|LEE, RICHARD - Retired ARS Employee
|RAMADUGU, CHANDRIKA - University Of California
Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/24/2020
Publication Date: 5/1/2021
Citation: Lee, R., Keremane, M.L., Ramadugu, C. 2021. Use of young plants for biological indexing of graft transmissible pathogens of citrus. Crop Protection Journal. 143. Article 105524. https://doi.org/10.1016/j.cropro.2020.105524.
Interpretive Summary: Germplasm collections provide sources of diversity needed for crop improvement. However, introduction of germplasm from around the world requires to be don cautiously to avoid introduction of diseases. Imported citrus germplasm are therapied and tested using both biological and laboratory methods prior to their release from quarantine. Her, we describe an alternative for standard bioindexing through the use of very young plants as indicators which facilitates pathogen detection with the same sensitivity as the standard method, but with much lesser time, greenhouse space and cost.
Technical Abstract: In budwood certification programs, commonly used technology-based laboratory methods for detecting known citrus pathogens need to be complemented with biological indexing to confirm the absence of known and unknown graft transmissible pathogens (GTPs). We report here a procedure for biological indexing using very young indicator plants, 75-90 days old. Assay results of traditional biological indexing and mini-plant indexing conducted for 51 quarantine accessions and 29 positives infected with known pathogens were compared. The evaluation indicated the same level of sensitivity of detection between the two methods. Traditional bioindexing requires premium greenhouse resources and a lengthy incubation period; the use of mini-plants for indexing can provide a viable alternative since the technique can be conducted with a fraction of the resources typically needed. We were able to index for GTP requiring cooler temperatures during summer in southern California by placing mini-bioindicator plants near the cooling pads in an evaporatively-cooled greenhouse. Indicator plants kept under favorable conditions expressed symptoms throughout the year. Limited greenhouse space is required due to the small size of the indicator plants, and they can be used for biological indexing within three months as compared to 9-12 months with traditional indicator plants. Young plants require much less space with 240 plants/m2 of bench space as compared to 30 plants/m2 using the conventional approach for biological indexing. The use of mini-plant biological indexing will enable citrus ‘clean stock’ and/or certification programs to function more efficiently with limited resources and facilities.