Black currant reversion disease--the probable causal agent, eriophyid mite vectors, epidemiology and prospects for control.

Black currant reversion disease and the vector of its causal agent, the black currant gall mite Cecidophyopsis ribis, have been recognised for at least 100 years and are the two most damaging organisms of black currant crops world-wide. However, the molecular characterisation of these two organisms has begun to be determined in only the last few years. The probable causal agent of reversion disease, Black currant reversion associated virus (BRAV), belongs to the genus Nepovirus, has isometric particles c. 28 nm in diameter that contain a single major polypeptide of c. 55 KDa and two polyadenylated ssRNA species of 7700 nt and 6400 nt. Some particle preparations also contain a satellite ssRNA species of 1432 nt. Using immuno-capture RT-PCR and primers based on the genomic RNA of BRAV, this virus was shown to be closely associated with reversion disease. Analysis of Cecidophyopsis mite rDNA, identified rapidly and unambiguously the three known species on Ribes and distinguished four new ones. Resistance to the reversion agent and to the gall mite vector has been introduced into black currant and has given effective control of these respective organisms in the field. These findings and their significance for the ecology, epidemiology and control of variants of these two organisms are reviewed and discussed.