Detection and control of Alternaria black spot of tomatoes in the Western Cape of South Africa

The essential oil extracted from cloves (clove oil) and SO₂ (in the form of sulfur generating salts) were evaluated for efficacy to inhibit Alternaria alternata in vitro and tomato fruit. Alternaria spp. (either A. alternata or A. arborescens) are latent pathogens frequently isolated from tomatoes in the Western Cape of South Africa with a mean Alternaria spp. prevalence of 17.6% amongst isolates collected from postharvest decay symptomatic tomatoes.
Postharvest decay symptoms presented in the form of black spot.
Mycelial growth of the pathogen was partially inhibited (up to 67% reduced mycelial growth diameter) by clove oil volatiles (50% v/v concentration applied on filter paper inside a punnet containing petri dishes) or completely inhibited by SO₂ (1 g SO₂ generating salts in a sachet fixed to the lid of a punnet). Other tested SO₂ generating salts (sodium sulphate) were not found to inhibit mycelial growth of Alternaria spp. in vitro.
This study has demonstrated that the tomato pathogens Alternaria alternata and A. arborescens are sensitive to both clove oil and SO₂ in the form of sulphur generating salts (either potassium metabisulphite or sodium metabisulphite) incorporated in SO₂ sheets with complete inhibition of mycelial growth.

VI International Symposium on Pomegranate and Minor Mediterranean Fruits

C.K. Daniel-Swartland, J.C. Meitz-Hopkins, F. Vries, C.L. Lennox

antifungal, in vitro, packaging, SO₂, tomato (Solanum lycopersicum L.)

https://doi.org/10.17660/ActaHortic.2026.1464.47