Trichoderma hamatum Increases Productivity, Glucosinolate Content and Antioxidant Potential of Different Leafy Brassica Vegetables

Abstract

Brassica crops include important vegetables known as "superfoods" due to the content of phytochemicals of great interest to human health, such as glucosinolates (GSLs) and antioxidant compounds. On the other hand, Trichoderma is a genus of filamentous fungi that includes several species described as biostimulants and/or biological control agents in agriculture. In a previous work, an endophytic strain of Trichoderma hamatum was isolated from kale roots (Brassica oleracea var. acephala), describing its ability to induce systemic resistance in its host plant. In the present work, some of the main leafy Brassica crops (kale, cabbage, leaf rape and turnip greens) have been root-inoculated with T. hamatum, having the aim to verify the possible capacity of the fungus as a biostimulant in productivity as well as the foliar content of GSLs and its antioxidant potential, in order to improve these "superfoods". The results reported, for the first time, an increase in the productivity of kale (55%), cabbage (36%) and turnip greens (46%) by T. hamatum root inoculation. Furthermore, fungal inoculation reported a significant increase in the content of total GSLs in cabbage and turnip greens, mainly of the GSLs sinigrin and gluconapin, respectively, along with an increase in their antioxidant capacity. Therefore, T. hamatum could be a good agricultural biostimulant in leafy Brassica crops, increasing the content of GSLs and antioxidant potential of great food and health interest.

Keywords: Trichoderma; aliphatic glucosinolates; cabbage; phenols; turnip greens.

Figure 1

Mean of fresh (a) and dry weight (b) of kale (Boa), cabbage (Boc), leafy rape (Bn) and leafy turnip (Br) grown in greenhouse conditions. Plants without inoculation and inoculated with T. hamatum (+Th) were collected at 8 weeks old and measured their fresh and dry weight of the aerial part. Data are the mean of 10 plants for each crop and condition with the corresponding standard deviation. Student’s t-test was performed between uninoculated and Trichoderma-inoculated plants. Asterisks denote significant differences at p ≤ 0.05 (*).

Figure 2

GSLs contents in leaves from kale (Boa) (a), cabbage (Boc) (b), leafy rape (Bn) (c) and leafy turnip (Br) (d) without inoculation and inoculated with T. hamatum (+Th). GIB: glucoiberin, SIN: sinigrin, PRO: progoitrin, ALY: glucoalyssin, GNA: gluconapin, GBS: glucobrassicin, MeOH: metoxy-glucobrassicin, NeoGBS: neoglucobrassicin, GNT: gluconasturtiin. Data are the mean of 10 plants for each crop and condition with the corresponding standard deviation. Student’s t-test was performed between uninoculated and Trichoderma-inoculated plants for each GSL. Asterisks denote significant differences at p ≤ 0.05 (*).

Figure 3

Antioxidant activity (ABTS⁺) (a) and phenolic content (Folin reagent) (b) in leaves from kale (Boa), cabbage (Boc), leafy rape (Bn) and leafy turnip (Br) without inoculation and inoculated with T. hamatum (+Th). Data are the mean of 10 plants for each crop and condition with the corresponding standard deviation. Student’s t-test was performed. Asterisks denote significant differences at p ≤ 0.05 (*).

Figure 4

Measurements of Brassica-root colonization by Trichoderma by qPCR in kale (Boa), cabbage (Boc), leafy rape (Bn) and leafy turnip (Br). Values are the proportion of fungal DNA vs. plant DNA means of three root pools (three plants each one) with the corresponding standard deviations. One-way analysis of variance (ANOVA) was performed, followed by the Tukey’s test. No significant differences (p < 0.05) were found.