Biocontrol activity of Starmerella bacillaris yeast against blue mold disease on apple fruit and its effect on cider fermentation

Abstract

The reduction of chemical fungicides in agriculture has led to the use of microorganisms as biocontrol agents. Starmerella bacillaris is a non-Saccharomyces yeast associated with overripe and botrytized grape berries microbiota. Its use has been proposed for wine fermentation because of yeast fructophilic character and high glycerol production. Recently, S. bacillaris has been demonstrated to possess antifungal activity against Botrytis cinerea on the grape. Penicillium expansum is the pathogen responsible for the blue mold rot, the most important postharvest disease of apples. These fruits are the raw material of the cider, an alcoholic beverage commonly produced using S. cerevisiae starter cultures. In this study 14 S. bacillaris strains have been studied to evaluate their postharvest antifungal activity against P. expansum on apples. Moreover, the fermentation performances in apple juice of these non-Saccharomyces strains were tested, both in single-strain fermentation and in sequential fermentation, together with S. cerevisiae. Four S. bacillaris strains, able to significantly decrease blue mold rot symptoms and to increase glycerol content during fermentation have been selected to improve apple and cider quality.

Fig 1. Ability of S. bacillaris strains to reduce blue mold disease on apples.

a) Disease severity reduction (%). Data values with different letters differ significantly according to Dunn’s test (p<0.05). b) Lesion diameters (LD) measured on apple fruits inoculated with P. expansum (white bars) and on apple fruits treated with S. bacillaris one day before the inoculation with P. expansum (grey bars). Asterisks indicate significant differences (p<0.05) according to Student’s t-test. Lesion diameters were measured 7 days after P. expansum inoculation. During the experiment the apples were maintained at 25 °C, at high humidity.

Fig 2. Inhibition of P. expansum by live cells of S. bacillaris on Golden Delicious apples.

(a) Control on the left, strain PAS13 on the right (b) Control on the left, strain FRI700 on the right. Photographs were taken at day 7 of incubation at 25°C.

Fig 3. Ability of S. bacillaris strains PAS13, PAS92, FRI29 and FRI7100 to reduce blue mold disease on apples.

a) Disease severity reduction (%). Data values with different letters differ significantly according to Dunn’s test (p<0.05). b) Lesion diameters (LD) measured on apple fruits inoculated with Penicillium expansum (white bars) and on apple fruit treated with S. bacillaris one day before the inoculation with P. expansum (grey bars). Asterisks indicate significant differences (p<0.05) according to Student’s t-test. Lesion diameters were measured 7 days after P. expansum inoculation. During the experiment the apples were maintained at 25°C, at high humidity.

Fig 4. Population dynamics of S. bacillaris strains PAS13, PAS92, FRI29 and FRI7100 during 264 h of incubation inside apple wounds at 25 °C.

$─$ FRI729, $─$ FRI7100, $─$ PAS13, $─$ PAS92.