Quantitative, image-based phenotyping methods provide insight into spatial and temporal dimensions of plant disease

Abstract

Plant disease symptoms exhibit complex spatial and temporal patterns that are challenging to quantify. Image-based phenotyping approaches enable multidimensional characterization of host-microbe interactions and are well suited to capture spatial and temporal data that are key to understanding disease progression. We applied image-based methods to investigate cassava bacterial blight, which is caused by the pathogen Xanthomonas axonopodis pv. manihotis (Xam). We generated Xam strains in which individual predicted type III effector (T3E) genes were mutated and applied multiple imaging approaches to investigate the role of these proteins in bacterial virulence. Specifically, we quantified bacterial populations, water-soaking disease symptoms, and pathogen spread from the site of inoculation over time for strains with mutations in avrBs2, xopX, and xopK as compared to wild-type Xam. ΔavrBs2 and ΔxopX both showed reduced growth in planta and delayed spread through the vasculature system of cassava. ΔavrBs2 exhibited reduced water-soaking symptoms at the site of inoculation. In contrast, ΔxopK exhibited enhanced induction of disease symptoms at the site of inoculation but reduced spread through the vasculature. Our results highlight the importance of adopting a multipronged approach to plant disease phenotyping to more fully understand the roles of T3Es in virulence. Finally, we demonstrate that the approaches used in this study can be extended to many host-microbe systems and increase the dimensions of phenotype that can be explored.

Time-resolved X-ray fluorescence analysis of element distribution and concentration in living plants: An example using manganese toxicity in cowpea leaves

“…4 and 7). Additionally, three-dimensional representation, as shown by Scheckel et al (2004) and Mutka et al (2016) and used in the present study with Mn (Fig. 6), permits evaluation of other elements also over time and space.…”

“…In this regard, ionomics is concerned with the examination of elements in plants with measurements normally conducted for bulk tissues (Salt et al, 2008). Spatial resolution of essential and nonessential elements within plant tissues is even more important in understanding their roles (Conn and Gilliham, 2010) and would be especially so when combined with temporal changes as shown recently in disease progression (Mutka et al, 2016). Indeed, such analyses on microscopic and temporal scales would have benefit across a wide range of fields within the plant sciences, including studies of element location concomitant with gene expression and physiological function, examining changes in the distribution of nutrients within plant tissues (including edible tissues that influence human nutrition), and understanding the movement and toxicity of contaminants.…”

Foundational and Translational Research Opportunities to Improve Plant Health

“…Investigations can be conducted using high-throughput, sophisticated phenomics approaches to track pathogen and pest interaction with hosts in controlled environmental chambers (Mutka et al 2016) as well as in field settings (Chakraborty and Newton 2011; Fahlgren, Gehan, and Baxter 2015). Nonetheless, individual pathosystems need foundational studies before impact will be realized because our current predictive ability on decadal scales is severely limited (Shaw and Osborne 2011).…”

Unraveling the molecules hidden in the gray shadows of quantitative disease resistance to pathogens

“…With these recent technologies, all of these parameters can be measured, even in the early plant phenological stages (Mutka and Bart, 2015). Wheat and sugarcane are some crops where these technologies have been used for detection and study of QDR (Mahlein et al, 2012;Bauriegel and Herppich, 2014;Mutka et al, 2016). Despite the fact that these techniques require a large number of previous evaluations in order to set the parameters for each disease, their potential in phenotyping plant disease is undeniable.…”