Gliotoxin produced by Trichoderma virens is inhibitory against various phytopathogenic fungi and bacteria. However, its stability in soil-ecosystem has not yet been well-defined. This study aimed to decipher its persistence and behaviour in growth media, irrigation water and soil ecosystems. Gliotoxin production was noticed at logarithmic growth phase and converted into bis-thiomethyl gliotoxin at late stationary growth phase of T. virens in acidic growth medium. But, no gliotoxin production was observed in neutral and alkaline growth medium. Gliotoxin was stable for several days in acidic water but degraded in alkaline water. Degradation of gliotoxin was more in unsterile soil than sterile soil and also that was higher under wet soil than dry soil. Degradation of gliotoxin was hastened by alkaline pH in wet soil but not in dry soil. Under unsterile soil conditions, high soil moisture increased the degradation of gliotoxin and the degradation of gliotoxin occurred quickly in alkaline soil (in 5 days) compared to acidic soil (in 10 days). Under sterile soil conditions, high soil moisture also enhanced the degradation of gliotoxin but level of degradation was less compared to unsterile conditions. Thus, gliotoxin stability is influenced mainly by the soil wetness, soil microbial community and pH conditions.
Phellorinia herculeana is an edible mushroom growing in nutritionally poor and desert soil. There has been little information available about its edaphic and culturing conditions for achieving the vigorous mycelial growth essential for its artificial cultivation, bioaugmentation and biodegradation in unfertile soil. Thus, the present study was conducted to assess its edaphic conditions and find a suitable culturing medium for obtaining maximum growth. It grows commonly in coastal soil with saline conditions, barren land soil unfit for cultivation, and desert soil. It forms a basidiocarp singly around xerophytic trees and annual plants and also in soil without vegetation. In addition to a well-developed pileus and stipe, it has a typical rhizoid that grows horizontally in soil. The rhizoid was thick at the base of the stipe and became thin into the mycelial strand. In our earlier study, we reported that its mycelial growth was very poor on nutrient-rich media containing simple sugar, for example, glucose. In the present study, we observed that cereal-grain-based agar media supported its mycelial growth and among the cereal-grain-based agar media, maize agar medium at the 5% level supported the maximum mycelial growth. Incorporation of glucose into the maize agar medium reduced its mycelial growth compared to its growth on maize agar medium without glucose. Its mycelial growth was at a maximum between 34 °C and 37 °C and at a pH between 7 and 8. Mass multiplication using sand-maize medium prepared at the ratio of 19:1 (sand: maize) supported the maximum mycelial growth. The results of this study would certainly pave a way for the scientific community to develop a protocol for its artificial cultivation and also for its mass multiplication, bioaugmentation and biodegradation in unfertile soil.
The false smut disease of rice incited by Ustilaginoidea virens is a major constraint on rice production. The main aim of the present study was to ascertain the false smut disease severity in both delta and non-delta districts of Tamil Nadu through survey and surveillance and assess the correlation between the disease severity and wind velocity for the past three years, 2019, 2020 and 2021. Moreover, the present study addressed the disease distribution pattern of false smut diseases under field conditions. The results obtained from survey results revealed that the maximum disease severity was recorded in Nagapattinam district (Nagapattinam block) with 27.45% and the minimum disease severity was recorded in the district Theni (Bodinayakanur block) with 8% in 2021. Similarly in 2019 and 2020 maximum disease severity was recorded in the following districts Thanjavur district (Orathanadu block) with 19.91% and Thanjavur district (Peravurani block) with 18.54% and the minimum disease severity was recorded in the following districts Madurai district (Madurai north block) with 4.78% and Madurai district (Usilampatti block) with 4.78% respectively. The obtained R2 values through regression analysis were 0.70, 0.79 and 0.76 in the following years, 2019, 2020 and 2021, respectively. Besides the relationship between the false smut disease development, the pattern wind direction was also assessed. By assessing the false smut disease distribution pattern under field conditions, more disease distribution was observed around the surrounding area of the paddy field as well as the diagonal path of the field which clearly revealed that wind direction influences the disease development.
Gliotoxin is a potent antibiotic showing antifungal activity against various phytopathogenic fungi. It is produced by Q strains of Trichoderma virens and gliotoxin non-producing strains of T. virens are designated as P strains. There is no detailed study on effect of gliotoxin on suppression of damping off of tomato caused by Pythium aphanidermatum and its phytotoxicity effect on tomato plants. Thus, the present study was carried out to assess the effect of gliotoxin on inhibition of mycelial growth of P. aphanidermatum, its phytotoxicity effect on tomato and its role on the suppression of damping off of tomato. Culture filtrates of Q strains of T. virens containing gliotoxin highly inhibited the mycelial growth of P. aphanidermatum compared to that of P strains of T. virens. Purified gliotoxin but not bis-thiomethyl gliotoxin effectively inhibited the mycelial growth of P. aphanidermatum. Tomato seeds treated with purified gliotoxin did not inhibit the germination of seeds, its root and shoot length even at higher concentration that is at 1000 ppm (fivefold inhibitory concentration against P. aphanidermatum). Foliar spray of gliotoxin on tomato plants did not show any phytotoxic effect at lower concentration but showed scorching effect at higher concentration. Seed treatment with gliotoxin producing Q strains of T. virens showed greater suppression of damping-off tomato compared to P strains of T. virens. This study clearly showed that gliotoxin producing T. virens could be used in suppression of damping-off disease incidence in tomato.
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