Baseline sensitivity of Alternaria alternata and A. arborescens to natamycin and control of alternaria rot on stored mandarin fruit

Authors: WANG, F - Kearney Agricultural Center; Saito, Seiya; MICHAILLIDES, THEMIS - Kearney Agricultural Center; Xiao, Chang-Lin

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2021
Publication Date: 11/18/2021
Citation: Wang, F., Saito, S., Michaillides, T.J., Xiao, C. 2021. Baseline sensitivity of Alternaria alternata and A. arborescens to natamycin and control of alternaria rot on stored mandarin fruit. Plant Disease. 105(11):3653-3656. https://doi.org/10.1094/PDIS-04-21-0809-RE.
DOI: https://doi.org/10.1094/PDIS-04-21-0809-RE

Interpretive Summary: Alternaria rot caused by Alternaria alternata and A. arborescens is one of the major postharvest diseases on mandarin fruit in California. Natamycin, a recently registered biofungicide, was evaluated for its potential as a postharvest treatment to control Alternaria rot on mandarin fruit. In the assays with agar media amended with natamycin at various concentrations, natamycin was effective against both Alternaria species, and the effective concentrations of natamycin that inhibit fungal growth by 50% relative to the control were established for the two species. Control tests on mandarin fruit showed that natamycin at both low (460 µg/ml) and high recommended rates (920 µg/ml) significantly reduced Alternaria rot on mandarin fruit inoculated with Alternaria isolates, regardless of species. High rate of natamycin significantly reduced disease compared to the non-treated control even when natamycin treatment was delayed for 6, 12, and 18 hours after inoculation. Our results suggested that natamycin can be an effective postharvest fungicide for control of Alternaria rot on mandarin fruit.

Technical Abstract: Alternaria rot caused by Alternaria species is one of the major postharvest diseases on mandarin fruit in California. Natamycin, a biofungicide, was evaluated for its potential as a postharvest treatment to control Alternaria rot. The baseline sensitivities of two Alternaria spp., A. alternata and A. arborescens, collected from stored mandarin fruit were established. EC50 values of natamycin for 70 A. alternata isolates ranged from 0.694 to 1.275 µg/ml with a mean of 0.921 ± 0.133 µg/ml for conidial germination, and from 2.001 to 3.788 µg/ml with a mean of 2.797 ± 0.431 µg/ml for 40 A. alternata isolates for mycelial growth. EC50 values of natamycin for 30 A. arborescens isolates ranged from 0.698 to 1.203 µg/ml with a mean of 0.923 ± 0.137 µg/ml for conidial germination, and from 2.035 to 3.368 µg/ml with a mean of 2.658 ± 0.389 µg/ml for 20 A. arborescens isolates for mycelial growth. Control tests showed that natamycin at both low (460 µg/ml) and high recommended rates (920 µg/ml) 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 to the non-treated control even when natamycin treatment was delayed for 6, 12, and 18 hours after inoculation. Our results suggested that natamycin can be an effective postharvest fungicide for control of Alternaria rot on mandarin fruit.