Corky Net of Jostaberry
The foliar symptoms shown here are
produced almost annually on the blackcurrant-gooseberry hybrid known as
Ribes nidigrolaria Bauer "Jostaberry". In our collection of
several hundred Ribes species and cultivars, only Jostaberry and
open pollinated seedlings of this plant have produced these symptoms.
From a distance, this resembles damage caused by a leaf-miner, but we have
found no insect or pathogen associated with the disorder. We have been
unable to isolate a fungus or bacteria from affected leaves, nor are
fungal tissues apparent in microscopic examinations. Tests for viruses
have so far been negative. Plants have been observed to produce this
network of raised corky tissue following cool periods during the growing
season, and to produce normal foliage when the weather gets warmer.
Plants growing in a screenhouse have produced symptoms simultaneously with
plants growing in several diverse field locations in western Oregon.
We are presuming this to be a physiological disorder of this particular
genotype. Anyone having suggestions as to a possible cause of this
disorder, or wishing to examine some actual leaves during the next growing
season is invited to send