Furthering our understanding of the interaction of cereal rye allelochemicals with Pythium species and their impact on corn in the cereal rye-corn production system
Allelopathy is a complex process in which plants release chemical compounds that affect the growth and physiological processes of other plants. Allelochemicals also affect interactions between plants and microorganisms. With previous funding from the Iowa Nutrient Reduction Center (INRC), the researchers showed allelochemicals produced by the cover crop winter cereal rye (CR) reduced corn shoot and root growth in vitro and more severe seedling disease (root rot) was observed when corn was inoculated with some Pythium species.
Researchers will build on their previous research and further our understanding on the interaction of Pythium with rye and corn, thereby answering some fundamental questions regarding this system. This information could be used to identify management practices to help growers avoid corn yield losses following CR without limiting the numerous ecosystem services provided by CR.
The previous studies provided a brief insight into the interaction of allelopathy and Pythium species in the CR cover crop-corn production system, and how they may contribute to reduced yields. Pythium species infect both rye and corn. Moreover, Pythium species are attracted to both hosts by seed and root exudates. Researchers hypothesize that allelochemicals released from decomposing rye residue favor germination and/or activity of Pythium around the germinating corn seed facilitating increased infection of the seedling, which results in poor vigor and corn yield reductions in the CR-corn production system by favoring seedling pathogen-corn interactions and affecting early corn growth and development. This proof-of-concept study will provide further data regarding the interaction of allelopathic compounds and Pythium in a lab-based assay.
Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.
Key Research Questions:
(i) allelochemicals released from decomposing rye residue favor activity of Pythium in the corn spermosphere; and
(ii) activity of Pythium in the presence of allelochemicals produced by other cover crops would vary.
We used a microfluidic chip to test our hypotheses. We found that Pythium zoospores were attracted to exudates from both rye and corn equally compared to water, which was used as a negative control. We compared the effect of exudates from hairy vetch, crimson clover, mustard, and soybean with those from cereal rye. We observed more zoospores of Pythium lutarium attracted to exudates from cereal rye compared to exudates from hairy vetch, crimson clover, mustard, and soybean.
The findings from this initial research was used to leverage a second year of funding for further detailed research (INRC Award Number 2022-10) and publication of the two year research findings.
Related activities and accomplishments:
- 2 presentations
Researchers determined the effect of BOA on three species of Pythium using a plate assay. P. lutarium and P. oopapillum were tolerant to BOA at 0.125 and 0.25 mg/ml concentrations compared to the check plates (no BOA) when measured 24 hours after incubation at RT. In contrast, BOA inhibited P. torulosum, mycelial growth at both concentrations compared to the check plates.
When corn seedlings were grown on DV8++ media amended with BOA and inoculated with Pythium spp. (BOA + Pythium), coleoptile length and root length was reduced, and root rot severity increased with Pythium spp. Similarly, in plates amended from extracts prepared from cereal rye cv. Elbon, coleoptile length and radicle length were reduced, and root rot severity increased for all pathogens.
To understand the interaction of cereal rye allelochemicals with Pythium species to cause corn seedling disease, pure and crude extracts of rye and corn were obtained and tested against the infecting propagules of Pythium species (repeated in report below).
• The movement of zoospores of P. lutarium, P. oopapillum, and P. torulosum to rye and corn exudates were evaluated using a microfluidic chip developed in Greg Tylka’s lab (Beeman et al. 2016). We observed Pythium zoospores were attracted to both the rye exudates and the corn exudates (Figure 2) almost equally compared to water, a negative control.
• To better understand the chemotaxis response of Pythium zoospores towards rye allelochemicals, we collected exudates obtained from other plant species including hairy vetch, crimson clover, mustard, and soybean Only zoospores obtained from P. lutarium were used.
• Preliminary results suggest more zoospores were attracted to rye exudates compared to exudates obtained from other plants and the negative control. However, since the zoospores encysted while pipetting the treatment into the well, we need to optimize our protocol to confirm these data. • A draft of manuscript entitled “Effect of cereal rye allelochemicals on Pythium species and corn seedling growth and disease” has been prepared to submit to the Journal of PhytoFrontiers.
To understand the interaction of cereal rye allelochemical with Pythium species to cause corn seedling disease, pure and crude extracts of rye and corn were obtained and tested against various Pythium species. Pythium torulosum, P. lutarium, P. oopapillum, P. irregulare, and P. sylvaticum zoospores were induced following methods outlined by Lebreton et al. 2017. Among, the five species, only P. lutarium, P. torulosum, and P. oopapillum produced zoospores. Since P. irregulare, and P. sylvaticum belong to Clade B, they rarely produce zoospores.
The response of P. luatrium, P. oopapillum, and P. torulosum zoospores to rye and corn exudates was observed using a microfluidic chip developed in Greg Tylka’s lab (Beeman et al. 2016). Sterile water was included as a check. The number of zoospores that were attracted to rye exudates were compared with the number attracted to corn exudates and water. Pythium zoospores were more attracted to rye exudates than corn exudates or water.
Currently, researchers are in the process of identifying and quantifying BOA and MBOA (some of the most common allelochemicals produce by cereal rye) that come into contact with them in crude rye extracts using gas chromatography-mass spectrometry (GSMS). Research is focused on quantifying MBOA and BOA because the team’s previous research (Acharya et al. 2021; Acharya et al.2022 in draft) from INRC Project no. 2019-1 showed seedling disease of corn was more severe in the presence of MBOA and BOA. Methodology was developed to run project samples.
Other activities included three presentations and development of a manuscript, “Effect of cereal rye allelochemicals on Pythium species and corn seedling growth and disease,” which will be completed and submitted when results from the GCMS analysis can be incorporated.