This work has resulted in the development of advanced breeding lines that do not appear to have the yield reductions associated with commercial snap bean cultivars. Selection of this resistance is currently being made in market types. Successful incorporation of this resistance could prevent significant reductions in yield caused by cucumber mosaic virus infection (estimated at $2.6 million for New York processing snap beans alone in 2007).
Pyramiding CMV resistance with bean yellow mosaic virus resistance and clover yellow vein virus resistance will enable the development of snap bean varieties with high levels of host plant resistance to additional problematic viruses. The annual savings to New York snap bean producers if successfully incorporated into market types would exceed $1 million/year.
impact statement issue
In 2001, serious yield losses in snap bean were associated with aphid-transmitted virus, particularly in the western New York counties (largely associated with the Asian soybean aphid, which first appeared at this time). The primary virus causing yield loss is CMV, which causes flower reduction and distortion when vectored to snap bean fields pre-bloom.
Since 2001, CMV has continued to inflict devastating losses in snap bean production areas, threatening the future viability of this crop, and all affiliated industries in New York state.
As the aphid-vectors do not complete their life cycle on snap beans, it is not possible to control the spread of this virus using chemicals, and there are no common bean varieties that are resistant to CMV. Without introduction of snap bean varieties with host-plant resistance, the future production of this crop in New York is in doubt. A breeding initiative started in 2001 to develop virus-resistant snap beans.
impact statement response
Resistance to cucumber mosaic virus was identified in scarlet runner bean accessions in 2002 following selection of symptom-less plants. This resistance is multiple gene and may be incomplete. However, it appears to be sufficient to prevent the yield losses attributed to CMV infection. These losses occur following pre-bloom infection with the virus resulting in a reduced flower number and a distortion of pistils within the flower, preventing pod-set.
Several interspecifc hybrids were recovered from crosses with enzyme-linked immunosorbent assay negative scarlet runner bean accessions between 2002-2004, and they were used to develop backcross populations with snap bean (in particular 'Hystyle') for transfer of CMV resistance.
These populations have been used to transfer the resistance into commercial snap bean types. Backcross populations created from these crosses have been evaluated for CMV resistance between 2003 and 2007, and advanced through a large greenhouse screening effort, evaluating foliar symptoms in early trifoliates, and pod set and plant type following flowering.
A combination of sources from different backcross populations are being focused on for development of resistant varieties and study of CMV resistance. Combining the sources has resulted in a higher level of resistance, indicating that the genes in the different populations may not all be allelic. Initial studies of yield loss indicate that breeding lines do not experience the reduced pod set that occurs in commercial snap bean varieties.
impact statement summary
Aphid-transmitted viruses have been causing considerable yield losses in snap bean plantings throughout the Northeast since 2001. These are associated with a new vector, the Asian soybean aphid.
The most important virus that is transmitted is cucumber mosaic virus (CMV), which has been detected through enzyme-linked immunosorbent assay in close to 100 percent of infected fields and has been shown to be directly responsible for yield losses following pre-bloom infection. This yield loss results from a reduction of flower number and/or flower distortion in infected plants. Other viruses including bean yellow mosaic (BYMV), and clover yellow vein (CYVV) cause further problems.
Aphids do not complete their life cycle on snap beans, making chemical control close to impossible. Resistance to CMV was identified in the related species scarlet runner bean. Breeding lines have since been developed following inter-specific crosses with scarlet runner bean, the control of which appears to be based on at least two genes.
Combination of two breeding lines has enhanced this resistance, and this material is being used to improve the plant type, such that CMV resistance can be incorporated into commercial snap bean lines. BYMV and CYVV resistance genes have been used to generate crosses and segregating populations in order to select resistance and to pyramid these genes with CMV resistance.
Other private funding
New York State Integrated Pest Management Program, Pennsylvania Vegetable Research Association, Specialty Crop Block Grants
