Scientists from the University of California and team successfully conferred
virus tolerance to citrus using a combination of traditional and modern
biotechnological techniques. The results are reported in Transgenic
Research.

One of the problems of citrus growers is citrus psorosis virus (CPsV).
Citrus lack naturally occurring resistance to this virus, and thus
scientists from the University of California and team assembled citrus
plants by grafting, combining a non-transgenic Sweet Orange as scion,
CPsV-resistant transgenic Sweet Orange lines expressing intron-hairpin (ihp)
RNA derived from the viral coat protein (ihpCP) as interstock, and a
non-transgenic citrus as rootstock. Results showed that ihpCP-transcripts
translocate through the graft from interstock to scion, triggering the
silencing of coat protein mRNA target.

Further analysis showed that expression of ihpCP in the interstock provides
resistance against CPsV in the interstock, and different levels of
protection in the non-tg scion, depending on the virus delivery site.

[link.springer.com]