Chestnut mosaic from Japan
Plant breeders in France have imported Castanea crenata from Japan as a major parent of interspecific hybrids with the European chestnut Castanea sativa. These hybrids are intended for use as rootstocks with resistance to various diseases. Since these importations, European chestnuts grafted on hybrid rootstocks have been found to be affected by a new disease, Chestnut mosaic, presumably introduced from Japan. The exact etiology is not known, but the disease is evidently graft transmissible, and apparently spreads by above ground means also. The mosaic symptom is seen on C. crenata itself, while C. sativa remains symptomless. However, an infected C. sativa scion grafted on a susceptible rootstock will contaminate it, and, the whole plant will then decline.
Sources
INRA & CTIFL, France (1992-05)