ARS Scientists Seek Solution for Black Raspberry Decline

For decades, 'Munger' has been the black raspberry cultivar of choice for the Pacific Northwest, where most of the nation's black raspberries are grown. In the 1990s, however, the plants started losing vigor, forcing growers to seek hardier alternatives. So scientists with the Agricultural Research Service (ARS) have been working to identify the problem's origin and develop control strategies.

ARS plant pathologist Bob Martin has discovered several viruses that may contribute to the berries' poor health. The most significant is black raspberry necrosis virus (BRNV), which has been present in all observed cases with disease symptoms. The severe form of decline is always accompanied by another virus—raspberry bushy dwarf virus, raspberry mottle virus (RMoV), or black raspberry latent virus—or some combination of the three.

Martin, based at the Horticultural Crops Research Unit in Corvallis, Ore., and his colleagues have identified the raspberry aphid as a major culprit in the spread of BRNV and RMoV. Knowing how aphids transmit the diseases is essential for developing control strategies.

One potential solution could be to surround black raspberry fields with "trap plants" that also appeal to raspberry aphids, but are not susceptible to this severe decline. Instead of spraying the entire field, growers could simply treat the brdering plants with a low-toxicity pesticide.

Another solution could involve breeding disease- and insect-resistant black raspberry plants. Corvallis plant geneticist Chad Finn and his colleagues collected and assessed 16 different commercial cultivars from commercial nurseries and the ARS National Clonal Germplasm Repository.

The team then crossed the most promising plants and examined their offspring. Analysis of the initial crosses revealed a dearth of diversity, with one notable exception. A pair of wild plants from North Carolina consistently produced vigorous, healthy offspring that seemed to be less susceptible to disease than the other plants in the study.

The results suggest that it is possible to breed black raspberries for improved characteristics, but the process could be slow and would likely benefit from the introduction of wild germplasm.

Read more about this research in the January 2008 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief in-house scientific research agency.