Insights into the Role of Streptomyces hydrogenans as the Plant Growth Promoter, Photosynthetic Pigment Enhancer and Biocontrol Agent against Meloidogyne incognita in Solanum lycopersicum Seedlings

Abstract

Root-knot nematodes (RKN), Meloidogyne sp. hinders functioning of crops and causes global losses in terms of productivity and yield. Meloidogyne sp. are microscopic, obligatory endoparasites with ubiquitous distribution in different parts of the world. Taking into consideration these aspects, the present study was conducted to explore nematicidal activity of the Streptomyces hydrogenans strain DH-16 against M. incognita to regulate its pathogenicity in plants. In-vitro experimentation revealed that pretreated seeds with solvent and culture supernatant lowered root galls in infested plants and promoted growth of Solanum lycopersicum seedlings, revealed through the morphological analysis. Additionally, antioxidative defense responses were induced with microbes. However, oxidative stress markers were considerably reduced after microbial inoculations. Apart from this, secondary metabolites were assessed and modulated in RKN infested plants on microbial supplementations. Confocal studies evaluated glutathione accumulation within root apices and its enhancement was directly proportional to defense responses. Therefore, the current study concluded the role of S. hydrogenans in stimulating antioxidant potential against RKN along with growth promoting aids. Thus, the outcome of the current study endorses that metabolites produced by S. hydrogenans can be used as safe biocontrol agents against M. incognita and also as plant growth promoting agents.

Keywords: Meloidogyne incognita; Streptomyces hydrogenans; antioxidants; confocal microscopy; oxidative damage; photosynthesis.

Figure 1

This figure depicts the change in morphometric parameters of tomato seedlings that were pretreated with a supernatant and extract. Different treatments are in order C (control), NI (nematode inoculated), S (supernatant), S + NI (supernatant + nematode inoculated), E (extract) and E + NI (extract + nematode inoculated).

Figure 2

Effect of the supernatant and extract containing biometabolites on the photosynthetic pigments (a) Chl “a”, (b) Chl “b”, (c) Total chl content and (d) Total Carotenoid content in 7-day-old L. esculetum nematode infected seedlings. Values are presented as means ± standard error (S.E.). F-values ** indicates significance at p ≤ 0.01 and * indicates significance at p ≤ 0.05. Various alphabets on the graphs indicate that the average mean values of treatments are significantly different according to Tukey’s multiple comparison test (C—Control, NI—Nematode, S—Supernatant, S + NI—Supernatant + Nematode inoculated, E—Extract, E + NI—Extract + Nematode inoculated).

Figure 2

Effect of the supernatant and extract containing biometabolites on the photosynthetic pigments (a) Chl “a”, (b) Chl “b”, (c) Total chl content and (d) Total Carotenoid content in 7-day-old L. esculetum nematode infected seedlings. Values are presented as means ± standard error (S.E.). F-values ** indicates significance at p ≤ 0.01 and * indicates significance at p ≤ 0.05. Various alphabets on the graphs indicate that the average mean values of treatments are significantly different according to Tukey’s multiple comparison test (C—Control, NI—Nematode, S—Supernatant, S + NI—Supernatant + Nematode inoculated, E—Extract, E + NI—Extract + Nematode inoculated).

Figure 3

Effect of the supernatant and extract containing biometabolites on the oxidative damage (a) MDA and (b) H₂O₂ content in 7-day-old S. lycopersicum nematode infected seedlings. Values are presented as means ± standard error (S.E.). F-values ** indicates significance at p ≤ 0.01 and * indicates significance at p ≤ 0.05. Various alphabets on the graphs indicate that the average mean values of different treatments are significantly different according to Tukey’s multiple comparison test (C—Control, NI—Nematode inoculated, S—Supernatant, S + NI—Supernatant + Nematode inoculated, E—Extract, E + NI—Extract + Nematode inoculated).

Figure 4

Effect of the supernatant and extract containing biometabolites on the non-enzymatic antioxidants (a) Tocopherol and (b) Glutathione content) in 7-day-old S. lycopersicum nematode infected seedlings. Values are presented as means ± standard error (S.E.). F-values ** indicates significance at p ≤ 0.01 and * indicates significance at p < 0.05. Various alphabets on the graphs indicate that the average mean values of different treatments are significantly different according to the Tukey’s multiple comparison test (C—Control, NI—Nematode inoculated, S—Supernatant, S + NI—Supernatant + Nematode inoculated, E—Extract, E + NI—Extract + Nematode inoculated).

Figure 5

Effect of the supernatant and extract containing biometabolites on the phenolic compounds: (a) anthocyanin and (b) flavonoid content in 7-day-old S. lycopersicum nematode infected seedlings. Values are presented as means ± standard error (S.E.). F-values ** indicates significance at p ≤ 0.01 and * indicates significance at p < 0.05. Various alphabets on the graphs indicate that the average mean values of different treatments are significantly different at p < 0.5 according to the Tukey’s multiple comparison test (C—Control, NI—Nematode inoculated, S—Supernatant, S + NI—Supernatant + Nematode inoculated, E—Extract, E + NI—Extract + Nematode inoculated).

Figure 6

Confocal micrographs showing images of glutathione tagging in differently treated control (C), nematode inoculates (NI), supernatant (S), supernatant (S + NI), extract (E) and extract + nematode inoculated (E + NI) S. lycopersicum roots 7 DAI by staining them with MCB.