The reactions of Tayberry and nine of the most recently introduced UK red raspberry cultivars to each of nine viruses commonly found in the UK are presented. New sensitive indicator plants for detecting raspberry yellows disease (induced by raspberry bushy dwarf virus) and for rubus yellow net virus are reported.
In tests made under a voluntary quarantine scheme for imported Rubus material at SCRI, Dundee, a virus new to red raspberry was detected in the cv. Tweddell imported from Quebec, Canada. The virus is serologically related to cherry rasp leaf, a virus transmitted by Xiphinema americanum and previously found only on the western seaboard of North America. No symptoms developed in graft inoculated plants of several common Rubus indicator species or in red raspberry cultivars.
Several apparently unrecorded virus-like disease symptoms were observed in raspberry and bramble cvs in Britain. A graft transmissible agent isolated from a single plant of a red raspberry selection from southern England induced a severe curling of young leaves of Norfolk Giant raspberry. The plant contained raspberry bushy dwarf virus but was free from other detectable viruses including that of (American) raspberry leaf curl.
The commonest virus-like symptom observed in plants of the bramble cvs Bedford Giant, Bedford Thornless, Boysen, Chehalem and Marion is a chlorotic mottling of the leaves, particularly of fruiting cane; plants frequently show a degeneration in vigour. Many affected Bedford Giant and Bedford Thornless plants contained viruses that induced symptoms in Rubus indicator plants typical of black raspberry necrosis (BRNV), raspberry leaf mottle (RLMV) and raspberry leaf spot (RLSV) viruses, but only BRNV was detected in all affected plants. Whether this virus is the cause of the disease is not known.
A different disease symptom has been found affecting Tayberry plants in a few plantations in Scotland. Leaves develop large chlorotic blotches or rings and, in severely affected plants, leaves of primocanes are poorly developed and plants show decreased vigour. Many such plants contained BRNV, RLMV and RLSV.