Crude Citric Acid of Trichoderma asperellum: Tomato Growth Promotor and Suppressor of Fusarium oxysporum f. sp. lycopersici

Abstract

Presently, the bioprocessing of agricultural residues to various bioactive compounds is of great concern, with the potential to be used as plant growth promoters and as a reductive of various diseases. Lycopersiconesculentum, one of the most consumed crops in the human diet, is attacked by Fusarium wilt disease, so the main aim is to biocontrol the pathogen. Several fungal species were isolated from decayed maize stover (MS). Trichodermaasperellum was chosen based on its organic acid productivity and was molecularly identified (GenBank accession number is MW195019). Citric acid (CA) was the major detected organic acid by HPLC. In vitro, CA of T.asperellum at 75% completely repressed the growth of Fusariumoxysporum f. sp. lycopersici (FOL). In vivo, soaking tomato seeds in CA enhanced the seed germination and vigor index. T. asperellum and/or its CA suppressed the wilt disease caused by FOL compared to control. There was a proportional increment of plant growth and yield, as well as improvements in the biochemical parameters (chlorophyll pigments, total phenolic contents and peroxidase, and polyphenol oxidase activities), suggesting targeting both the bioconversion of MS into CA and biological control of FOL.

Keywords: Fusarium wilt disease; biological control; molecular identification; organic acids.

Figure 1

Frequency percentages of different fungi on maize stover (MS) (mean ± SD); ¹ Frequency, % $=\frac{\mathrm{Number} \mathrm{of} \mathrm{infected} \mathrm{samples}}{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{tested} \mathrm{samples}}\times 100.$

Figure 2

Plate assay of the active cellulose-degrading Trichoderma sp. 15 with halo degradation zone around the fungal growth.

Figure 3

Screening of the cellulolytic fungal isolates for the biosynthesis of organic acids (mean ± SD).

Figure 4

Chromatogram of organic acids in the hydrolysate of the fermented MS Trichoderma sp. 15, as detected by HPLC. X-axis: Retention time (min), Y-axis: Observed peak area (mAU = milli-absorbance units.

Figure 5

Molecular phylogenetic tree of the partial sequence of the internal transcribed spacer, showing the position of Trichoderma strain sp. 15 (highlighted with yellow color) with respect to the closely related sequences in GenBank.

Figure 6

The growth of F. oxysporum was affected by different concentrations of CA of T. asperellum (mean ± SD). Different letter on a point indicates a significant difference at p ≤ 0.05.

Figure 7

Influence of CA on germination and vigor index of tomato seeds (mean ± SD). For each criterion, the column designated with a different letter indicates significant differences (p ≤ 0.05).

Figure 8

T. asperellum and its CA against wilt disease development of tomato seedlings after 40 days of sowing under greenhouse conditions (mean ± SD). For each criterion, the column superscripted by the same letter(s) is not significantly different at p ≤ 0.05. FOL = F. oxysporum f, sp. Lycopersici pathogen, CCA = chemical citric acid, Ts = T. asperellum spores, CA = Citric acid of Trichoderma.