Silver Nanoparticles Reduce Anthracnose Severity and Promote Growth of Bean Plants (Phaseolus vulgaris)

The present study aimed to evaluate the effect of silver nanoparticles (AgNPs) on the development of Colletotrichum lindemuthianum, the progression of anthracnose symptoms, and the growth of common bean plants. For this purpose, the fungal mycelial growth and conidial germination were assessed at AgNP concentrations of 0, 10, 30, and 50 mg·L−1 after seven days of incubation, as well as at 0, 0.1, 0.5, 1, 10, 30, and 50 mg·L−1 after 72 h, respectively. Bean plants of the IPR Uirapuru cultivar were sprayed at the V3 growth stage with AgNPs at 0, 10, 30, or 50 mg·L−1, either two days before, on the day of, or two days after inoculation. Conidial germination and appressoria melanization were measured on the leaf discs collected 24, 48, and 72 h after inoculation, and disease severity was assessed at 7 and 12 days post-inoculation. Another set of bean plants grown under the same conditions was used to evaluate growth promotion by AgNPs. For this, the plants were sprayed twice (with a seven-day interval), starting at the V3 growth stage, with AgNPs at 0, 10, 30, or 50 mg·L−1. Seven days after the second treatment, plant length and the fresh and dry weights of shoots and roots were measured, and the foliar pigments were quantified. The AgNPs did not reduce mycelial growth but completely inhibited the germination of C. lindemuthianum conidia. The severity of anthracnose decreased with the AgNPs in a dose- and application time-dependent manner, with the highest reduction (90%) observed when applied on the same day as an inoculation at 50 mg·L−1. This was strongly linked to a 70% decline in conidia germination and appressorium melanization on bean leaves. AgNPs at 50 mg·L−1 promoted plant growth by increasing the total length by 3%, as well as the fresh weights of bean shoots and roots by 17% and 90%, respectively, but did not affect the content of leaf pigments.