Dynamics of fusarium infection in melon crop and sirnas complexed with chitosan nanoparticles provide long-lasting protection against potato vírus y infection

Melon (Cucumis melo) is a globally important crop, and Brazil is one of its largest producers. The Northeast region is the primary melon-producing area in Brazil, with the states of Ceará (CE) and Rio Grande do Norte (RN) accounting for more than 77% of the total national production. This study aimed to clarify the dynamics of Fusarium infection in Cucumis melo. In 2022, two field experiments were conducted where different tissues of melon plants were evaluated at four distinct time points: E1: day of seedling transplant (root, stem, cotyledon); E2: 14 days after seedling transplant (root, stem, branch, leaf); and E3 and E4: 45 and 60 days after seedling transplant (root, stem, branch, leaf, and fruit), respectively. Additionally, flowers were isolated 28 days after transplant, and fruits were isolated 30 days after harvest. Seeds and substrates used for seedling production were also analyzed, and Fusarium was present in all plant tissues. In most of the sampled periods, the most significant number of fragments with Fusarium was found in the roots, as was the greatest species diversity. No Fusarium species were found in the seeds. Fourteen Fusarium species were identified: F. caatingaense, F. ipomoeae, F. longifundum, F. mucidum, F. sulawesiense (F. incarnatum-equiseti species complex - FIESC); F. spinosum (F. chlamydosporumspecies complex - FCSC); F. delphinoides (F. dimerum species complex - FDSC); F. verticillioides (F. Fujikuroi species complex - FFSC); F. contaminatum, F. kalimantanense, F. triseptatum (F. oxysporum species complex - FOSC); and F. falciforme, F. pseudensiforme, and F. silvicola (F. solani species complex - FSSC). All molecularly identified Fusarium species were pathogenic to fruits and seedlings, with species belonging to the FSSC complex being the most aggressive. We concluded that Fusarium has multiple infection routes in melons, affecting all plant parts, with the roots being the main point of entry for the fungus. These findings underscore the importance of a comprehensive disease management plan that focuses on pathogen-free substrates, reducing soil inoculum, and protecting flowers to control Fusarium infections in Brazilian melon production. Separately, potato virus Y (PVY) poses a significant threat to potato crops, with no viricidal solutions currently available. RNA interference (RNAi) is emerging as a promising tool for controlling plant viruses. However, effective delivery of siRNAs (one of the RNAi inducers) to plants is challenging, and chitosan nanocarriers stand out as a potential solution. We hypothesize that siRNAs complexed with chitosan nanoparticles applied to plants will suppress PVY infections. To test our working hypothesis, we designed siRNAs targeting the P1 cistron of the PVY genome, complexed them with chitosan nanoparticles, and applied the nanocomplex to tobacco plants. We then analyzed the PVY-treated plants at two distinct time points. Experiment 1: treatments and PVY inoculations were performed on the same day; Experiment 2: treatments were applied, and PVY inoculations were performed 10 days later. We evaluated disease severity and performed RT-qPCR (to measure viral transcripts) 14 days after PVY inoculations. We observed that when plants were treated with siRNAs and inoculated with PVY on the same day, the disease was suppressed regardless of whether the siRNAs were complexed with chitosan in nanocarriers or not. However, when plants were inoculated with PVY 10 days after siRNA applications, the complexed siRNAs suppressed the virus more efficiently than the uncomplexed ones. These results suggest that siRNA complexed with chitosan nanocarriers can provide long-lasting protection against target viruses, making it a promising tool for controlling viral infections in plants.