Abstract
Alternaria rot, caused by Alternaria alternata, is one of the most destructive diseases of pitahaya (Hylocereus spp.). We investigated the effect of the essential oil of Baccharis dracunculifolia (Asteraceae) (EOB) in the control of A. alternata. Two studies were performed in Petri dishes containing potato dextrose agar medium amended with concentrations of the EOB ranging from 5 to 1,000 µg mL-1 (first study) and from 30 to 2,000 µg mL-1. The diameter of the fungal colony was recorded daily. These data were used to calculate the the area under the mycelial growth progress curve (AUMGPC) and mycelial growth index (MGI). In the third study, the control of Alternaria rot in pitahaya fruits by EOB was investigated by adding the EOB into an edible coat based on cassava starch and sorbitol which was prepared in Tween 20. Three treatments, containing EOB at 500, 1,000 or 2,000 µg mL-1, were assessed. Two additional treatments, one containing water and another containing only the edible coating served as controls. Pitahaya fruits were immersed in those solutions for 10 min, allowed to dry and inoculated with A. alternata 48 h later. The EOB was found to inhibit the mycelial growth and a negative and quadratic model best described the relationship of the EOB concentrations with MGI and AUMGPC. Results from the experiment performed with pitahaya fruits showed that Alternaria rot was decreased with increasing EOB concentrations. Therefore, EOB is a promising and ecofriendly method that may be included in the management of Alternaria rot in pitahya.
Highlights
Pitahaya (Hylocereus undatus Haw.), known as dragon fruit, is a member of the Cactaceae family that is native to the tropical forest regions of Mexico and Central and South Amercia (Mizrahi et al, 1997)
Low concentrations (< 70 μg mL-1; T2 and T3) of the essential oil of B. dracunculifolia (EOB) almost did not inhibit the mycelial growth of the fungus, whereas a small inhibition was observed in concentrations between 160 and 373 μg mL-1 (T4 and T5)
The lowest values of area under the mycelial growth progress curve (AUMGPC) and mycelial growth index (MGI) were obtained at the EOB concentrations of 950 and 500 μg mL-1, respectively
Summary
Pitahaya (Hylocereus undatus Haw.), known as dragon fruit, is a member of the Cactaceae family that is native to the tropical forest regions of Mexico and Central and South Amercia (Mizrahi et al, 1997). The fruit has received great attention in the recent years due to its attractive color and economic value as food products, but especially for its health properties (Kim et al, 2011). Since pitahaya is a newly cultivated crop, postharvest studies have been limited. Fruits keep quality around six to eight days after harvesting, whereas an inadequate handling and environment results in quicker deterioration, decreasing shelf life and compromising its commercial value (Castro et al, 2017; Chaemsanit et al, 2018). Given the lack of studies, research-based information to develop postharvest techniques that maintain fruit quality and increase fruit availability in the marketplace are needed (Freitas & Mitcham, 2013)
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