(E)-2-HEXENAL CAN STIMULATE BOTRYTIS-CINEREA GROWTH IN-VITRO AND ON STRAWBERRIES IN-VIVO DURING STORAGE

Some plant-derived natural volatile compounds exhibit antifungal prope rties and may offer an opportunity to control the causes of postharves t spoilage without affecting quality of, or leaving a residue on, fres h produce. The natural wound volatile (E)-2-hexenal has exhibited sign ificant antifungal activity in earlier studies, but effects on spore g ermination and mycelial growth have not been separated, nor has the in hibitory mode of action been determined, To determine the efficacy of (E)-2-hexenal for control of Botrytis cinerea Pers, ex Fr, spore germi nation and mycelial growth, and to examine the mode of action, in vitr o and in vivo studies were performed. Under in vitro bioassay conditio ns, spore germination was more sensitive to the compound than was myce lial growth, Vapor from 10.3 mu mol of (E)-2hexenal in a 120-mL petri dish completely inhibited spore germination. However, 85.6 mu mol of Q -2-hexenal was required to completely inhibit mycelial growth. Lower c oncentrations of the compound (5.4 and 10.3 mu mol) significantly stim ulated mycelial growth, especially when the volatile was added 2 days following inoculation. Mycelial growth did not occur as long as the va por-phase concentration was 0.48 mu mol.L-1 or greater. Light microsco py analysis indicated that a high concentration of volatile compound d ehydrated fungal hyphae and disrupted their cell walls and membranes. Exposure of B. cinerea-inoculated and non-inoculated strawberry (Fraga ria xananassa Duch,) fruit in 1.1-L low-density polyethylene film-wrap ped containers to vapor of (E)-2hexenal at 85.6 or 856 mu mol (10 or 1 00 mt, respectively) per container for durations of 1, 4, or 7 days du ring 7 days of storage at 2 OC promoted the incidence of B. cinerea du ring subsequent shelf storage at 20 to 22 OC. Loss of fruit fresh mass and fruit firmness during storage at 22 OC was increased by (E)-2-hex enal 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-phase level of (E)-hexenal, perhaps >0.48 mu mol.L-1, may be necessary to inhibit mycelial growth and avoid enhancing postha rvest mold problems, while significantly higher levels may be necessar y to completely eliminate the pathogen.