**7. Conclusions**

Crop protection against pathogens and pest insects relies mostly on the widespread use of chemical pesticides that are applied to the environment in large amounts yearly; some of these chemicals are in use for almost half a century. Therefore, there is a need for novel tools more sustainable and less detrimental to the environment. Therefore, scientists have harnessed RNAi to turn off genes that they are studying. RNAi through nontransformative strategies will demand mass production of dsRNA, efficient delivery methods, and methods to validate its environmental stability.

A large number of studies have demonstrated the feasibility and efficacy of RNAi-based- approaches, and some transgenic plants have been approved for commercialization and release [38, 39, 79, 80]. However, unlike these strategies, which depend on plant transformation, the spray of dsRNA externally realizes crop protection without changing the plant DNA.-The- dsRNA-containing end-use products, nevertheless, will be differently regulated when compared to transgenic plants such as *Bacillus thuringiensis* crops. Moreover, chemical compounds- act through a structure-dependent mechanism, and dsRNA acts though a tailored species-specific sequence. Clearly, the dsRNA has more changes to act only against the target species. Also,- multiple target genes could be silenced simultaneously by fusing dsRNA sequences to generate a pyramidic plant protection approach, without any modification of the plant genome.-

It is worth to remind that a specific dsRNA exerts its mode of action throughout entire sequence length by generating a large pool of target-specific siRNAs [29, 30, 32]. This large pool of siRNAs for a single target increases target specificity and largely reduces evolution of mutations and resistance in the targeted organism. Indeed, the dsRNA is designed to match a long nucleotide sequences in the target organism (i.e., insects, pathogens, or viruses). The effectiveness of a long dsRNA will remain even when parts of this sequence mutate. So that it is believed that it is unlike to face resistance evolution that commonly makes a chemical pesticide ineffective. Resistance development toward RNAi has not been documented in insects and fungi, but as a famous artist says, "*life finds a way,*" these organisms have a great phenotypic and genetic plasticity and relatively short life cycle contributing for that some individuals/strains could be more or less sensitive to RNAi. For example, issues such as malfunction of dsRNA uptake or nuclease upregulation and/or processing dsRNA and systemic spread of RNAi signaling could stop the initiation and spread of RNAi response [45]. At least for arthropod species as recently reviewed [45], the potential degradation of dsRNA prior to ingestion, breakdown by nucleases in saliva and/or in the gastrointestinal tract, degradation of dsRNA in the hemolymph, and/or transport mechanisms of dsRNA within the organism are some of several barriers to physiological exposure that may lead to resistance.

The sprayed dsRNAs, different from regular pesticides, are biocompatible compounds as they occur naturally in the nature as well as inside/outside body of organisms and in food. The dsRNA ultimately is a regular RNA molecule that enters naturally within plants and other organisms. These molecules are subject of pathways from RNAi silencing mechanism, converted into siRNA and finally degraded by natural cell processes. In water and soil, dsR-NAs are rapidly degraded as regular RNA molecules do [81], so unlike to left considerably novel residues in food products.

New genomic tools will allow the development of technologies such as dsRNA sprays that increase crop resistance against insects, pathogens, and viruses; these could even replace chemical pesticides in some applications.
