(E)-2-Hexenal Can Stimulate Botrytis cinerea Growth in vitro and on Strawberries in vivo during Storage

Abstract

<jats:p>Some plant-derived natural volatile compounds exhibit antifungal properties and may offer an opportunity to control the causes of postharvest spoilage without affecting quality of, or leaving a residue on, fresh produce. The natural wound volatile (<jats:italic>E</jats:italic>)-2-hexenal has exhibited significant antifungal activity in earlier studies, but effects on spore germination and mycelial growth have not been separated, nor has the inhibitory mode of action been determined. To determine the efficacy of (<jats:italic>E</jats:italic>)-2-hexenal for control of <jats:italic>Botrytis cinerea</jats:italic> Pers. ex Fr. spore germination and mycelial growth, and to examine the mode of action, in vitro and in vivo studies were performed. Under in vitro bioassay conditions, spore germination was more sensitive to the compound than was mycelial growth. Vapor from 10.3 μmol of (<jats:italic>E</jats:italic>)-2-hexenal in a 120-mL petri dish completely inhibited spore germination. However, 85.6 μmol of (<jats:italic>E</jats:italic>)-2-hexenal was required to completely inhibit mycelial growth. Lower concentrations of the compound (5.4 and 10.3 μmol) significantly stimulated mycelial growth, especially when the volatile was added 2 days following inoculation. Mycelial growth did not occur as long as the vapor-phase concentration was 0.48 μmol·L<jats:sup>-1</jats:sup> or greater. Light microscopy analysis indicated that a high concentration of volatile compound dehydrated fungal hyphae and disrupted their cell walls and membranes. Exposure of B. <jats:italic>cinerea</jats:italic>-inoculated and non-inoculated strawberry (<jats:italic>Fragaria ×ananassa</jats:italic> Duch.) fruit in 1.1-L low-density polyethylene film-wrapped containers to vapor of (<jats:italic>E</jats:italic>)-2-hexenal at 85.6 or 856 μmol (10 or 100 mL, respectively) per container for durations of 1, 4, or 7 days during 7 days of storage at 2 °C promoted the incidence of <jats:italic>B. cinerea</jats:italic> during subsequent shelf storage at 20 to 22 °C. Loss of fruit fresh mass and fruit firmness during storage at 22 °C was increased by (<jats:italic>E</jats:italic>)-2-hexenal treatment, but fruit total soluble solids, pH, titratable acidity, and color (L, C, and H values) were not affected. Thus, maintenance of a high vapor-phasel level of (<jats:italic>E</jats:italic>)-hexenal, perhaps &gt;0.48 μmol·L<jats:sup>-1</jats:sup>, may be necessary to inhibit mycelial growth and avoid enhancing postharvest mold problems, while significantly higher levels may be necessary to completely eliminate the pathogen.</jats:p>

Control of Penicillium expansum by plant volatile compounds

“…The efficacy of some compounds depended on fungal growth stage: P. expansum conidial germination was more sensitive to trans ‐2‐hexenal concentration than mycelial growth, while the opposite was found for the phenols, carvacrol and eugenol, and for the aldehydes, trans ‐cinnamaldehyde and citral. These findings are in agreement with those reported by Fallik et al . (1998) for trans ‐2‐hexenal against B. cinerea.…”

Fungicidal Activity of Plant Volatile Compounds for Controlling Monilinia laxa in Stone Fruit

“…M. laxa mycelial growth was more sensitive to the phenols carvacrol and eugenol and to the aromatic aldehydes trans-cinnamaldehyde and panisaldehyde than was conidial germination, whereas the opposite was found for the aliphatic aldehydes trans-2-hexenal and hexanal and the ketone 2-nonanone. A greater sensitivity of conidia than mycelia to trans-2-hexenal vapors also was found in B. cinerea (16). Bioassay results confirmed the antifungal activity against M. laxa by trans-2-hexenal vapor treatment (20 µl/liter in peach, nectarine, and plum and 10 µl/liter in apricot), with efficacy varying from 42.6 to 97.1%.…”

“…Previous studies on B. cinerea with trans-2-hexenal (16) and on Cladosporium herbarum with carvacrol (1) showed that these compounds cause severe damage to fungal membranes and cell walls, which leads to morphological deformations and collapse and deterioration of conidia or hyphae. The fungicidal activity of trans-2-hexenal and citral aldehydes may be ascribed to the high electrophilic properties of the carbonyl group adjacent to the double bond that make these compounds particularly reactive with nucleophiles, such as protein sulfhydryl and amino groups of the pathogen (2).…”

Postharvest treatment with trans-2-hexenal induced resistance against Botrytis cinerea in tomato fruit

“…Trans-2-hexenal effectively reduced blue mold infections and patulin content in "Conference" pears and apples (Neri et al 2006), and the shelf life of apple slices is extended by inhibiting Pichia subpelliculosa infection (Corbo et al 2000). The concentration dependent inhibition of growth of B. cinerea have been observed that the inhibition was evident with 1 μM or higher of trans-2-hexenal (Fallik et al 1998).…”