Alternative Control of Alternaria Brown Spot in Tangerine

Abstract

Alternaria brown spot is considered the main disease of tangerines in the State of Paraiba. The objective of work was to evaluate vegetal tinctures from bitter melon (Momordica charantia) and guava (Psidium guajava) leaves, as an alternative control for Alternaria brown spot in tangerine. The effects of vegetal tinctures were tested in leaves and fruits (detached) of tangerine "Dancy" inoculated with tangerine pathotype of Alternaria alternata. The effect of tinctures on mycelium growth and spore germination of the pathogen was tested. Tinctures at 20% concentration promoted reduction of disease severity. A reduction of 80% in the diameter of leaf lesions was observed for bitter melon tinctures and 75.3% for guava tinctures. In fruits, the reduction was 48.4% (bitter melon tinctures) and 43.3% (guava tinctures). Guava tinctures, starting at a concentration of 5%, inhibited 100% of mycelium growth of tangerine pathotype of A. alternata, while the use of bitter melon tinctures inhibited 100% of mycelium growth starting at a concentration of 10%. The greater sensitivity to tinctures observed when these were added to the culture medium when compared to inoculation in leaves and fruits may be explained due to the higher exposition of the pathogen to the active principle when the vegetal tinctures were added to the culture medium, than when tinctures were sprayed over the vegetal surface in fruits and leaves. The number of germinated spores decreases 76.7% and 82% when using tinctures from guava and bitter melon (20%). Tinctures from bitter melon and guava are potential tools for alternative management of the Alternaria brown spot in tangerine "Dancy".