3.3.1. Agar Well Diffusion Assay

Post three days of incubation, the prepared ZnNPs were evaluated for five different concentrations (0, 5, 10, 20, and 40 mg mL −1 ) to exhibit an inhibitory effect on the mycelial growth for all three test fungi. Among the three fungal cultures, maximum mycelial inhibitory activity was recorded in order *Fusarium oxysporum* > *Curvularia lunata* > *Macrophomina phaseolina* (Figure 7). The efficacy of the NaOH (RA) derived ZnNPs was identified by the formation of a larger inhibition zone compared to the other ZnNPs evaluated. The control well containing only sterilized HPLC grade water did not exhibit any antifungal activity (Figure 7). The radial diameter of all the three-test fungi was the smallest for the NaOH (RA) derived ZnNPs particularly clear cottony-white hyphal inhibition could be observed for *Macrophomina phaseolina* (Figure 7d). Moreover, the sparse, aerial, and fluffy fungal growth of the *Fusarium oxysporum* indicates the response of hyphae to ZnNPs stress. This is the first report on variability in the anti-mycotic efficacy of the ZnNPs derived from different reducing/complexing agents on maize crop-specific pathogenic fungi.

**Figure 7.** Effect of different ZnNPs and zinc salts on hyphal growth of three maize pathogenic cultures, Curvularia lunata, Fusarium oxysporum, and Macrophomina phaseolina. (**a**) Zinc acetate, (**b**) Zinc chloride, (**c**) Zinc sulphate, (**d**) Sodium hydroxide (RA) ZnNPs, (**e**) Thiourea (RA) ZnNPs, (**f**) Starch (RA) ZnNPs, (**g**) Bovine serum albumin (CA) ZnNPs, (**h**) Starch (CA) ZnNPs, and (**i**) Cellulose (CA) ZnNPs. The figures from 0 to 4 indicate different concentrations of the zinc salts and ZnNPs. 0 = distill water, 1 = 5 mg L −1 , 2 = 10 mg L −1 , 3 = 20 mg L −1 , 4 = 40 mg L −1.
