Evaluation of Biogenic Markers-Based Phenotyping for Resistance to Aphanomyces Root Rot in Field Pea

Biogenic volatile organic compounds (VOCs) emitted by plants can reveal information about plant adaptation, defense processes, and biological pathways. Thus, such VOC data may be utilized to capture phenotypic plant responses to the environment. In this study, the main objective was to evaluate the potential of biogenic compounds, including VOCs, to phenotype two pea cultivars, Ariel (susceptible) and Hampton (high levels of partial resistance) for resistance to Aphanomyces root rot disease. Plants were monitored non-destructively for VOC emission at three-time points (15, 20, and 30 days after inoculation, DAI) using dynamic headspace sampling with gas chromatography-flame ionization detection (GC-FID) system, as well as destructively at the end of the experiments, using solvent extraction and pyrolysis of both shoot and root tissues. A non-inoculated control (mock-inoculated with distilled water) was utilized to compare the plant responses within a cultivar. The common chemical peaks between control and inoculated samples of both cultivars (RTcm) were analyzed after normalizing the relative peak intensity of inoculated samples with those of control samples, prior to a comparison between cultivars. In addition, unique chemical peaks (RTuq) present in inoculated samples, but not in control samples were also identified and their relative peak intensities were compared. Among the released green leaf volatiles (RTcm), the normalized relative peak intensity of hexanal emission, at 20 DAI, was higher in Ariel than that of Hampton. In addition, several putative chemical peaks (both RTcm and RTuq), previously known as indicators for disease response, exhibited some differences in their emission rates between pea cultivars in at least one of the time points. The destructive sampling revealed that shoot samples produced more putative unique biomarkers (RTuq) than the root samples. Based on the differences in putative chemical peaks between cultivars, this initial study supports the concept of utilization of biogenic biomarker-based phenotyping in distinguishing levels of resistance in the evaluated pea cultivars. More research is needed to further this approach for phenotyping other plant cultivars. Upon validation, the VOC profile integrated with high-throughput VOC sensing techniques can serve as a novel mechanism for phenotyping disease responses in crops.