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ARS Home » Northeast Area » Washington, D.C. » National Arboretum » Floral and Nursery Plants Research » Research » Research Project #425046

Research Project: Biotechnology Applied to High Value Ornamental Plants

Location: Floral and Nursery Plants Research

2018 Annual Report

This project applies biotechnology to effectively mitigate the impact of pests and pathogens on priority floral crops and develops systems that can be manipulated to preserve select hardwood tree taxa for future genetic engineering applications. Genetic engineering of floral crops for pest and pathogen resistance contributes to sustainable production. There has been little research done on migratory nematodes such as Pratylenchus, and this project addresses the use of transgenes that may be effective in controlling Pratylenchus. Viruses are always a problem for propagated plants, particularly flower bulb crops that are propagated from the same bulb for many years. This project determines if an RNAi approach is effective for control of Cucumber mosaic virus (CMV), an economically important virus that affects numerous crops. In vitro manipulation of plants through genetic engineering allows for rapid clonal propagation, ploidy level manipulation, and preservation of germplasm and cryopreservation. Hardwood trees have been difficult to manipulate in vitro, and there are few reports of research done with North American hardwood tree taxa. This project will explore the possibilities of regenerating plants from select oak, elm, or maple taxa for future applications by using either embryogenesis or organogenesis and maintaining plants in vitro by micropropagation. Objective 1: Characterize the interaction between Pratylenchus and transgenic Easter lilies transformed with currently available anti-nematode genes for resistance response. (NP301; C1, PS 1B) Objective 2: Identify genes involved in the metabolic activities of Pratylenchus, using an RNAi approach, and determine if they are effective in enhancing resistance to Pratylenchus, using a soybean hairy root system. (NP301; C1, PS1B) Objective 3: Develop and evaluate lilies containing an antiviral gene for resistance to Cucumber mosaic virus. (NP301; C1, PS 1B) Objective 4: Develop a regeneration system from embryogenic callus for priority hardwood tree species in the tree improvement program at the U.S. National Arboretum. (NP301; C3, PS 3B)

Genetic engineering will be used to introduce genes into Easter lily for nematode and cucumber mosaic virus resistance. Genes that will be tested for nematode resistance are two Bt genes and a cystatin genes. Two genes targeting nematode movement will be used in an RNAi approach against the root lesion nematode. Seeds and cuttings from select hardwood tree species will be cultured in vitro and used for micropropagation and induction of callus. Treatments will be used to determine if plants can be regenerated from the callus.

Progress Report
This is the final report for the Project 8020-21000-058-00D which ended February 13, 2018. The new NP301 OSQR approved project 8020-21000-068-00D entitled “Biotechnology Applied to Ornamental Plants for Controlling Migratory Nematodes” began February 14, 2018. Progress was made on all four objectives during the five years of this project. Under Objective 1 the mas2 promoter was found to direct gene expression preferentially in roots of lilies making it a useful promoter when engineering lilies for root lesion nematode resistance. Lilies were transformed with the cystatin gene and found to be resistant to root lesion nematodes in vitro. Under Objective 2, a second approach to nematode resistance was to target nematode-specific parasitism genes for silencing. Gene sequences were obtained from root lesion nematodes, and 22 parasitism genes were identified. Eight metabolic genes and 7 parasitism genes of root lesion nematodes were targeted for silencing in hairy roots of soybean. Several of these targeted gene sequences reduced nematode reproduction, showing that they can be used as a new technology for controlling root lesion nematodes. Two parasitism genes have been selected for engineering lilies for nematode resistance. Lilies have also been engineered with a gene that targets Cucumber Mosaic Virus to prevent is replication (Objective 3). Under Objective 4, regeneration and micropropagation systems were developed for a priority hardwood tree species, Chinese elm, at the U.S. National Arboretum. Micropropagation and regeneration of trees can contribute to the USNA breeding program because they can be used to maintain elite clones, and seeds of elms are not ideal for storing elm genotypes.

1. New technology for root lesion nematode resistance in plants. The root lesion nematode, Pratylenchus penetrans, ranks third among nematodes for the economic loss that it causes to crops. ARS researchers in Beltsville, Maryland, identified a sequence for a parasitism gene specific to nematodes and expressed this gene in soybean roots. The expression of this gene resulted in inhibited reproduction of root lesion nematodes. This technology can be applied to genetic improvement of plants that are susceptible to root lesion nematodes such as potatoes, soybeans, corn, fruits crops, and lilies. The technology can decrease the use of chemicals to control nematodes; because it is nematode-specific, it will not affect non-target organisms such as insects, birds, and humans.

Review Publications
Vieira, P., Mayer, T., Eves-Van Den Akker, S., Howe, D., Zasada, I., Baum, T., Eisenback, J.D., Kamo, K.K. 2018. Identification of candidate effector genes of Pratylenchus penetrans. Molecular Plant Pathology.
Lakshman, D.K., Kamo, K.K. 2018. First report of lily root rot caused by Thantephorus cucumeris AG 2-1 in the United States. Plant Disease.