Enhancing the sustainability of fresh-market snap bean production in the Northeast by identifying and promoting cultivars with tolerance to Cucumber mosaic virus (CMV).

Enhancing the sustainability of fresh-market snap bean production in the Northeast by identifying and promoting cultivars with tolerance to Cucumber mosaic virus (CMV).

Summary

The project has completed initial characterization of symptom expression in response to infection with Cucumber mosaic virus (CMV), as well as Bean yellow mosaic virus (BYMV) in a large and diverse panel of snap bean cultivars. None of the snap bean cultivars evaluated remained asymptomatic, suggesting that complete resistance to these viruses is not available in snap bean germplasm. The patterns of symptom expression were defined and documented and a cultivar response booklet was produced. The severity of symptom expression varied significantly, and allowed for a subset of 14 cultivars to be selected for severe symptom expression and 26 cultivars for mild symptom expression in response to CMV. Due to unfavourable timing and inadequate seed, the two subsets of snap bean cultivars were planted in a preliminary field experiment that was designed to provide invaluable experience and information. The experience and information gained will be applied to successfully complete the field-based evaluation of tolerance to CMV in snap bean cultivars in the coming growing seasons.

Objectives/Performance Targets

The objectives remain identical to the original plan of work. The objectives are listed below followed by a brief description of what has been accomplished to date.

1. Characterize symptom expression in response to Cucumber mosaic virus (CMV) infection in a diverse group of snap bean cultivars

A panel of 115 snap bean cultivars representing varying origins, dates of release, and market classes was assembled. The first replication of the experiment to characterize symptom expression in response to CMV infection was carried out, and the response of each cultivar was assessed for symptom incidence, symptom type, and symptom severity. The disease screen was highly successful based on the high efficiency of inoculation (near 100%) and pronounced symptoms on all known susceptible controls and cultivars, with no symptoms evident in uninoculated controls. In addition to the stated objective, the panel of snap bean cultivars was also evaluated for response to infection with BYMV, another virus disease of increased prevalence in snap beans in the Northeast. As expected, there was a wide range of symptom expression in response to virus infection among the snap bean cultivars. Symptom severity varied from very mild to very severe, and allowed for the identification of snap bean cultivars with divergent symptom expression. None of the 109 cultivars screened however, lacked symptoms completely. Digital images of the first unfolded trifoliate leaf of uninfected, CMV infected, and BYMV infected snap bean plants of all 109 cultivars were obtained and compiled into a booklet for future reference (booklet not submitted). A second replication of the disease screen with both CMV and BYMV will be carried out during the spring of 2011 to confirm the results of the first and to screen any additional germplasm that can be made available. The methodology will change slightly in that plants may be inoculated in larger containers so that symptom expression can be monitored over a longer duration of growth. In addition, DAS-ELISA will be used to confirm infection efficiency in the 2011 screening.

2. Conduct field-based evaluation of agronomic characteristics and yield responses to CMV infection in a subset of snap bean cultivars with diverse symptom expression in order to:
-(2a.) Determine the impact of CMV infection on the yield of snap bean cultivars with a range of symptom expression.
-(2b.) Identify snap bean cultivars capable of producing acceptable yields and quality when infected with CMV.
-(2c.) Characterize the relationship between patterns of symptom expression and yield loss.

The overall purpose of this objective is to obtain accurate and objective data on the agronomic characteristics and yield of snap bean cultivars in response to CMV infection. 14 snap bean cultivars with severe symptom expression in response to CMV infection and 26 snap bean cultivars with milder symptoms were chosen based on the results of the first replication of Objective 1. 6 uninoculated plants of each of the 40 cultivars were moved into another greenhouse so that an attempt at producing an adequate amount of seed could be made for the first of the field experiments of Objective 2. Unfortunately, and due to the timeframe under which the project was conceived, planned, and initially implemented and funded, adequate amounts of seed for the complete experiment could not be produced and/or obtained within a favorable time frame. Instead, a preliminary field experiment was conducted with a modified experimental design in order to gain preliminary experience and information for carrying out this type of field experiment for future growing seasons.
The preliminary field experiment of 2010 was planted as two separate randomized complete block designs where each experiment included 3 complete blocks of all 40 cultivars randomized and planted as 4 row-foot plots, and where one experiment was inoculated with CMV and the other experiment was mock inoculated with buffer and Carborundrum only. In addition to the tight timeline and inadequate amounts of seed, the Field Research Unit at NYSAES received over 2 inches of precipitation in the week following planting on July 19, 2010. Unfortunately, the precipitation lead to poor emergence and poor stands for approximately 20% of the plots. Despite these setbacks, the plots were inoculated with CMV at 10 and 15 days after planting. Inoculation efficiency was assessed by a DAS-ELISA assay on 3 randomly sampled leaves from every plot of every cultivar in the experiment. Inoculation efficiency was 96% for the CMV inoculated experiment. The mock-inoculated experiment was not covered with floating row cover and the DAS-ELISA assay revealed that the virus was spread from the infected plots efficiently by vectors and/or other means as 73% of leaves sampled tested positive for CMV. The experiments were evaluated for symptom expression and severity as best as possible on a weekly basis and were harvested for yield data as late as was possible. It was decided to collect yield data based on physiologically mature plants rather than at optimal harvest maturity to account for any effect that CMV infection may have on development and maturation. Preliminary analysis of yield data is inconclusive due to the lack of replication and the extensive environmental variation. The modified experimental design also precludes the direct assessment of the impact of CMV on yield. The data available at this point is thus insufficient to address Objectives 2a.) through 2c.), but progress has certainly been made in determining how best to do so.

3. Publish and Disseminate Results

The results to date do not yet provide enough data for publication. The cultivar response booklet has been completed and was printed and shared with a number of snap bean growers and processing industry representatives from New York this past summer for their information.

Accomplishments/Milestones

The project has made significant progress within the relatively brief time period since the project start date and despite several setbacks. Through the completion of the first replication of Objective 1, the project has characterized the response to infection with CMV, as well as BYMV, of a large and diverse panel of snap bean cultivars. The results of this characterization suggest that none of the snap bean cultivars accessed and tested have complete resistance to CMV or BYMV. The second replication of Objective 1 will confirm this important result. With regards to the goals outlined by Objective 2, the work to date has not produced adequate nor appropriate data to address the goals. The work to date has however provided invaluable preliminary experience and insight for successfully completing Objective 2 in the near future. Because the field-based evaluation was unsuccessful at generating adequate and appropriate data, the approach and methods to completing Objective 2 will be changed slightly to include an additional location as well as larger plots, use of floating row cover, and additional replication for the split-plot experiments that will take place during the summer of 2011. This will be possible by overcoming the constraint of lack of adequate seed. Depending on the results and success of the 2011 season, an additional season of field-based evaluation may take place in 2012, or a greenhouse based yield evaluation will be included if possible and necessary to supplement the field data.

Impacts and Contributions/Outcomes

The project has thus-far demonstrated that although no snap bean cultivars appear to be resistant to CMV or BYMV, they do vary significantly in their response to virus infection and in how they express symptoms. The project will continue to access and evaluate additional snap bean germplasm, but it seems probable that the project will confirm that resistance to CMV and/or BYMV is not available in snap beans. If confirmed, this is an important impact in terms of being valuable information for both growers and those involved in snap bean improvement.
It is anticipated that such a diverse collection of cultivars will vary significantly for how CMV infection impacts yield. The project goals of determining this impact and in identifying snap bean cultivars that are capable of producing acceptable yield and quality when infected by CMV will eventually lead to accurate and objective information on which cultivars may be best to grow in areas that experience snap bean virus epidemics. It is hoped that such information will help to enhance the sustainability of fresh-market snap bean production in the Northeast by reducing the economic losses caused by aphid-transmitted virus epidemics.

Collaborators: