Four sequential filters constrain the efficacy of spray-induced gene silencing against fungal pathogens

Fungal pathogens remain a major constraint on crop production, while resistance and residue concerns increasingly limit reliance on conventional fungicides. Spray-induced gene silencing (SIGS), an RNA interference (RNAi)-based approach, offers a non-transgenic and sequence-specific strategy for controlling fungal diseases. Although laboratory studies increasingly report effective gene silencing and disease suppression, these results have not consistently translated into reliable protection under field-relevant conditions. In this review, we examine this gap through four sequential filters: environmental persistence, pathogen-site exposure, fungal cytosolic delivery, and RNAi machinery availability. We critically review the evidence relevant to each filter and assess how its importance varies among fungal pathosystems. Comparisons with commercially advanced RNAi products targeting non-fungal organisms illustrate how protected delivery and controlled exposure can mitigate several barriers to efficacy. This framework provides a practical basis for identifying pathosystem-specific bottlenecks and guiding the development of more reliable RNAi-based fungicides.