Baseline Sensitivity of Alternaria alternata and A. arborescens to Natamycin and Control of Alternaria Rot on Stored Mandarin Fruit

Altemaria rot caused by Alternaria alternata and A. arborescens is one of the major postharvest diseases on mandarin fruit in California. In this study, natamycin, a newly registered biofungicide, was evaluated for its potential as a postharvest treatment to control Altemaria rot on mandarin fruit. The baseline sensitivities of A. alternata and A. arborescens to natamycin were determined. Effective concentration inhibiting 50% of fungal growth (EC50) values of natamycin for 70 A. alternata isolates ranged from 0.694 to 1.275 mu g/ml (mean = 0.921 mu g/ml) in a conidial germination assay and from 2.001 to 3.788 mu g/ml (mean = 2.797 mu g/ml) for 40 A. alternata isolates in a mycelial growth assay. EC50 values of natamycin for 30 A. arborescens isolates ranged from 0.698 to 1.203 mu g/ml (mean = 0.923 mu g/ml) in a conidial germination assay and from 2.035 to 3.368 mu g/ml (mean = 2.658 mu g/ml) for 20 A. arborescens isolates in a mycelial growth assay. Control tests on detached mandarin fruit showed that natamycin at both low (460 mu g/ml) and high (920 mu g/ml) recommended rates significantly reduced disease incidence and severity on mandarin fruit inoculated with Alternaria isolates, regardless of species. High rate of natamycin significantly reduced disease incidence and severity compared with the nontreated control even when natamycin treatment was delayed for 6, 12, and 18 h after inoculation. Our results suggested that natamycin can be an effective postharvest fungicide for control of Alternaria rot on mandarin fruit.

Automated summary

The study evaluated the potential of natamycin as a postharvest treatment for controlling Alternaria rot on mandarin fruit. The results indicated that natamycin was effective in reducing disease incidence and severity, even when the treatment was delayed after inoculation.