Corky Net of Jostaberry
Physiological Disorder?

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 comments.

J.Postman 11/95