The Effect of Endophytic Bacteria Bacillus subtilis and Salicylic Acid on Some Resistance and Quality Traits of Stored Solanum tuberosum L. Tubers Infected with Fusarium Dry Rot

Abstract

The effect of endophytic Bacillus subtilis (strains 10-4, 26D) and their compositions withsalicylic acid (SA) on some resistance and quality traits of stored potatoes infected with Fusariumdry rot were studied. The experiments were carried out on hydroponically grown Solanumtuberosum L. tubers that were infected before storage with Fusarium oxysporum and coated with B.subtilis 10-4, 26D with and without exogenous SA, and then stored for six months. It has been shownthat 10-4, 26D, 10-4 + SA, and 26D + SA reduced in different levels (up to 30-50%) the incidence ofF. oxysporum-caused dry rot (with the highest effect for 10-4 + SA). SA notably enhanced the positiveeffect of 10-4, while for 26D, such an effect was not observed. All of the tested treatments increasedamylase (AMY) and AMY inhibitors activity in infected tubers, while decreased Fusarium-inducedprotease activity (except in the case of 10-4 + SA, which promoted a slight increase) was revealed.10-4, 26D, and their compositions with SA decreased (in different degrees) the pathogen-causedlipid peroxidation, proline, and reducing sugars accumulation in potatoes after long-term storage.It was also discovered 10-4 and 26D, regardless of SA presence, decrease pathogen-inducedglycoalkaloids α-Solanine and α-Chaconine accumulation and preserved increased levels of starchand total dry matter in infected stored potatoes. The findings indicate endophytic B. subtilis and itscompositions with SA is a promising eco-friendly and bio-safe approach to cope with postharvestdecays of potato during long-term storage; however, when developing preparations-compositionsit should take into account the strain-dependent manner of B. subtilis action together with SA.

Keywords: Fusarium oxysporum; endophytic Bacillus subtilis; glycoalkaloids; hydrolytic enzymes; potatoes; quality; resistance; salicylic acid; storage.

Figure 1

Effect of B. subtilis 10-4 (104), B. subtilis 26D (26D), B. subtilis 10-4 + salicylic acid (SA) (104 + SA), and B. subtilis 26D + SA (26D + SA) on F. oxysporum development in potatoes during long-time storage for six months (A) and pictures of tubers stored six months after infestation with F. oxysporum and coated with B. subtilis strains 10-4, 26D, and their compositions with SA (B). For each treatment was used 30 mini-tubers in three replicates (± SEM). C(-)—negative control tubers infected before storage with F. oxysporum; 104—tubers infected with F. oxysporum and treated with B. subtilis 10-4; 104 + SA—tubers infected with F. oxysporum and treated with composition B. subtilis 10-4 + SA; 26D—tubers infected with F. oxysporum and treated with B. subtilis 26D; B. subtilis 26D + SA—tubers infected with F. oxysporum and treated with B. subtilis 26D + SA, SA—tubers infected before storage with F. oxysporum and treated with SA; C(+)—positive control tubers without infection and treatments.

Figure 2

In vitro antagonistic activity of tested B. subtilis 10-4 (Bs104) and B. subtilis 26D (Bs26D) against the phytopathogenic fungus F. oxysporum (F.o) (A) and microscopic visualizations of the F. oxysporum fungal growth and morphology in the absence and presence of B. subtilis 10-4 and 26D (B). The observation was done using a scanning electron microscope Biozero BZ-8100E (Keyence Co., Osaka, Japan). F.o—F. oxysporum; Bs—B. subtilis. Red arrows mean macroconidia produced by F. oxysporum.

Figure 3

Effect of endophytic bacteria B. subtilis 10-4 (104) and B. subtilis 26D (26D), individually and in compositions with SA (104 + SA, 26D + SA), on activities of hydrolytic enzymes protease (PRO) (A), amylase (AMY) (B) and inhibitors of protease (PRO inh) (C) and inhibitors of amylase (AMY inh) (D) in F. oxysporum-infected (F. oxysporum) and non-infected (Healthy) potato tubers during storage (time of storage six months). The bars are the means of three repetitions  ±  SEM. Different letters indicate a significant difference between the means at the probability level of p  < 0.05.

Figure 4

Effect of B. subtilis 10-4 (104), B. subtilis 26D (26D), B. subtilis 104 + salicylic acid (SA) (104 + SA), and B. subtilis 26D + SA (26D + SA) on the content of malondialdehyde (MDA) (A) and proline (B) in F. oxysporum-infected (F. oxysporum) and non-infected (Healthy) stored potato tubers (time of storage six months). The bars are the means of three repetitions ± SEM. Different letters indicate a significant difference between the means at the probability level of p < 0.05.

Figure 5

Changes in the contents of reducing sugars (RS) in non-infected (Healthy) and infected with the phytopathogenic fungus F. oxysporum (F. oxysporum) potato tubers under the influence of treatments with B. subtilis 10-4 (104), B. subtilis 10-4 + SA (104 + SA), B. subtilis 26D (26D) and B. subtilis 26D + SA (26D + SA) after six months storage. The bars are the means of three repetitions ± SEM. Different letters indicate a significant difference between the means at the probability level of p  <  0.05.

Figure 6

Changes in the contents of starch (A) and total dry matter (TDM) (B) in non-infected (Healthy) and infected with the phytopathogenic fungus F. oxysporum (F. oxysporum) potato tubers under the influence of treatments with B. subtilis 10-4 (104), B. subtilis 10-4 + SA (104 + SA), B. subtilis 26D (26D), and B. subtilis 26D + SA (26D + SA) after six months storage. The bars are the means of three repetitions ± SEM. Different letters indicate a significant difference between the means at the probability level of p <  0.05.

Figure 7

Effect of B. subtilis 10-4 (104), B. subtilis 10-4 + salicylic acid (SA) (104 + SA), B. subtilis 26D (26D), and B. subtilis 26D + SA (26D + SA) on the content of glycoalkaloids (GA) ɑ-Solanine (A), ɑ-Chaconine (B), total GA [TGA] (C), and the ratio of α-Chaconine (C) to α-Solanine (S) (C:S ratio) (D) in stored non-infected (Healthy) and infected with F. oxysporum (F. oxysporom) tubers after six months of storage. Data are presented as mean concentrations in milligrams glycoalkaloid per kilogram (mg/kg) fresh weight (FW) of potato tubers. The bars are the means of three repetitions ± SEM. Different letters indicate a significant difference between the means at the probability level of p  <  0.05. ** means the value is above the acceptable safe level (200 mg/kg) and * means the value is close to the critical level.