Native Killer Yeasts as Biocontrol Agents of Postharvest Fungal Diseases in Lemons

Abstract

Economic losses caused by postharvest diseases represent one of the main problems of the citrus industry worldwide. The major diseases affecting citrus are the "green mold" and "blue mold", caused by Penicillium digitatum and P. italicum, respectively. To control them, synthetic fungicides are the most commonly used method. However, often the emergence of resistant strains occurs and their use is becoming more restricted because of toxic effects and environmental pollution they generate, combined with trade barriers to international markets. The aim of this work was to isolate indigenous killer yeasts with antagonistic activity against fungal postharvest diseases in lemons, and to determine their control efficiency in in vitro and in vivo assays. Among 437 yeast isolates, 8.5% show to have a killer phenotype. According to molecular identification, based on the 26S rDNA D1/D2 domain sequences analysis, strains were identified belonging to the genera Saccharomyces, Wickerhamomyces, Kazachstania, Pichia, Candida and Clavispora. Killers were challenged with pathogenic molds and strains that caused the maximum in vitro inhibition of P. digitatum were selected for in vivo assays. Two strains of Pichia and one strain of Wickerhamomyces depicted a significant protection (p <0.05) from decay by P. digitatum in assays using wounded lemons. Thus, the native killer yeasts studied in this work showed to be an effective alternative for the biocontrol of postharvest fungal infections of lemons and could be promising agents for the development of commercial products for the biological control industry.

Evaluation of Native Wine Yeast as Biocontrol Agents Against Fungal Pathogens Related to Postharvest Diseases

“…Using inhibition zone diameter assay, in general all yeasts evaluated were capable to inhibit growth of fungus over 50 %, with exception of C. oeirensis YCPUC41. Perez et al [30], using the same method, evaluated the biocontrol activity of 13 yeasts belonging to the species Saccharomyces cerevisiae, Pichia fermentans, Kazachstania exigua and Candida catenulata against Penicillium digitatum, P.…”

Biocontrol ability of killer yeasts (Saccharomyces cerevisiae) isolated from wine against Colletotrichum gloeosporioides on grape

“…Lima et al identified 29 killer yeast strains isolated from different tropical fruits to control C. gloeosporioides . Perez et al isolated 437 yeast isolates and two strains of Pichia and one strain of Wickerhamomyces among them that have a killer phenotype depicted a significant protection from decay by Penicillium digitatum in wounded lemons. These biocontrol yeasts were isolated from plants.…”

“…Killer yeasts were found in many places such as wine fermentation process and exhibited different kinds of killer phenotype . The killer yeasts were able to kill other susceptible yeasts and some filamentous fungi through different mechanisms .…”

The ecology of killer yeasts: Interference competition in natural habitats

“…In laboratory cocultures under conditions permissive for toxin activity, killer strains are either considerably fitter than sensitive strains or they completely exclude sensitive strains (Bussey, Vernet, & Sdicu, 1988;McBride et al, 2008;Pieczynska et al, 2016;Wloch-Salamon, 2014). Killer yeasts can also inhibit or exclude filamentous fungi or bacteria under laboratory conditions (Morace et al, 1989;Perez et al, 2016;Polonelli & Morace, 1986;Stopiglia et al, 2014). Although killer toxins are effective at sensitive strain inhibition under laboratory conditions, ecologists do not fully understand the conditions under which they are effective in natural environments.…”