Topical application of double stranded (ds) RNA for control of Plant Pathogens and Pests
Authors: Basavaprabhu L. Patil^*, S. V. Amitha Mithra and Amolkumar U. Solanke
ICAR-National Research Centre on Plant Biotechnology, IARI, Pusa, New Delhi
^*Corresponding author: blaptil2046@gmail.com

The discovery of RNA-interference (RNAi) or Gene Silencing phenomenon has revolutionized the area of Biotechnology or Molecular Biology. RNAi-technology is successfully being employed for developing transgenic crop plants with desirable traits, particularly for the management of plant diseases and pests. However, due to certain ethical issues associated with the release of transgenic or genetically engineered crops, particularly in the case of India, the acceptance and cultivation of different transgenic crops is difficult to be realized in the present time. To reduce the concerns with regards to the safety of environment and the food, plant biologists are exploring alternative technologies that can trigger strong disease resistance without engineering plants containing the foreign DNA or transgene. Hence, biotechnological interventions not involving development of transgenic plants are ideal alternatives for control of plant diseases, such as the diseases caused by plant viruses. Interestingly, in contrast to transgene derived pathogen resistance, the RNAi can be readily induced through foliar/topical spray application of double-straned (ds)-RNA molecules. The dsRNA is central to the induction of the RNAi pathway in both transgenic or in naturally virus infected plants, which eventually result in production and accumulation of small interfering (si)-RNAs. Thus the advancements in the dsRNA expression systems and improvements in the application of dsRNA as a 'spray-on' technology for non-transgenic induction of pathogen/pest resistance is very important and promising for the control of plant diseases or any other plant pests/insects.

Currently several dsRNA synthesis systems are available for producing the large amounts of dsRNA required for foliar/topical application on the crop plants. However, currently there are also some limitations for the spray-on or foliar application of dsRNA for field application. Thus continued research to define a new phase in the non-transgenic delivery of RNAi for complete management of plant pathogens/pests is crucial for its successful commercialization. Currently, this approach is still in experimental stage, however when appropriate experimentation and production capacities are accomplished, the dsRNA-based technology has the potential to revolutionize crop protection, with an ultimate goal of enhancing crop yields.

Recently a nano-formulation for the topical/foliar delivery/application of the dsRNA and also enhance the stability and durability of dsRNA on plant foliage has been reported by scientists from University of Queensland (Australia), published in the January 2017 issue of the journal Nature Plants
.

The dsRNA molecules can be firmly coated on a naturally occurring non-toxic and degradable Layered Double Hydroxide (LDH) clay nanosheets, which are not washed off and the dsRNA are gradually released for over a period of 2-30 days of its application. This was successfully demonstrated for control of plant viral diseases through dsRNA application; this innovation helps in the commercial exploitation of dsRNA based virus control strategy in crop plants. In addition to the control of plant viruses this technology could also be employed for effective implementation of RNAi for control of other plant pests and pathogens.

References:

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