. regia, as a highly marketable fruit crop. In addition, these walnut species are likely to be more suitable than many native tree species to the climatic conditions predicted for the UK within a single generation. A substantial collection of walnut germplasm has been established through complimentary research programmes at the Northmoor Trust (NMT) and East Malling Research (EMR).
The NMT programme has concentrated on J. regia for timber production. Genotypes were collected across 11 countries from both the introduced and natural ranges of the species, amassing a total of 371 half-sib progeny, primarily from the walnut-fruit forests of Kyrgyzstan. Five-year results for survival, growth and phenology from the trials are presented, indicating significant variability for growth and phenology. A series of silvicultural trials have been established aimed at improving establishment and early growth of walnut species in the UK. The programme at EMR has focussed on establishing a clonal collection of 78 timber selections (J. regia, J. nigra, J. major, and their hybrids) and 66 J. regia fruit varieties from breeding programmes across Europe and the United States of America (US). Jointly, NMT and EMR have initiated a black walnut timber improvement programme, comprising seedling progeny from 7 European countries and 13 States in the US. The genetic resource within these combined programmes provides an unrivalled resource for breeding and genetic improvement both for timber and fruit production, and for genetic diversity and adaptive trait studies.