Plant, pathogen and biocontrol agent interaction effects on bioactive compounds and antioxidant activity in garlic

Highlights

• Yeasts and bacteria can reduce the size of the lesions caused by S. Sclerotiorum.

• Plant, pathogen and biocontrol agent interaction can activate plant defense.

• Thiosulfinates content in garlic was higher in the presence of microorganisms.

• Plant-microbe interaction can increase garlic antioxidant activity.

Abstract

The purpose of this study was to evaluate the effect of biocontrol agents against Sclerotinia sclerotiorum in garlic phenols and thiosulfinates content, and antioxidant activity. The results showed that the lesion diameter is correlated with the bioactive compounds. Garlic cloves presented high phenols content and high reducing power in bigger lesions when treated with Saccharomyces cerevisiae. While in small lesions the thiosulfinates content and the ORAC were high when treated with Bacillus pumilus. The use of bioagents has the potential to increase plant production of bioactive compounds, as well as its antioxidant activity, in addition to promoting pathogen control.

Introduction

Garlic (Allium sativum L.) is an important representative of Alliaceae family that has been cultivated for a long time and whose pharmacological properties are related to the presence of secondary metabolites, such as phenolic and organosulfur compounds. Organosulfur compounds in garlic are known to be responsible for their strong characteristic odor, highlighting allicin, a thiosulfinate responsible for most of the biological activities of garlic, like antibiotic, antiviral and antifungal properties [1,2], and phenolic compounds, which are strongly related to antioxidant activity [3]. Garlic planting has been done earlier to avoid white rot disease (Sclerotium cepivorum), but this management can favor the development other pathogens such as white mold infestation (Sclerotinia sclerotiorum), and its occurrence in garlic crop is already reported in the south and southeast regions of Brazil (data not published) [4]. S. sclerotiorum can infect more than 500 species worldwide and is considered the most devastating and cosmopolitan plant pathogen, garlic being one of its host species [[5], [6], [7], [8]].

During the infection by pathogens, one of the plant's forms of defense is linked to an oxidative burst that triggers secondary responses and produces reactive oxygen species (ROS) [9]. To prevent ROS damage to cells, plants can produce enzymatic and non-enzymatic antioxidants [10,11]. Thiosulfinates and phenolic compounds are associated with the protection of garlic, being related to its defense response, acting as non-enzymatic antioxidants and like antifungal metabolites [2,12,13].

Pathogenesis can influence the production of secondary metabolites in plants, and the use of beneficial microorganisms to induce plant resistance also shares this principle, when the plant starts to produce metabolites that can protect it from pathogens, turning it resistant [14]. Therefore, when using bioagents to control S. sclerotiorum in garlic, it is desirable to know the effects of this interaction on the secondary metabolites content of the plant and its antioxidant activity.

Yeasts and Bacillus spp. were tested by Cavalcanti et al. [4] for prevention of S. sclerotiorum infection in garlic, showing that these potential biocontrol agents produce antifungal metabolites that inhibit the pathogen development. In view to expand on the research, this work aimed to evaluate the effect of interactions between plant, pathogen and antagonistic microorganisms on bioactive compounds in garlic and its antioxidant activity.