Effective control of wheat stem rot by Chaetomium globosum

Chaetomium is an important group of plant pathogenic fungi, which is one of the most abundant groups of ascomycetes, and can effectively degrade cellulose and organic matter and antagonize a variety of microorganisms. In this genus, there are C. globosum, C. cupreum and C. cochliodes, etc. The most studied ones are C. globosum, C. cupreum and C. cochliodes. Among them, C. globosum belongs to Ascomycota, Sordariomycetes, Sordariales, Chaetomiaceae, Trichoderma. The ascomycete shell is spherical, ovate or obovate, with an apical orifice; the ascomycete shell is attached with bristles, unbranched, irregular and loosely curled; the ascomycetes are clavate or slightly pike-like and easily dissipated; the ascomycete shell contains ascospores, and each ascospores contains 8 ascospores; the ascospores are brown, lemon shaped and are 9-12 µm in length, 8-10 µm in width, and 6-8 µm in thickness.

Trichoderma reesei is a common endophytic fungus, which is widely distributed in air, soil and other natural environments, and has multiple functions such as producing antimicrobial active substances, promoting plant growth, inducing plant resistance, competing for ecological niches and nutrients, and reparasitizing. Trichoderma globigii has a good effect of biocontrol on a variety of plant diseases, can decompose and utilize plant cellulose, and produces a large number of biologically active secondary metabolites, which has a greater potential for application in the fields of agriculture, medicine and industry.

The researchers identified the strain 12XP1-2-3 as Trichoderma bulbifaciens through the observation of its culture morphology and microscopic characteristics, combined with the phylogenetic analysis of ITS and tef1 gene sequences. Plate confrontation revealed that the strain was able to significantly inhibit the growth of Fusarium pseudoharzianum mycelium, with an inhibition rate of 65.9%; it was also able to inhibit a variety of Fusarium pathogenic fungi such as Fusarium laminarum, Fusarium graminearum and other Fusarium species. In addition, the spore germination rate of Fusarium globosum after treatment with sterile fermentation broth also decreased significantly, the germination rate was only 42.4%, and the inhibition rate of spore germination reached 55.3%; the mycelial growth of the pathogenic fungi on the PDA plate added with sterile fermentation broth decreased significantly.

Fig. 1 Inhibitory effect of Trichoderma globulus 12XP1-2-3 on Fusarium pseudoharzianum.

Using Trichoderma globulus 12XP1-2-3 spore suspension on wheat seed coating treatment, it was verified in pots and found that the isolation rates of root and stem inoculated strains were 75% and 80%, respectively, after wheat seedling emergence, which indicated that the strain had a high colonization efficiency on wheat plants. However, the spore suspension coating of the strain had no effect on the growth parameters of wheat, indicating that the growth-promoting effect of the strain was not obvious. Subsequently, 7 d after inoculation with Fusarium pseudoharzianum, the incidence of disease in wheat plants of the control treatment without Trichoderma globosum coating reached 66.6%, whereas most of the coated wheat plants did not show obvious symptoms of disease, with only 3.9% of the diseased plants. After 35 d of pathogen inoculation, the disease index of the treatment group was still significantly lower than that of the control group, and the disease prevention efficiency was 37.3%. Thus, pre-inoculation of wheat with Trichoderma globigii 12XP1-2-3 significantly delayed the emergence of disease symptoms and consistently reduced the disease index. In order to verify whether T. globulus inoculation could induce immune resistance in wheat, the expression of 21 genes related to disease resistance was examined at 7 and 21 d after inoculation, and it was found that the expression of most of the genes related to disease resistance was not activated during the pre-inoculation period, but most of the disease resistance genes were significantly up-regulated at 21 d after inoculation.

Fig. 2 Effect of Trichoderma globulus 12XP1-2-3 coating on wheat stem basal rot control

Through the field trials in three locations in three years, it was proved that the wheat group inoculated with Trichoderma globigii performed well in the field trials in various growth traits throughout the wheat growth period. Although the plant height, root length, fresh weight and dry weight of wheat plants at different growth periods were not significantly different from those of the blank control and phenyl ether metronidazole-coated treatments, the chlorophyll content of wheat flag leaves inoculated with Trichoderma bulbifaciens was significantly higher than that of the other two treatments, which still proves the potential of utilizing the strain 12XP1-2-3 coating to promote the growth of wheat. Data from different years showed that the efficacy of wheat seed coated with spore suspensions of the strain and phenyl ether metronidazole against wheat stem basal rot also varied between years, locations and varieties. After field trials, it was found that the use of Trichoderma globulus 12XP1-2-3 on wheat seeds was able to significantly reduce the incidence of wheat stem rot and the yield loss caused by the disease in different years and different locations. Overall, the prevention effect on wheat stem rot after coating treatment was 25.0%-73.1%, and the basic prevention effect was close to that of phenyl ether metronidazole; and the yield increase of wheat after coating was significant, with a range of 3.2%-11.9%, which was significantly higher than that of chemical fungicide coating.

Trichoderma bulbifaciens has a good potential of biocontrol, but its research and development is still in the beginning stage, for the biocontrol mechanism and the development and application of the research should be further strengthened, in-depth investigation of its interactions with crops, pathogens and other environmental factors and the law, so that the best Trichoderma bulbifaciens biocontrol formulations can be created, and better play Trichoderma bulbifaciens in the application of plant disease prevention and promotion of the growth of the soil and straw degradation and other applications of the potential.

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