Endophytic Fungi as Potential Biocontrol Agents against Sclerotium rolfsii Sacc.-The Causal Agent of Peanut White Stem Rot Disease.

Peanut stem white rot caused by Sclerotium rolfsii Sacc. is a soil-borne disease that is widely prevailing across peanut farms, leading to serious economic losses. Screening for biocontrol agents against this pathogen is urgent. In this research, 166 fungal isolates including 136 isolates of S. rolfsii and 30 isolates of antagonistic endophytic fungi were obtained from a total of 220 samples collected from peanut farms in Guilan province, Iran. After morphological and molecular identification, six superior endophytic isolates were finally selected for the in vitro and greenhouse trials, including four isolates from Trichoderma viride, Trichoderma virens, Penicillium decaturense, and Aspergillus flavus and two isolates from Penicillium rubens. Four methods of biocontrol were used during the in vitro phase, i.e., dual culture, volatile metabolites assay, non-volatile metabolites assay (culture extract), and slide culture. It was found that T. virens had the highest capability of suppressing the mycelial growth of S. rolfsii in the dual culture method (90.98%). As for the volatile metabolites assay, the most effective isolates in inhibiting the pathogen's mycelial growth were P. rubens (MN395854.1) and A. flavus (84.30% and 73.50% inhibition, respectively). In the non-volatile metabolites method, the isolates that performed the best in suppressing the mycelial growth of S. rolfsii were T. viride and P. rubens (MN395854.1) with 91.80% and 90.20% inhibitory effects, respectively. On the other hand, in the slide culture method, all isolates, except for T. virens and T. viride, successfully controlled the development of S. rolfsii hyphae. The greenhouse trials also supported the effectiveness of endophytic fungi in controlling the pathogen on the host plants. According to the results, T. viride, A. flavus, and P. rubens (MN395854.1) were 44%, 42%, and 38% effective in alleviating the disease incidence and severity. Moreover, the application of these antagonistic fungi in the greenhouse conditions increased the height, fresh weight, and dry weight of the Arachis hypogaea plants infected with the disease causal agent compared to the plants treated only with the pathogen. The results of the in vitro and greenhouse experiments revealed that the endophytic fungi occurring in the natural microbiota of peanut are capable of bio-controlling S. rolfsii, the causal agent of peanut stem white rot disease. These findings shed new insights into the possible resistance induction in A. hypogaea plants through biological protection.

Endophytic Fungi as Potential Biocontrol Agents against Rhizoctonia solani J.G. Kühn, the Causal Agent of Rice Sheath Blight Disease.

The rice sheath blight disease, caused by Rhizoctonia solani J.G. Kühn fungus, is a major disease of Oryza sativa L. occurring all over the world. Therefore, efforts need to be undertaken to limit the spread of this pathogen, preferably by using environmentally friendly methods. In the present study, 57 fungal isolates were recovered by surface sterilization technique from 120 rice samples collected from paddy fields in Guilan province, Iran. Biological characterizations of the isolated taxa were performed in vitro, in the dual culture, volatile metabolites, and slide culture methods. Among the studied isolates, Trichoderma virens (J. H. Miller, Giddens and A. A. Foster) Arx was most effective in inhibiting the mycelial growth of R. solani in the dual culture (44.16% inhibition level), while Aspergillus fumigatus Fresen and T. virens had a 62.50-68.75% inhibition efficiency by volatile metabolites. In the slide culture, all of the isolates, except for T. harzianum Rifai, were effective in inhibiting the hyphae growth of R. solani. Under greenhouse conditions, rice plants inoculated with these potential antagonistic fungi showed a reduction in disease severity by even 41.4% as in the case of T. virens. Moreover, phenotypic properties of rice, such as plant height, fresh weight, and dry weight were increased in the plants inoculated with all antagonistic fungi tested, compared to the infected plants, except for the fresh weight of plants inoculated with Curnularia lunata (Wakker) Boedijn. The present in vivo and in vitro studies revealed that T. virens and A. fumigatus are the most effective antagonists in rice sheath blight disease control and could be applied in agricultural practice.

Enhancement of 2,3-butanediol production by Klebsiella oxytoca PTCC 1402.

Optimal operating parameters of 2,3-Butanediol production using Klebsiella oxytoca under submerged culture conditions are determined by using Taguchi method. The effect of different factors including medium composition, pH, temperature, mixing intensity, and inoculum size on 2,3-butanediol production was analyzed using the Taguchi method in three levels. Based on these analyses the optimum concentrations of glucose, acetic acid, and succinic acid were found to be 6, 0.5, and 1.0 (% w/v), respectively. Furthermore, optimum values for temperature, inoculum size, pH, and the shaking speed were determined as 37°C, 8 (g/L), 6.1, and 150 rpm, respectively. The optimal combinations of factors obtained from the proposed DOE methodology was further validated by conducting fermentation experiments and the obtained results revealed an enhanced 2,3-Butanediol yield of 44%.