Conversion of sheath blight susceptible indica and japonica rice cultivars into moderately resistant through expression of antifungal ß-1,3-glucanase transgene from Trichoderma spp.

Rice is an important food crop for three billion people worldwide. The crop is vulnerable to several diseases. Sheath blight caused by fungal pathogen Rhizoctonia solani is a significant threat to rice cultivation accounting for up to 50% yield losses. The pathogen penetrates leaf blades and sheaths, leading to plant necrosis; and major disease resistance gene against the pathogen is not available. This study describes development of sheath blight resistant transgenic indica and japonica rice cultivars through introduction of antifungal ß-1,3-glucanase transgene cloned from Trichoderma. The transgene integration and expression in transformed T0 rice plants was examined by PCR, RT-PCR, qRT-PCR demonstrating up to 5-fold higher expression as compared to non-transgenic plants. The bioassay of T0, T1 and homozygous T2 progeny plants with virulent R. solani isolate revealed that plants carrying high level of ß-1,3-glucanase expression displayed moderately resistant reaction to the pathogen. The optical micrographs of leaf sheath cells from moderately resistant plant after pathogen inoculation displayed presence of a few hyphae with sparse branching; on the contrary, pathogen hyphae in susceptible non-transgenic plant cells were present in abundance with profuse hyphal branching and forming prominent infection cushions. The disease severity in T2 progeny plants was significantly less as compared to non-transgenic plants confirming role of ß-1,3-glucanase in imparting resistance.

Interaction of TiO2 nanoparticles with soil: Effect on microbiological and chemical traits.

Titanium dioxide (TiO2) nanoparticles (NPs) are the most widely used nanomaterials and their expanding use raises concerns about their impacts on soil ecosystems and functioning. The present study evaluates the potential impacts of TiO2 NPs applied at low doses (0, 1.0, 2.5, 5.0, 10.0 and 20.0 mg L-1) on soil chemical properties including the macro and micronutrient contents, microbial population and enzyme activities in rhizosphere soil of mung bean crop at different time intervals (7, 14, 28 and 56 days). A quantitative RT-PCR study was also performed to study the relative change in the gene expression of ammonia oxidizer and nitrogen fixers upon TiO2 NP supplementation. An increase in soil nutrient content viz., available N, P, Cu, Fe, Mn, nitrate-N and ammonical-N was observed with NP application except available K and Zn content. The TiO2 NPs stimulated the growth of soil microflora at low concentrations while an inhibitory effect was recorded at high concentrations. The soil fungi and actinobacteria emerged as the most sensitive groups of soil microbes towards TiO2 NP exposure exhibiting detrimental impacts on their growth at all concentrations. Similarly, the soil enzyme activities enhanced till TiO2 NPs (10.0 mg L-1) which was followed by decrease at higher concentrations. The qRT-PCR study showed that the ammonia oxidizers were more affected by TiO2 NPs application than nitrogen fixers. These findings suggest that TiO2 NPs can be used as stimulators of soil nutrients and soil microbial dynamics at low concentrations.