Purpureocillium lilacinum SBF054: Endophytic in Phaseolus vulgaris, Glycine max, and Helianthus annuus; Antagonistic to Rhizoctonia solani; and Virulent to Euschistus heros

Abstract

Microorganisms with multiple ecological functions can be a useful biotechnological resource in integrated pest- and disease-management programs. This work aimed to investigate the potential endophytic and virulent effects of a strain of Purpureocillium lilacinum on organic cultivation in Brazil. Specifically, the strain's ability to establish itself as an endophyte in common bean, soybean, and sunflower plants when inoculated via seed was evaluated. Furthermore, its antifungal activity against phytopathogens and its pathogenicity and virulence against insects of the order Lepidoptera, Coleoptera, and Hemiptera were evaluated. Furthermore, the strain was evaluated for its biochemical and physiological characteristics. For virulence bioassays, the experiments were conducted under a factorial scheme (2 × 3), with the following factors: (a) fungal inoculation and control without inoculum and (b) types of inocula (blastospores, aerial conidia, and metabolites). The treatments were sprayed on insect species at different stages of development. In summary, it was found that the SBF054 strain endophytically colonized the common bean, with partial recovery from the root tissues of soybean and sunflower plants, 30 days after inoculation; suppressed 86% of Rhizoctonia solani mycelial growth in an in vitro assay; and controlled eggs, nymphs, and Euschistus heros adults. These multifunctional abilities are mainly attributed to the strain's mechanisms of producing metabolites, such as organic acids, soluble nutrients, and hydrolytic enzymes.

Keywords: blastospores; endophytic colonization; entomopathogenic fungus; extracellular enzymes.

Figure 1

Morphological aspects of Purpureocillium lilacinum (SBF054) grown on a solid culture medium (potato dextrose agar): fungal colonies (scale bar: 1 cm) (A), hyphae and conidia (scale bar: 100 µm) (B), conidiophore (scale bar: 50 µm) (C). The propagules, blastospores (scale bar: 100 µm) (D), and microsclerotia (scale bar: 500 µm) (E) were produced under liquid fermentation after three days, and vegetative yeast cells (scale bar: 50 µm) (F) after seven days.

Figure 2

Clustermap of distance between strain SBF054 and the Purpureocillium lilacinum reference genome.

Figure 3

Fungal isolation in roots, stems, and leaves of young plants of Phaseolus vulgaris inoculated with P. lilacinum (scale bar: 1 cm) (A–C) and P. vulgaris, G. max, and H. annuus without fungal inoculation (E–G). Change in the quantity and arrangement of root hairs along the P. vulgaris root, with (D) or without inoculation with P. lilacinum (SBF054) (H). Scale bar: 1 mm in (D,H).

Figure 4

Percentage of fungal colonization (PCF) of P. lilacinum, strain SBF054, in agricultural crops.

Figure 5

Antifungal activity of P. lilacinum, strain SBF054 (A), against R. solani (A,B) in vitro. The phytopathogens Fusarium oxysporum (C) and Macrophomina phaseolina (D) were not affected. Scale bar: 1 cm.

Figure 6

Principal component analysis (PCA) of variables (A) and treatments (B), cluster analysis (C), and heatmap (D) as a function of the virulence of the fungus P. lilacinum SBF054 at different stages of development [EGG, NYMP, and ADULT] of E. heros, caterpillars of S. frugiperda [SPODOP], and A. grandis [ANTH] adults. The variables described were related to mortality [MORT] and mycosis [MYC].

Figure 7

Total mortality of eggs (A), nymphs (C,E) E. heros adults, and mortality due to mycosis in the respective stages of development (B,D,F) after 13 days of treatment with the different inocula P. lilacinum, strain SBF054. Medians followed by the same letters do not differ according to the Tukey test (p < 0.05).