Abstract
Symbiotic effectiveness of rhizobitoxine (Rtx)-producing strains of Bradyrhizobium spp. in soybean (cultivar NRC-37/Ahilya-4) under limited soil moisture conditions was evaluated using phenomics tools such as infrared(IR) thermal and visible imaging. Red, green and blue (RGB) colour pixels were standardized to analyse a total of 1017 IR thermal and 692 visible images. Plants inoculated with the Rtx-producing strains B. elkanii USDA-61 and USDA-94 and successive inoculation by B. diazoefficiens USDA-110 resulted in cooler canopy temperatures and increased canopy greenness. The results of the image analysis of plants inoculated with Rtx-producing strains were correlated with effective nodulation, improved photosynthesis, plant nitrogen status and yield parameters. Principal component analysis (PCA) revealed the reliability of the phenomics approach over conventional destructive approaches in assessing the symbiotic effectiveness of Bradyrhizobium strains in soybean plants under watered (87.41–89.96%) and water-stressed (90.54–94.21%) conditions. Multivariate cluster analysis (MCA) revealed two distinct clusters denoting effective (Rtx) and ineffective (non-Rtx) Bradyrhizobium inoculation treatments in soybean. Furthermore, correlation analysis showed that this phenotyping approach is a dependable alternative for screening drought tolerant genotypes or drought resilience symbiosis. This is the first report on the application of non-invasive phenomics techniques, particularly RGB-based image analysis, in assessing plant-microbe symbiotic interactions to impart abiotic stress tolerance.
Highlights
The occurrence and magnitude of abiotic stresses might increase in the near future because of global climate change
It has been reported that symbiotic nitrogen fixation (SNF) is rapidly inhibited by water deprivation, as the deprivation causes changes in nodule morphology and metabolism[7]
The Rtx-producing traits of bradyrhizobial strains on symbiotic effectiveness and plant phenotypic responses are poorly understood under abiotic stresses, in nutrient-poor soils and low soil moisture stress conditions
Summary
The occurrence and magnitude of abiotic stresses might increase in the near future because of global climate change. The legume/Rhizobium symbiosis is destabilized by drought or low soil moisture, causing poor nodulation and premature nodule senescence[8, 9] These findings have unequivocally demonstrated that SNF is highly sensitive to water availability in the root environment. The Rtx-producing traits of bradyrhizobial strains on symbiotic effectiveness and plant phenotypic responses are poorly understood under abiotic stresses, in nutrient-poor soils and low soil moisture stress conditions. The understanding and assessment of plant responses to these symbiotic interactions on both plant physiology (plant canopy features, plant water status and photosynthetic efficiency) and biochemical metabolism and their impact due to improved root nodulation and nitrogen fixation through advanced phenomics approaches under low soil moisture stress conditions/moderate drought stress are poor[24]
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