Chenopodium quinoa - an Indian perspective

The area under the disease progress curve (AUDPC) is frequently used to combine multiple observations of disease progress into a single value. However, our analysis shows that this approach severely underestimates the effect of the first and last observation. To get a better estimate of disease progress, we have developed a new formula termed the area under the disease progress stairs (AUDPS). The AUDPS approach improves the estimation of disease progress by giving a weight closer to optimal to the first and last observations. Analysis of real data indicates that AUDPS outperforms AUDPC in most of the tested trials and may be less precise than AUDPC only when assessments in the first or last observations have a comparatively large variance. We propose using AUDPS and its standardized (sAUDPS) and relative (rAUDPS) forms when combining multiple observations from disease progress experiments into a single value.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-07-11-0216

The area under the disease progress stairs: calculation, advantage, and application.

Nanoparticles (NP) have great potential in agriculture. For example, micronutrients have poor mobility in plants and poor availability in neutral soils, yet they play pivotal roles in root health. We investigated whether foliar sprays of micronutrient NP could affect plant health in disease infested soils. In the greenhouse, NP of AlO, CuO, FeO, MnO, NiO, and ZnO were sprayed on tomatoes and grown in soilless medium infested with the Fusarium wilt fungus. NP of CuO, MnO, or ZnO reduced disease estimates [area-under-the-disease-progress-curve (AUDPC)] by 31%, 28%, or 28%, respectively, when compared to untreated controls. When NP of CuO, MnO, or ZnO, their bulked equivalents, or their sulfate salts were compared to untreated eggplants and held in the greenhouse in soilless medium infested with the Verticillium wilt fungus, NP of CuO increased fresh weights by 64%, reduced AUDPC values by 69%, and had 32% more Cu in the roots. These same amendments were sprayed onto the foliage of tomato and eggplant transplants and set in field plots in soil heavily infested with the Verticillium wilt fungus. Compared to untreated controls, yields of tomato were 33% or 31% greater with NP of CuO or the bulked MnO, respectively. NP of CuO or ZnSO4 increased eggplant yields by 34% or 41% when compared to controls, respectively. In vitro studies found NP of CuO were not inhibitory to the Fusarium wilt fungus, suggesting host defense was being manipulated.

The use of metallic oxide nanoparticles to enhance growth of tomatoes and eggplants in disease infested soil or soilless medium

Plant pathogenic bacteria cause high crop and economic losses to human societies1-3. Infections by such pathogens are challenging to control as they often arise through complex interactions between plants, pathogens and the plant microbiome4,5. Experimental studies of this natural ecosystem at the microbiome-wide scale are rare, and consequently we have a poor understanding of how the taxonomic and functional microbiome composition and the resulting ecological interactions affect pathogen growth and disease outbreak. Here, we combine DNA-based soil microbiome analysis with in vitro and in planta bioassays to show that competition for iron via secreted siderophore molecules is a good predictor of microbe-pathogen interactions and plant protection. We examined the ability of 2,150 individual bacterial members of 80 rhizosphere microbiomes, covering all major phylogenetic lineages, to suppress the bacterium Ralstonia solanacearum, a global phytopathogen capable of infecting various crops6,7. We found that secreted siderophores altered microbiome-pathogen interactions from complete pathogen suppression to strong facilitation. Rhizosphere microbiome members with growth-inhibitory siderophores could often suppress the pathogen in vitro as well as in natural and greenhouse soils, and protect tomato plants from infection. Conversely, rhizosphere microbiome members with growth-promotive siderophores were often inferior in competition and facilitated plant infection by the pathogen. Because siderophores are a chemically diverse group of molecules, with each siderophore type relying on a compatible receptor for iron uptake8-12, our results suggest that pathogen-suppressive microbiome members produce siderophores that the pathogen cannot use. Our study establishes a causal mechanistic link between microbiome-level competition for iron and plant protection and opens promising avenues to use siderophore-mediated interactions as a tool for microbiome engineering and pathogen control.

Competition for iron drives phytopathogen control by natural rhizosphere microbiomes.

Transcriptome of silicon-induced resistance against Ralstonia solanacearum in the silicon non-accumulator tomato implicates priming effect

Calculation of the area under the disease-progress curve (AUDPC) as a measure of quantitative disease resistance entails repeated disease assessments. For typical sigmoid disease-progress curves, repeated assessments may be unnecessary. A mathematical procedure is derived for estimating the AUDPC from two data points. A field trial with ten cultivars with and without the gene Yr18 for resistance to stripe rust were inoculated with two pathotypes of Puccinia striiformis (from the cultivars Karamu and Oroua) and assessed for the percentage leaf area infected seven or eight times during the growing season. The AUDPCs were calculated directly from data and estimated from the described equation. Calculated values were plotted and ranked against estimated values, and excellent correspondence was obtained (Spearman’s Rank Correlation in the Karamu trial= 0.9879 and the Oroua trial=0.9515). Therefore, an estimation of the AUDPC from two data points provides an equivalent amount of information as from repeated assessments.

S. L. H. Viljanen-Rollinson

Papers

The use of the area under the disease-progress curve (AUDPC) to assess quantitative disease resistance in crop cultivars