Cowpea leaf and pod spots caused by Periconia igniaria and their potential control using biosynthesized zinc oxide and magnesium oxide nanoparticles

Cowpea is subject to attacks by a wide range of plant pathogens including bacteria, fungi, viruses, and nematodes. In this study, a field survey was conducted in cowpea growing regions of El-Minya Governorate of Egypt including Minya, Beni Mazar and Maghagha districts for leaf and pod spot disease. Our results revealed that the disease was present in all surveyed fields with the highest disease incidence and severity found in Minya District. For the first time in Egypt, the causal agent of the disease was determined to be Periconia igniaria based on morphology of the fungal isolates, internal transcribed spacer sequence homology to a P. igniaria strain, and fulfillment of Koch's postulates. To explore control measures, zinc oxide (ZnO) and magnesium oxide (MgO) nanoparticles (NPs) were synthesized biologically using green coffee extract. Both NPs were characterized, and their formulations confirmed using scanning electron microscopy and the energy spectrum dispersion analysis. The biosynthesized ZnO- and MgO-NPs were demonstrated to have antifungal activity against in vitro mycelium growth of P. igniaria at all tested concentrations from 25 to 200 ppm, and ZnO NPs were more effective than MgO NPs at the same concentration. When 100 ppm of ZnO NPs was tested in planta, it significantly reduced disease incidence and severity in detached cowpea leaves and pods under laboratory conditions, and in cowpea plants under greenhouse conditions. Our results demonstrated that the biosynthesized ZnO NPs have great potential to be developed into an effective and eco-friendly control method against cowpea disease caused by P. igniaria.