Furthering our understanding of the role of cereal rye allelochemicals in the cereal rye-corn production system

Issue

The results obtained from the INRC funded grant (Project no. 2019-1) entitled “Mitigating reduced yields of corn following a cereal rye (Secale cereale) cover crop: what role does allelopathy play?” improved our knowledge on (i) the effect of rye allelochemicals on corn growth and development, and (ii) the interaction between the Pythium spp. commonly associated with corn seedling disease and rye allelochemicals on corn seedling growth and disease development.

Several further questions and queries have arisen from this research that we propose to follow up on. Since our past research evaluated only one allelochemical produced by rye (6-Methoxy-2-benzoxazolinone; MBOA), and was done using synthetic MBOA, we propose to evaluate the effect of the myriad of allelochemicals produced naturally from young and old rye plants on corn seedling growth and disease to build on our previous research and further our understanding.

Objective

The central hypothesis of our proposed project is when corn is planted into rye residue that is terminated within a week of planting corn, corn growth is stunted and seedling roots are more rotted because rye allelochemicals negatively affect corn seedling growth and enhance seedling disease caused by Pythium spp.

Objectives:

1. Assess the effect of leachates produced by cereal rye on corn seedling growth.
2. Assess the effect of leachates produced by cereal rye on the growth of Pythium species belonging to different clades.
3. Study the interaction between the Pythium spp. belonging to different clades and cereal rye leachates on corn seedling growth and disease development.

Approach

For objectives 1-3, a plate assay will be used (Acharya et al. submitted).

Production of leachates: Two varieties of cereal rye, Bonel (high concentration of allelochemicals produced) and Elbon (5-fold less concentration of allelochemicals produced) (Burgos and Talbert 1999) will be planted in cups and left to grow for 14 or 28 days in a growth room at 20 °C with 16 h of light and 10 °C with 8 h of darkness. After 14 and 28 days, rye will be terminated. Leachates will be collected from the cups of terminated rye using methods developed in Greg Tylka’s lab at Iowa State University (Harbach 2019). A sample of each leachate will be analyzed by HPLC at the ISU Chemical Instrumentation Facility (https://www.cif.iastate.edu/mass-spec/prep-lc) to quantify the concentration of the various allelochemicals present. Using two varieties of rye and two growth stages will allow us to produce a gradient of allelochemical concentration.

Plate assay: Briefly, the growth of corn (Obj. 1), four Pythium species belonging to Clades B and F (Obj. 2), and corn seedlings plus each Pythium species (Obj.3) will be evaluated on media amended with the allelochemical leachates from cereal rye. The plates will be placed in the dark at 12°C (55F), and 22°C (72F). The lowest temperature represents soil temperatures in Iowa at corn planting. Five corn seed will be spaced evenly apart around the perimeter of a Petri dish of amended media. A 5mm disc of Pythium sp. will be placed in the center of a Petri dish of amended media. Each treatment (Pythium sp. alone, corn alone, Pythium sp. + corn) will be replicated six times and each experiment repeated twice.

Each treatment will be replicated six times and each experiment will be repeated twice.

Corn seedling growth parameters (emergence, radicle length, shoot length, shoot dry weight) and percent of seedling root rot of each seedling will be recorded at corn growth stage V2-V3 following methods described in Acharya et. al. (2020). ANOVA will be performed using Proc GLIMMIX in SAS for all variables measured. If treatment effects will be detected, Fisher’s protected least significant difference (LSD) will be used to separate treatment means at P = 0.05.